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Food, Flowers and Perfume
Through mantra, mudra, nyasa, yantra, and all the other numerous elements of Tantric ritual, the initiates carve a sacred niche for themselves out of ordinary reality - Tantra: The Path of Ecstasy, Georg Feuerstein The intricate forms of worship (puja) described on some of these pages often require the use of ritual accessories (upacharas), such as specific types of food, flowers and fragrances. For the way in which these are used in a daily rite, refer to the translation of Subhagodaya found on this site.
Some tantrik texts prescribe a whole range of different substances for occasional or optional rites which may include different scents, flowers, edible food and liquids to perform the pujas.
There are plenty of traps for the unwary. While these accessories can relate to external worship (bahiryaga), they may also be used as symbols for internal worship (antaryaga), and so can take a range of forms from the very simple to the very complex. For example, in the Kaulajnananirnaya, the flowers to be offered represent qualities to be cultivated.
"The first flower is non-harmfulness, the second [is] sense restraint, the third generosity, the fourth [is] right disposition, the fifth compassion and the sixth freedom from cruelty. The seventh flower is meditation and the eighth flower is knowledge. Knowing these rules relating to flowers, one should worship this mental lingam." (op.cit III, 25-26).
These flowers are related in this text to different chakras (wheels) or padmas (lotuses) in the human body.
The simplest accessories relate to the five elements of tantrika, and so, by extension, to the five senses. See, for example, the Shani puja, where scent is linked with the bija Lam and earth, flowers to aether with the bija Ham, incense with air and the bija mantra Yam, flame with fire and the bija mantra Ram, and water to liquid and the bija letter Vam.
This inner practice demonstrates two very important yogic elements of puja. The first is that the deva or devi, through meditation (dhyana), whether gross, subtle or supreme, is considered to be one with the worshipper. The second is that by offering the sense impressions to that devata, it encourages the perception that the person performing the rite is not wholly identified with her or his impressions.
These, along with the instruments of the impressions, the five senses, pull the inner self this way and that, and, as can be seen from the prayoga or practical application of the Bhavana Upanishad, are considered to be shaktis or attendants of Paramashakti, the supreme goddess herself. In this connection, it is also worth looking at this page, which describes the physical and metaphysical apparatus of a human being, as an embodiment of Shiva Shakti.
This underlies what some tantriks have described as the ulta sadhana, a reversal of the ordinary condition of the human being, who tends to wholly identify with one, two or several of the lesser shaktis, and so forgets her or his true nature.
The practice of daily puja and the use of these ritual accessories is, then, recommended in the initial stages of sadhana as a way of reminding an individual of the unity of knower, knowledge and known - or worshipper, worship and worshipped.
Food and Liquids Bearing these important considerations above in mind, we can turn to the elements used in puja. In the English introduction to the Gandharva Tantra on this site, chapters 16 and 17 allude to the ritual accessories (upacharas) which may be employed when worshipping Shri Shri Tripurasundari (Lalita). Food offered to a devata becomes holy (prasad) but that doesn't mean it's put to waste and it can be eaten afterwards by a sadhaka.
It doesn't have to be vegetarian food. While most Hindus in modern-day India are vegetarians, some scholars consider this to be a consequence of the rise of the Vaishnavi movements. Bali (animal sacrifice) is viewed as an essential in many of the tantrik texts themselves, although even this has an inner meaning. The bipeds and quadrupeds to be sacrificed must be male.
"O dark one, wondrous and excelling in every way, becomes the accomplishment of those worshippers who living in this world freely make offering to Thee in worship of the greatly satisfying flesh, together with hair and bones, of cats, camels, sheep, buffaloes, goats and men." Karpuradistotra v.19, Woodroffe's translation
According to the Kaula commentary on this verse, the animals represent six enemies to sadhana, the goat standing for lust, the buffalo anger, the cat greed, the sheep delusion, the camel envy, and man pride and arrogance. This is all very well, but animal sacrifice is still practised today in nominally Shakta areas.
As recently as 1980, a goat was sacrificed to Kali at her temple at Amber fort in Rajasthan, a practice banned by the government, which does not, however, seem to have taken similar steps against Pizza Hut or MacDonalds in India. (Sacrifices of quadrupeds to the multinationals seems to be OK, just as long as no religious element is involved.)
In practice, it seems that many tantriks are happy to use substitutes for real animals, such as cucumbers, brinjals and the like.
The Gandharva Tantra classifies food into four types, including liquids, and because it is to be offered to the goddess Tripurasundari, must be of the best quality and also served suitably, depending on the abilities of the practitioner. Fruit, sweetmeats, rice and other dishes are offered to the Devi while reciting a mantra.
The liquids used for worship range from pure water right up to wine, with the Gandharva even including recipes for the alcoholic substance. While wine is an integral part of the panchatattvas, in the chapters on the secret sadhana found in the Devirahasya, mantras and rituals must be performed in order to remove curses on the liquid uttered by Brahma and Shukra. Wine, in this latter tantra, has its own divinity, Suradevi, and she has her own dhyanas and mantras.
Wine, being the Devi herself in liquid form, can be understood as a symbol for the bliss arising from the realisation from work on oneself. A number of tantras caution against taking the text to advocate wholesale drunkenness (Kularnavatantra). When a pot of wine is seen, one should bow to it, as if to the Goddess herself (Kulachudamani, Brihadnilatantra). The Kularnava pours scorn on those who take tantrik texts literally, pointing out that if merely drinking wine, copulating and eating flesh and fish produced liberation, then many humans would already have achieved the state. This last passage refers to the rite known as panchatattva, the five things - often referred to as the panchamakara. These are the five elements starting with the letter "m" are madya (wine), mamsha (meat), matsya (fish), mudra (grain) and maithuna (sexual intercourse). There is a great deal of discussion in various tantrik schools about the significance of these elements in Virasadhana, but most agree that it is a special method prescribed only for heroes and heroines (vira), and unsuitable for the common herd (pashu).
Aside from being a swipe at Brahmin orthodoxy, which views some of these elements with deep abhorrence, some important tantras, including the Kularnava, give them a metaphysical meaning. Some tantras vary the substances depending on the varna (Brahmin, Kshatriya etc). The Yoginitantra and other important texts also give the makaras a symbolic meaning.
There is no agreed view on these matters. It is hard to take some verses of the Yonitantra or the Brihadnilatantra metaphorically, while the commentary on the Karpuradistotra, referred to above, specifically advocates the consumption of semen after ritual sexual intercourse. The Chandamaharoshana Tantra (see Bibliography), a text of the Vajrayana which is, however, spoken of as a source in the Kaulavalinirnaya, is as explicit as you can get about these matters. Woodroffe says in his introduction: "The text goes on to say that there are people who regard semen and menstrual fluid with disgust (Vicharayet), but they forget that the body by .which they hope to attain Liberation is composed of these two forms of matter, that the narrow, bone and. tendons have come from the father and the skin, flesh and blood from the mother. It further says that there is no reason for man's disgust for excreta or urine, for these are nothing but food or drink which has undergone some change and contains living creatures and the Brahman substance is not absent therefrom. The purity that man ought to cultivate is that of the mind. All things are pure. It is one's mentality (Vasana) which is evil."
There is a variety of other, somewhat less contentious, liquids often referred to in tantrik texts which require some explanation. The panchagavya are the five products of the cow, including dung and urine. These are often consumed, although some texts also ascribe an inner meaning to these substances, related to Shakti.
The Gandharva describes padya (water for washing the feet), achamana (water for sipping), madhuparka (a sweet mixture of water, ghee, honey and other substances), and arghya (an offering to the Sun, poured over the head).
Flowers, Scents, Perfumes and Incenses There is a huge variety described in the literature, which almost merits a book of its own. Incense (dhupa) is frequently employed in the daily puja, and this may and often is accompanied with various unguents (anjana), sweet smelling powders, oils (such as sandal oil) and other substances.
Most of the tantrik texts available give pride of place to five fragrances, which, according to lists in Rai's Encyclopedia of Yoga, are for Shakti or Devi agaru (aquilaria agallocha), karpura (camphor), kumkuma (crocus sativus), rochana (convolvulus turpentium) and jatamamshi (asparagus racemosa).
Sandalwood (chandana) and other pleasant fragrances often find themselves on the lists.
Flowers for the worship of Shakti, should normally be red, although this may vary depending on the type of rite, with other colours, including white and orange, often being employed.
As by now we've come to expect, the vamachara tantras interpret flowers and scents in a way all of their own. Flowers (pushpa) has a similar meaning in Sanskrit to English, and are taken by some texts - for example the Matrikabheda Tantra, the Mahakalasamhita and other texts, to refer to menstrual blood. These are classified in different ways, depending on age and the qualifications of a Shakti.
Some of these may have the same name as other fragrances and scents - a trap for the unwary, who in this, as in all other matters, is to be guided by the guru. The Matrikabheda describes the use of menstrual fluids in a somewhat mysterious alchemical process - similar passages are to be found in the alchemical chapter in the Brihadnilatantra.
Biology (A-Z)
American Concise Encyclopedia
Abiotic factors Physical and chemical conditions that affect the ability of a given species to live and reproduce in a particular place. Included in the abiotic factors are temperature, light, water, oxygen, pH (acid-base balance) of soil, type of substrate, and the availability of minerals. Certain kinds of plants and animals will flourish in a natural community if the conditions are present that permit their survival. Species interact to influence the survival of one another. One important principle of ecology is that no living organism is independent of other organisms or of the physical environment, if they share the same community.
Abscisic acid A growth-inhibiting plant hormone produced in the bud that helps to prepare the plant for winter by directing the leaf primoridia to form scales and by inhibiting cell division in the vascular cambium.
Abscission layer A layer along which a leaf or fruit naturally separates from the stem.
Absorption The passage of dissolved materials through the cell membrane, into and out of the cell.
Acetylcholine A neurotransmitter secreted by motor neurons. When an impulse arrives at the knobs in the axon branches of a motor neuron, a neurotransmitter is released from the synaptic vesicles. Neurotransmitters are chemical substances that diffuse across the synaptic gap and initiate a second impulse when chemoreceptors on the dendrites are stimulated. Cholinergic cells secrete the neurotransmitter, acetylcholine. Adrenergic cells secrete the neurotransmitter, epinephrine.
Acid rain This is rainfall that can be as acid as vinegar. It is formed when gases of nitrogen oxide and sulfur dioxide are given off into the atmosphere as by-products of fuel combustion by automobiles, homes, factories, and power plants. As the fumes are carried into the air by wind currents, they combine with water vapor molecules and are transformed into microscopic drops of nitric acid and sulfuric acid. When it rains or snows, the precipitation returns the acids to earth, sometimes thousands of miles from their origin. Lakes and streams have become so acidified that the populations of trout, salmon, and other fish are being destroyed. There is also concern about the possible effects of acid rain on soil minerals and nitrogen-fixing bacteria.
Acquired characteristics Variations that cannot be passed from parent to offspring. These variations are not in the individual's gene pool. Lamarck (1809) advanced the hypothesis that acquired variations are transmitted to the offspring. According to him, structures that are in use are better developed and preserved, whereas unused organs eventually disappear. Characteristics thus acquired through use could be inherited, he thought, by the next generation. Facts do not seem to support his conclusions.
Acromegaly A condition of overgrowth of the bones in the hands, feet, and jaw brought on by an oversecretion of somatotropin by the pituitary gland.
Acrosome The forward tip of an animal sperm that contains the enzymes that help the sperm penetrate the egg. See Sperm.
ACTH (adrenocolticotropic hormone) Stimulates the cortex of the adrenal gland to produce a number of hormones, including cortisone. In severe cases of rheumatoid arthritis, it has brought about dramatic relief from disability and pain.
Actin One of the major proteins of muscle. The other muscle protein is myosin. Actin makes up the Z band of a sarcomere.
Action potential The graph of an action potential demonstrates the sequence of events involved in the transmission of a nerve impulse. A threshold value (Ecrit.) must be attained before depolarization occurs. Once the threshold value is reached, an impulse is generated throughout the nerve fiber. A nerve cell will transmit the impulse either totally or not at all. There are no graded responses. This maximal firing condition is referred to as an "all or none response."
Activation energy The smallest amount of energy that must be available from an outside source that enables a chemical reaction to start.
Active site The specific place on the surface of an enzyme where a substrate attaches by weak chemical bonds and where catalysis occurs.
Active transport The movement of a substance across the cell membrane against a concentration gradient, that is, from a region of low concentration to a region of high concentration. Active transport involves the expenditure of energy.
Adaptation A trait that aids the survival of an individual or a species in a given environment. An adaptation may be a structural characteristic such as the hump of a camel, a behavioral characteristic such as the mating call of a bull frog, or a physiological characteristic controlling some inner workings of tissue cells. Adaptations permit the survival of species in environments that sometimes seem forbidding. For example, some bacteria are able to live in hot springs that have temperatures up to 80 degrees C (175 degrees F). They have adaptations that permit the carrying out of metabolic functions at extremely high temperatures.
Adaptive radiation The evolutionary division of a single species into several species adapted to divergent forms of life. For example: Darwin's finches.
Adenine A nitrogenous base contained in DNA.
ADH (antidiuretic hormone) Also called vasopressin. A hormone secreted by the hypothalamus that prevents the excretion of urine by stimulating the kidney nephrons to reabsorb water.
Adrenals Compound glands located at the top of the kidneys. They have an outer zone known as cortex and an inner one known as medulla. The cortex secretes a complex of substances appearing to be closely related chemically. Their combined action controls sodium, potassium, and chloride metabolism, which affects water balance, causes the change of glycogen to glucose, and influences sex. Deficiency results in a syndrome known as Addison's disease. The patient suffering from it experiences a general decline in muscular strength and sexual activity, a lowering of blood pressure, disturbance of digestion, and a bronzing of the skin. The best-known cortical secretion is cortisone, which has been used in treating arthritis and allergies. The medulla secretes a hormone called epinephrine (adrenaline), which is produced in accelerated quantities when one is stimulated by anger or fear. Apparently it is the only endocrine gland directly responding to nervous stimuli. The influence of epinephrine on the conversion of glycogen to glucose, stimulation of heart muscles, enrichment of blood supply to muscles, and acceleration of blood coagulation are without doubt useful to provide more and quick energy or to stop bleeding in times of stress or injury.
Afferent or sensory neurons Nerve cells that transport impulses from sense receptors to the central nervous system.
AIDS AIDS is a baffling disease that has recently attracted considerable attention. The name stands for "acquired immune deficiency syndrome." It refers to a severe breakdown in the body's immune system. A person with AIDS is vulnerable to a variety of infections and tumors that would normally be attacked by the body's white blood cells. As a result, the person becomes weak and dies. The cause of AIDS is a virus. It was identified in 1984 by Dr. Luc Montagnier of the Pasteur Institute in Paris, who called it LAV- I, and also named by Dr. Robert C. Gallo of the National Cancer Institute, HTLV-III. It is now known as HIV, or human immunodeficiency virus. It is believed that the AIDS virus kills a specialized type of white blood cell, called the helper T4 cell, which normally protects the body from infection by destroying foreign substances that enter it. The disease is believed to be passed through blood and semen, but not passed by casual contact, such as sneezing or using the same utensils. In the United States, certain groups of people have the greatest risk of getting the disease: male homosexuals, intravenous drug users who share contaminated needles, and babies born to infected mothers. Before 1987, recipients of contaminated blood transfusions contracted AIDS. In Central Africa where AIDS is prevalent the disease is also spread by heterosexual contact. Heterosexual transmission is also becoming more common in the United States. Considerable research is being conducted to develop a defense against the disease. In 1986, a drug, azidothymidine (AZT), was found to be effective against a form of pneumonia common among AIDS patients. It appears to interfere with reproduction of the virus inside the body cells. In the near future, it is hoped that research will produce a vaccine against the virus. See also Health and Medicine.
Air sac See Alveolus (air sac).
Albinism An inherited trait requiring two recessive genes resulting in individuals without pigment.
Algae Simple photosynthetic organisms. Algae may be composed of a single cell, a filament of cells, or a flat plate of cells. Cell walls of algae are made of cellulose. Algae have some characteristics of animal cells. With the exception of the red algae, most algal cells have centrioles. During cell division, most algal cells form a cell furrow like those in animal cells.
Alimentary canal See Digestive system.
Allantois An embryonic membranous sac that stores the nitrogenous wastes of reptiles and birds up to the time of hatching. In mammals, it forms part of the placenta.
Alleles Two or more genes that have the same positions on homologous chromosomes. Alleles are separated from each other during meiosis and come together again at fertilization when homologous alleles are paired, one from the sperm cell and one from the egg cell. Two or more alleles determine a trait.
Allergy The sensitivity of some people to substances that are quite harmless to most other people. The cells of these sensitive people produce antibodies to ward off whatever substance affects them. The antibodies become attached to the tissue cells, rendering the person sensitized. Whenever that particular substance enters the body again, it reacts with the attached antibodies and damages the cells. These damaged cells prompt certain symptoms such as itching, sneezing, tearing eyes, red welts, large hives, fever, and a general feeling of not being well.
Allopatric speciation Speciation brought about when an ancestral population becomes separated by one or more geographical barriers that prevent dispersal. An example is Death Valley where each isolated spring has its own water temperature and salinity and each is a habitat for a different species of pupfish.
Alternation of generations The sea lettuce Ulva is a green algae that lives in saltwater. The life cycle of Ulva is described as alternation of generations because one generation of Ulva is produced sexually by gametes while the next generation is produced asexually by zoospores. The gametophyte generation is a haploid thallus from which small, flagellated gametes are released into the water. They pair off and fuse. Each fused pair of gametes forms a zygote that, after a short time, becomes a diploid thallus of a new generation of Ulva. The diploid thallus is the sporophyte generation. It produces haploid zoospores that develop and grow into a haploid thallus, which is now the gametophyte. Many other simple organisms also have an alternation of gametophyte and sporophyte generations.
Alveolus (air sac) A minute air sac in the lungs through which oxygen enters the bloodstream and through which carbon dioxide and water are excreted from the bloodstream.
Alzheimer's disease Progressive mental deterioration more often in older people. Recent research has revealed that nerve cells in parts of the brain are damaged by an accumulation of amyloid proteins.
Amino acids All proteins are built from small molecular units known as amino acids. The amino acid molecules link together in a particular way through peptide bonds. A dipeptide consists of two amino acids. A polypeptide contains many amino acid molecules. A protein is composed of one or more polypeptide chains.
Amniocentesis The procedure of amniocentesis in which a small amount of amniotic fluid is removed from a pregnant woman and is used to study cells of the embryo. In this way certain chromosomal defects can be determined before birth.
Amnion See Embryonic membranes.
Amniotic fluid The fluid that surrounds the developing embryo in mammals, birds, and reptiles.
Amoeba The members of the phylum Sarcodina are described as being amoeboid. Amoeba proteus is the species most often studied. Species included in the Sarcodina move by means of pseudopods, flowing extensions of the flexible and amorphous body. The pseudopods also serve in food-catching. Most of the sarcodines live in fresh water. A contractile vacuole, an organelle designed to expel excess water from the protist cell body, plays an important role in maintaining water balance. Food is temporarily stored in a food vacuole where it is digested by the action of enzymes.
Amphibian An amphibian must spend part of its life cycle in the water where its eggs are laid and fertilized. The eggs develop into a larval stage, or tadpole, that has fish-like characteristics. In tadpoles breathing is by means of gills, blood is pumped by a two-chambered heart, and swimming is by means of tail and body movements made possible by muscles in the body wall. Most amphibians undergo metamorphosis into a lung-breathing adult with a 3-chambered heart.
Anaerobic Referring to a type of cellular respiration that occurs without oxygen such as fermentation. Referring also to certain species of bacteria, such as the tetanus bacilli, that live in an atmosphere devoid of oxygen.
Anaphase A stage in mitosis in which the chromosomes are pulled apart. See Mitosis.
Angiosperms Flowering plants that form seeds inside ovaries. Examples are apple, rose, and dandelion.
Animal kingdom All animals belong to the kingdom Animalia, a grouping of 29 phyla. Twenty-eight of these phyla include animals called invertebrates because they do not have a vertebral column, or true backbone, the 29th phylum includes the vertebrates, animals with a vertebral column.
Annelid The annelids are segmented worms that live in soil, fresh water, or the sea. Most of the annelids are free-living, although some of the marine forms burrow in tubes and some species (class Myzostoma) are parasites on echinoderms. The body of an annelid is divided into a series of similar segments and is said to be metamerically segmented. Most annelids have a closed circulatory system where the blood is contained in vessels. Enlarged muscular blood vessels function as hearts and pump the blood through the system of vessels. Annelids may be dioecious (have separate sexes) or hermaphroditic. Most annelid species go through a ciliated larval stage known as the trochophore larva. This is a larva of evolutionary importance because the same type appears in several phyla.
Annual A plant in which the life cycle is completed in a single year or growing season, such as corn, tomato, and beans.
Anther Pollen producing organ in the flower.
Antibiotic An organic compound that is made and secreted by a living organism (commonly a mold) and is able to prevent the growth and reproduction of another species. Example: Penicillin is synthesized and secreted by the mold Penicillium notatum.
Antibodies The body produces substances known as antibodies to fight disease-producing agents. Antibody production is a relatively slow process. First of all, the body cells must recognize the invading agent as "foreign" -- an antigen -- and then produce an antibody that is exactly right to immobilize the protein invader. Finally, the blood cells must go into full scale production of this specific antibody. An antibody is specific against "a particle" type of germ. For example: diphtheria antibodies will not be effective against scarlet fever antigen.
Anticoagulant A substance that prevents blood from clotting. Heparin is an anticoagulant.
Anticodon A "triplet" of nucleotides in transfer RNA that is able to pair with a complementary triplet (a codon) in messenger RNA, thus arranging transfer RNA to the proper site on the messenger RNA.
Antigen A foreign protein that stimulates the formation of antibodies by the immune system.
Antitoxin An antibody that works against a specific toxin.
Anus The body opening at the posterior end of the alimentary canal.
Aorta A large artery that carries blood away from the heart. See Heart.
Apical dominance A process in which the terminal bud (top of the stem) in plants inhibits the growth of buds at the sides of the stem.
Appendix A small protruding pouch without function positioned where the small intestine joins the large intestine. See Digestive system.
Arachnids The class to which spiders belong. The body of the spider is divided into the cephalothorax and the abdomen. The cephalothorax has six pairs of jointed appendages. Spinnerets at the end of the abdomen are projections through which the spider spins webs. Most spiders breathe by book lungs. Other members of the class Arachnida are mites, ticks, scorpions, horseshoe crabs, and harvestmen.
Archegonium The multicellular, water-retaining structure, in which a single egg is produced and fertilized in the liverworts, mosses, and hornworts.
Archenteron The cavity appearing in the early embryo during the gastrula stage that ultimately becomes the gut cavity.
Arteriole A small artery.
Artery A blood vessel that transports blood from the heart to the organs and tissues of the body.
Arthropods The arthropod group is by far the largest group of animals with respect to the number of species it contains. They share the common characteristics of having segmented bodies, jointed appendages, and exoskeletons.
Asexual reproduction Involves only one parent. The parent may divide and become two new cells, thus obliterating the parent generation. Or the new individual may arise from a part of the parent cell; in such a case, the parent remains. Types of asexual reproduction are binary fission, sporulation budding, regeneration, and parthenogenesis.
Assimilation Involves the changing of certain nutrients into the protoplasm of cells.
Atoms Elements are made of invisible building blocks called atoms. Each atom has a central nucleus surrounded by a definite number of moving negatively charged electrons.
ATP (Adenosine triphosphate) The compound that stores energy produced during cellular respiration and releases this energy when needed for the cell's work. Energy produced during cellular respiration is passed on to adenosine diphosphate (ADP), which then becomes upgraded to ATP.
Atrium The chamber of the heart (also known as the auricle) that receives blood and passes it to the ventricle for pumping.
Autonomic nervous system See Nervous system, autonomic.
Autosome A chromosome that does not determine sex. Human cells have 22 pairs of autosomes.
Autotrophs Organisms that are able to change inorganic materials into organic compounds. Among these are the photosynthetic bacteria and the green plants that use light energy to produce food. The chemosynthetic bacteria are capable of oxidizing the inorganic compounds of ammonia, nitrites, sulfur, or hydrogen gas into high-energy, organic compounds without the need of light energy.
Auxins Plant hormones called auxins are produced by actively growing plant tissues like the growing tips of roots and branches, developing leaves, or flowers and fruits. They promote cell enlargement, which is one phase of growth (the other is cell division).
Axon Extension of the neuron (nerve cell) that can carry impulses; is often the longest and least branched process of the cyton (cell body) and usually carries impulses away from the cell body of the neuron.
B cell A white blood cell known as a lymphocyte produced in the bone marrow that works with T cell lymphocytes to destroy germs.
Back cross (test cross) Plant and animal breeders mate an individual with a particular dominant trait to an individual that is recessive to determine if the dominant trait is pure or hybrid. As a result of this mating, if organisms appear that have the recessive trait, then the breeder knows that the parent individual is hybrid (heterozygous) for the dominant trait.
Bacteria Bacteria are the smallest living organisms. They range in length from 0.2-7 micrometers; in diameter from 0.2-2 micrometers. As you recall, the unit used to measure bacteria is the micrometer and is equivalent to 1/1000 of a millimeter. The smallest cells known are the mycoplasmas, which have only one-half the DNA of other bacterial cells. The mycoplasmas are bacteria that live only as parasites on or in the bodies of plants and animals. Despite their small size bacteria are true cells: they provide their own genetic material (DNA and RNA) and the necessary cytoplasm for their own reproduction; they have multienzyme systems to control biochemical activities necessary for the life of the cell; and they build their own ATP molecules and use the stored energy to synthesize other organic compounds. Bacterial shapes include spheres (cocci), rods (bacilli), and spirals (spirilla). See also Eubacteria -- true bacteria.
Bacteriophage A virus that infects a bacterial cell.
Biennial A plant for which the life cycle is two years. Vegetative growth occurs during the first year; flowering, the second. Beets and carrots are examples.
Bilateral symmetry Two sided, as demonstrated by animals that have an anterior (head end) and a posterior (tail end), a right and left side that are similar. For example: a human being shows bilateral symmetry, as does a horse. If sliced down the middle, each has two identical halves.
Binary fission A form of asexual reproduction in which a parent organism divides into two identical daughter cells. The nucleus goes through mitosis. The cytoplasm divides equally.
Binomial nomenclature The scientific naming of species by a double name. The first name in the binomial is the genus name. This system was developed by Carolus Linnaeus (1707-1788) and has become a worldwide standard for classifying and naming organisms.
The Genus Quercus Scientific Name Common Name Quercus alba white oak Quercus coccinea scarlet oak Quercus montana chestnut oak Quercus rubra red oak Quercus suber cork oak Quercus virginiana live oak
Biogenesis The doctrine that living things come only from other living things of like kind.
Biogeochemical cycles Certain compounds cycle through the abiotic portion and the biotic communities of ecosystems. These compounds contain elements that are necessary to the biochemical processes that are carried out in living cells. Among these elements are carbon, hydrogen, oxygen, and nitrogen. In elemental form, they are useless to cells and must be combined in chemical compounds. Let us trace the pathways of some of the vital compounds from the earth to living organisms to the atmosphere and back to earth. This cycle of events is best described by the term biogeochemical cycles. See figure.
Biology The study of living things; an extensive science including botany, zoology, bacteriology, genetics, physiology, anatomy, and many others.
Biome A climax community in a broad geographical area having one type of climate. Examples of biomes are the Taiga, coniferous forests of Canada; the Desert, regions where the annual rainfall is less than 6.5 centimeters; the Grasslands, annual rainfall is low and irregular; the Tropical Rain Forest, characterized by high temperatures and constant rainfall; and the Marine biome, the sea.
Biomes, world A climax community in a broad geographical area having one type of climate is known as a biome. The earth is divided into several biomes.
The Tundra. Vast stretches of treeless plains surrounding the Arctic Ocean where cold is the limiting factor. Plant life consists of lichens, mosses, grasses, and sedges. Animal life includes the musk ox, caribou, polar bears, wolves, foxes, and some marine mammals.
The Taiga. The coniferous forests of Canada and Russia where spruce and fir trees predominate. The kinds of mammals that live in this region are the black bear, the wolf, lynx, and squirrel.
The Deciduous Forest. These are forests of temperate regions, where broad-leaved trees that lose their leaves in the winter predominate. The types of animals that live in these forests are deer, fox, squirrel, skunk, woodchuck, and raccoon.
The Desert. Deserts form in regions where the annual rainfall is less than 6.5 centimeters and where evaporation of water is high. Creosote, sagebrush, and cacti are plants adapted for the desert. The animals include lizards, insects, kangaroo rats, and arachnids.
The Grasslands. These regions have low annual rainfall. Grasslands are located in regions that are sheltered from moisture-laden rainfall. The animals that predominate in temperate grasslands, called steppes or prairies, are bobcats, badgers, hawks, kit foxes, owls, and coyotes. Typical animals of tropical grasslands or savannas are zebras, giraffes, baboons, and gazelles.
The Tropical Rain Forest. The tropical rain forest is characterized by high temperatures and constant rainfall. This type of biome is found in Central and South America, in Southeast Asia, and in West Africa. The trees are tall and the vegetation is so thick that the forest floor is shaded from light. The animals of the rain forest include monkeys, lizards, snakes, and birds.
The Sea. Ocean waters cover almost three fourths of the earth's surface and support the greatest abundance and diversity of organisms in the world. Averaging 3.5-4.5 kilometers in depth, a marine biome constitutes the thickest layer of living things in the biosphere. The dominating physical factors determine the type of living organisms that compose its communities.
Biometrics The science that combines mathematics and statistics needed to deal with the facts and figures of biology. Biologists handle enormous numbers that must be organized and simplified so that they become useful in the analysis of data.
Biotic environment The part of the environment that is living and has some effect on other living organisms.
Bipedalism The ability to walk on two legs instead of four. Bipedalism has freed the forearms for doing work.
Birds Birds are terrestrial vertebrates with feathers. Feathers are the distinctive feature of birds: all birds have them and no other animals are so covered. The forelimb is modified into wings for flight, leaving the hindlimbs for walking (bipedal locomotion). Birds are built for flight; special adaptations in body structure effect lightness in weight, efficiency, and strength. Not only are the feathers light in weight and easily moved and lifted by wind, but they also create warmth next to the body. Body heat warms the air that is in contact with the bird's body. Warm air becomes lighter and rises. Other adaptations for flight are the compact, but hollow, bones, numerous air sacs occupying all available body spaces, reduced rectum, loss of teeth, and feathers replacing a bony tail.
Bivalves Animals, such as clams, that have the body encased within two hinged shells. Lining the inner surfaces of the shells is a membranous mantle. The cavity inside of the shells is the mantle cavity.
Blastula An early stage in animal embryology; a hollow ball of cells surrounding a central cavity. See Cleavage.
Blood A liquid tissue consisting of a liquid medium called plasma and three kinds of cells: red blood cells (erythrocytes), white blood cells (leucocytes), and platelets. There are about 25 trillion red blood cells in the human body. For each 600 red blood cells there is one white blood cell. Blood cells number in the billions. The red blood cells carry oxygen. The white blood cells function in immune reactions.
Blood clotting Platelets are the smallest blood particles. When a capillary is cut, the platelets collect at the site of the injury. There they break into smaller fragments and initiate the complicated chemical process of blood clotting in which more than 15 factors, including thromboplastin, calcium (Ca27), and fibrinogen, are involved in the formation of a clot containing blood cells in a fibrin meshwork.
Blood types The main types of blood are A, B, AB, and O. Transfusions of blood are possible only when the blood types are compatible. If the blood types are not compatible proteins in the plasma will recognize foreign antigens on red blood cells and respond by causing the cells to agglutinate, or clump, a condition that causes blockage in small blood vessels and often death. The following table summarizes the blood proteins involved in blood types.
Proteins of Blood Types Blood Cell Plasma Type Antigen Antibody A A b B B a AB AB none O none a and b
Note: Type AB -- universal recipient Type O -- universal donor
Bone The living tissue that comprises the skeleton. Bone tissue is made of cells that are surrounded by hardened calcium phosphate.
Bowman's capsule See Nephron.
Brain The brain and the spinal cord compose the central nervous system. In the vertebrate body, the organs of the central nervous system are well protected by being wrapped in connective tissue and enclosed in bone. The brain, covered by the membranous meninges, rests in the skull cavity where it is enclosed by the cranium. The spinal cord, also covered by connective tissue, is circled by the vertebral column. The human brain is divided into many parts, each with special functions. Among the most important parts are the cerebrum, cerebellum, and medulla.
Bronchi (Bronchus) Two tubes made of cartilage rings that extend from the windpipe (trachea) into the lungs (See Lungs).
Bronchioles Small tubes in the lungs that branch off from the bronchi. Each bronchiole ends in an air sac called the alveolus. See Respiratory system.
Bryophytes The bryophytes are the first green land plants. They are primitive, small, and inconspicuous. Although multicellular, the tissue differentiation is quite simple. Bryophyte species have no tissues that are specialized for water-carrying and no cambium specialized for growing new cells. Bryophyte species do not have true stems, leaves, or roots. Simple rootlike structures called rhizoids anchor the plants to the ground and absorb moisture from the soil.
Budding A form of asexual reproduction in which the parent cell body gives rise to a bud. The bud has the same number and kind of chromosomes as the parent cell, but has much less cytoplasm than the parent cell. The bud develops into a new individual. Example: yeast cells reproduce by budding.
Calorie The amount of heat required to raise the temperature of one gram of water by one degree Celsius (1 degree C). (A kilocalorie is the amount of heat needed to raise the temperature of one kilogram of water by 1 degree C.)
Calvin cycle The second major stage of photosynthesis involves reductive carbon dioxide fixation. Because the cyclic reactions that function at this time do not require light as a source of energy, the term dark reaction has been used to designate this phase of photosynthesis. Calvin and his associates determined the path of carbon in the carbon dioxide by the use of 14C. See Photosynthesis.
Cambium See Woody stems.
Capillary The smallest blood vessel.
Carbohydrates Are characteristically composed of carbon, hydrogen, and oxygen in the proportion of CH2O. The hydrogen and oxygen are in the same proportion in carbohydrates as in water.
Carboxyl group See Amino acids.
Carcinogen Any substance or radiation that causes cancer; asbestos, the herbicide dioxin, or radiation from radioactive materials, sunlight, or X rays are examples.
Carnivores Flesh eaters such as snakes, frogs, hawks, and coyotes.
Carrier-facilitated diffusion Transport of a substance across the plasma membrane by carrier molecules but without energy. This process cannot effect the net transport of a substance from a region of low concentration to a region of high concentration. This is a form of passive transport.
Carrying capacity In ecology, the largest number of organisms of a given species that can be maintained indefinitely in a particular part of the environment.
Cartilage A specialized type of dense connective tissue not as hard as bone, in which the cells are contained in a rubbery matrix that is smooth, firm, and flexible: occurs in joints, at the end of bones, and in the ears, nose, and windpipe.
Catalyst A chemical substance that speeds up a reaction without itself being used up in the overall course of the reaction. Enzymes are biological catalysts.
Cell Each cell is a living unit. Whether living independently as a protist or confined in a tissue, a cell performs many metabolic functions to sustain life. Each cell is a biochemical factory using food molecules for energy, repair of tissues, growth, and ultimately, reproduction. On the chemical level, the cell carrries out all of the life functions. Living organisms function the way they do because their cells have the properties of life.
Cell division When a cell reaches a certain size it divides into two new cells, identical to each other and very similar to the original parent cell. The new cells are known as daughter cells. The events marking cell division differ in prokaryotes and eukaryotes. See Mitosis.
Cell membrane The outer boundary of the cell, also called the plasma membrane, about 10 nanometers in width. The cell membrane controls the movement of substances into and out of the cell in a process known in general as transport. Highly selective as to the substances that cross its boundary, the cell membrane is said to be semi-permeable. Using the concept demonstrated by the fluid mosaic model, biologists explain how some molecules are able to penetrate the cell membrane while others cannot. According to this model, the core of the membrane is made up of phospholipids. Large circular proteins are set into the membrane; smaller proteins lie on the surface. The proteins and the phospholipids have special functions and form certain structural pathways that serve to admit or deny passage to specific molecules.
Cellulose A straight chain polymer of glucose molecules secreted by plants and used as structural supporting material.
Cell wall A relatively rigid structure composed of cellulose that encloses the cells of plants. The cell wall gives these cells their shape and limits their expansion in hypotonic media.
Central nervous system See Brain.
Centrioles Paired structures that lie just outside of the nucleus of nearly all animal cells and some cells of lower plants. They are absent in cells of higher plants. Under the light microscope, the centrioles look like two insignificant granules, but the electron microscope demonstrates that they have a very intricate structure.
Cerebellum See Brain.
Chemosynthesis The production of high-energy organic compounds from inorganic raw materials without the aid of light energy by some bacteria that live on ammonia, nitrogen, and sulfur.
Chitin Tough, nitrogen-containing polysaccharide that is present in the exoskeletons of insects and in the cell walls of most species of fungi.
Chlorophyll See Chloroplasts.
Chloroplasts A group of structures that has the general name plastid. Plastids are membrane-bound organelles found only in plant cells. Usually plastids are spherical bodies that float freely in the cytoplasm, holding pigment molecules or starch. Chloroplasts contain the green pigment chlorophyll, a substance that gives plants the green color. Chlorophyll is a special molecule that has the ability to trap light and to convert it to a form of energy that plants can use in carrying out the chemical steps of the food-making process known as photosynthesis. Each chloroplast is surrounded by a double membrane. Inside the chloroplast are numerous flattened membranous sacs called thylakoids (formerly called grana). The thylakoids are the structures that contain the chlorophyll and it is within these sacs that photosynthesis takes place. Stroma is the name given to the dense ground substance that cushions the thylakoids. Animal cells do not have chloroplasts and therefore cannot make their own food. The figure shows the fine structure of a chloroplast.
Chordates Set apart from lower animals by several distinguishing characteristics in addition to having a notochord. First, all chordate embryos have the three primary germ layers from which all specialized tissues and organs develop. Second, chordates are bilaterally symmetrical animals with anterior-posterior differentiation. Third, the body has a true coelom and a digestive tract that begins with a mouth and ends with an anus. Other characteristics that differentiate the chordates from other animals are the presence of pharyngeal gill slits and the dorsal hollow nerve cord.
Chromatography A technique of separating substances, such as proteins in a complex liquid, by varying their rates of absorption on media such as filter paper or in a column of silicia gel.
Chromosomes In the nucleus of the nondividing cell is a tangle of very fine threads that absorb stain quite readily. In the granular stage these threads are known as chromatin. The chromatin threads come together, shorten and thicken forming chromosomes that can be seen quite prominently in the dividing cell.
Chromosome Numbers of Some Common Species Organism Haploid No. Diploid No. mosquito 3 6 fruit fly 4 8 gall midge 20* 8* evening primrose 7 14 onion 8 16 corn 10 20 grasshopper (female) 11 22 grasshopper (male) 10 21** frog 13 26 sunflower 17 34 cat 23 38 human 23 46 plum 24 48 dog 39 78 sugar cane 40 80 goldfish 47 94
* In the fertilized egg of the gall midge, 32 chromosomes become nonfunctional leaving 8 functional chromosomes. ** The male grasshopper has only one sex chromosome.
Cilia See Flagella and cilia.
Circulation Distribution of blood pumped from the heart, through the arteries, arterioles, and capillaries to the body tissues. Blood is carried back to the heart by veins.
Circulatory system The human circulatory system consists of the heart and the system of blood vessels that transport blood throughout the body. See Heart.
Cistron The genetic unit of function, considered equivalent to a gene. Each cistron contains the genetic information for a single polypeptide chain.
Classification The design of the classification system is a simple and practical one that easily lends itself to the addition of new names of organisms as they are discovered. Each group of organisms within the scheme is known as a taxon (plural, taxa). The classification groupings are as follows: kingdom, the largest and most inclusive group, followed by the phylum, class, order, family, genus, and species.
Cleavage The fertilized egg goes through a series of cell divisions in which there is no growth in size of the zygote nor separation of the cells.
Climax community A stable ecological community where one or two large trees predominate.
Clone A population of cells (or whole organisms) that has descended from an original parent cell, which was stimulated to reproduce by asexual means.
Codominance A form of inheritance in which neither of the allelic genes that determine a characteristic is dominant over the other. The result of this inheritance is a blend. When red-flowered primroses are crossed with white-flowered primroses, the offspring have pink flowers.
Codon A "triplet" of three nucleotides in messenger RNA that directs the order of a particular amino acid in a protein molecule.
Coenzyme An organic compound, not a protein, that supports the catalytic activity of an enzyme. Vitamins are coenzymes.
Coenocyte A cell bounded by a single plasma membrane but containing many nuclei.
Cold-blooded animal Poikilotherm. An animal whose body temperature changes with the external environment. Examples: fish, amphibians, reptiles.
Commensalism See Nutritional relationships.
Community All of the plant and animal populations living and interacting in a given environment are known as a community.
Compounds Classified as organic or inorganic. Organic compounds are generally thought of as most compounds of carbon. Inorganic compounds are compounds made of other elements and a few carbon compounds similar to earthlike substances, like calcium carbonate (CaC03). Organic compounds are called organic because of the original belief that they came from living organisms. Today thousands of organic compounds not found in nature are being synthesized in laboratories. Both organic and inorganic compounds are necessary to life.
Conditioned behavior A type of learned response in which a new response becomes associated with an original stimulus.
Conifers (cone bearers) See Gymnosperms.
Conjugation A form of sexual reproduction that is occasionally demonstrated by the ciliates. Two organisms will join together at the oral groove. The micronucleus of each will undergo meiosis, producing several cells. All but two of these in each organism disintegrate. One of these haploid micronuclei remains in each cell, while the other migrates into the other cell, fusing with the stationary gamete. The new nucleus -- which is now diploid and contains a new genetic combination -- goes through cell division producing a new macronucleus and a new micronucleus.
Consumers Primary consumers -- herbivores, or plant-eaters. Herbivores come in all sizes: crickets, leaf cutters, deer, and cattle. The carnivores, or flesh-eaters, such as snakes, frogs, hawks, and coyotes are secondary consumers because they feed on the herbivores. The tertiary consumers are those that feed on the smaller carnivores and herbivores as well. There are also scavengers in the ecosystem. Earthworms and ants feed on particles of dead organic matter that have decayed in the soil. Vultures eat the bodies of dead animals.
Contractile vacuole See Paramecium.
Cotyledons The first leaves of a plant; they are often strikingly different from later leaves. In some plants like the bean, they contain large quantities of stored food that get the embryo off to a good start until it can shift for itself. They are the two halves of the bean seed. Cotyledons usually persist for only a short while after germination.
Crossing over Genes are linked on chromosomes and are inherited in a group on a particular chromosome. However, linkage groups are broken by crossing over, a phenomenon that may occur during meiosis when homologous chromosomes are intertwined during synapsis. It is at this time that chromosomes may exchange homologous parts and thus assort linkage groups.
Crustacea Derived from the Latin crusta meaning crust, the name Crustacea describes the lobsters and their relatives aptly. The body is covered by a tough exoskeleton arranged in the form of arched plates that thin out at the joints to permit maximum movement. The lobster is representative of this class.
Cyclic AMP (cAMP; cyclic adenosine monophosphate) A compound formed from ATP that regulates the effects of numerous hormones in animals (second messenger).
Cyclosis The circulation of cytoplasm within cells. This is especially true in plant cells where there are large vacuoles. Protoplasm flows around the margins and in cytoplasmic strands that sometimes extend through the vacuoles. Protoplasm in adjacent cells may flow in opposite directions, or it may reverse directions in any particular cell. Light and temperature especially influence this action in plant cells, but the exact cause of movement is unknown. Circulation results in a thorough mixing of protoplasm and its contents. Cyclosis of protoplasm in palisade cells of leaves may prevent the overexposure of chloroplasts to light, since they remain in a position of maximum exposure only momentarily.
Cytochromes Iron-containing red proteins; molecules of the electron-transfer machinery in photosynthesis and respiration.
Cytokinesis The division of cytoplasm occurring during the last state (telophase) of mitosis.
Cyton Nerve cell body. See Nerve cell (neuron).
Cytoplasm The ground substance of the cell that supports all of the cell's organelles. See Cell.
Cytosine A nitrogen base that pairs with guanine in DNA and RNA.
Dark reaction The stage of photosynthesis in which carbon dioxide fixation occurs, resulting in the formation of sugar. See Calvin cycle.
Daughter cells See Cell division.
Deciduous forest The forests of the temperate regions are dominated by broad-leaved trees that lose their leaves in the winter. Examples of the kinds of trees that compose these hardwood forests are oak, hickory, chestnut, beech, maples, willows, cottonwood, and sycamore. The types of animals that inhabit these forests are deer, fox, squirrel, skunk, woodchuck, and raccoon.
Decomposers Decomposers form an important part of ecosystems. Bacteria and fungi are organisms that break down dead organic matter and release from it organic compounds and minerals that are returned to the soil. Many of the materials returned to the soil are used by the producers in the process of food-making. Without the work of the decomposers the remains of dead plants and animals would pile up, not only occupying space needed by living organisms, but also keeping trapped within their dead bodies valuable minerals and compounds.
Dehydration synthesis As the two molecules join, a molecule of water is produced during the process in addition to the double sugar. A synthesis of this type is known as dehydration synthesis. Within living cells, carbohydrates, proteins, and fats are formed by dehydration synthesis.
Dendrite See Nerve cell (neuron).
Denitrifying bacteria Soil bacteria that change nitrates back to atmospheric nitrogen. The cycle then repeats.
Deoxyribonucleic acid (DNA) DNA molecules are the particular type of nucleic acid out of which genes are made. Genes are the bearers of hereditary traits from parent to offspring. See also Replication.
Desert Deserts form in regions where the annual rainfall is less than 6.5 centimeters, or where rain occurs unevenly during the year and the rate of evaporation is high. The temperature changes drastically from hot days to cold nights. Plants that survive in the desert have specific adaptations for low moisture and high temperature. Examples of desert plants are creosote, sagebrush, cacti, and cheat grass. Examples of desert animals are lizards, insects, kangaroo rats, and arachnids.
Diaphragm The muscular structure that separates the chest cavity from the abdominal cavity in mammals; in a microscope, the part that regulates light entering the lens system.
Dicotyledon (dicot) A type of angiosperm plant in which the embryo plant is contained between two seed leaves or cotyledons.
Differentiation See Embryo.
Diffusion The movement of molecules from an area of greater concentration to an area of lesser concentration. Diffusion is a type of passive transport.
Digestion Begins in the mouth. Teeth grind the food while three pairs of salivary glands pour salivary juice (saliva) into the mouth. Saliva contains the enzyme salivary amylase (ptyalin), which begins the digestion of starch. The moistened, chewed food is swallowed and moves through the throat into the food tube, or esophagus. The esophagus has no digestive function but moves the food into the stomach by waves of muscle contractions called peristalsis. Chemical digestion is known as hydrolysis. Extracellular digestion takes place outside of cells. Intracellular digestion takes place inside of cells within cell vacuoles.
Digestive system The human digestive system begins with a mouth and ends with an anus, and is often described as a "tube within a tube." Variously called the gut, alimentary canal, or the gastrointestinal tract, the digestive system extends from the lower part of the head region through the entire torso. Essentially, this system carries out five separate jobs that have to do with the processing and distribution of nutrients. First, it governs ingestion or food intake. Second, it transports food to organs for temporary storage. Third, it controls the mechanical breakdown of food and its chemical digestion. A fourth function is the absorption of nutrient molecules. Its final piece of work is the temporary storage and then elimination of waste products.
Dihybrid Mixed genes for two traits. See Heredity, Mendelian.
Dinoflagellates Dinoflagellates are small protists and usually unicellular. Most of these organisms have two unequal flagella, one extending longitudinally from the posterior end of the cell, the other encircling the central part of the cell. Some dinoflagellates extend trichocysts like the paramecium; others have nematocysts, stinging cells common in the coelenterates. Some species -- Noctiluca, for example -- are bioluminescent, giving off light like a firefly.
Diploid number The full complement of chromosomes in somatic (body) cells designated by the symbol 2N; also known as the species number or chromosome number.
Disease A disease is a disorder that prevents the body organs from working as they should. In general, diseases can be classified as being infectious or noninfectious. Infectious diseases are caused by organisms that invade the body and do harm to the cells, tissues, and organs. As a rule, there is disease specificity when a specific disease-producing organism causes a particular disease. Disease-producing organisms are said to be pathogens and are described as being pathogenic. Noninfectious diseases are caused by factors other than pathogenic organisms. Among the factors that are responsible for noninfectious diseases are genetic causes, malnutrition, exposure to radiation, emotional disturbances, organ failure, poisoning, endocrine malfunctioning, and immunological disorders. Whatever the cause, a disease works counter to the well being of the diseased organism.
Dominant trait When organisms with contrasting traits are crossed, the trait that shows up in the F1 generation is called the dominant trait. The trait that is hidden is called the recessive trait.
Double helix See Deoxyribonucleic acid (DNA).
Droplet infection A common method of passing germs along. Disease germs are present in droplets ot water that escape from the nose and mouth when sneezing, coughing, and talking. If these infected droplets are inhaled or taken in by mouth, the germs then enter the body of another person.
Ear and hearing The human ear is made up of three divisions: the outer ear, middle ear, and inner ear. The outer ear catches sound waves and transports them to the eardrum, a membrane that stretches across the outer canal separating it from the middle ear. Sound waves cause the eardrum to vibrate. The middle ear contains three very small bones called the hammer, anvil, and stirrup. These are the smallest bones in the body. These bones accept the vibrations from the eardrum and transmit them to the oval window, one of two small membrane-covered openings between the middle ear and the inner ear. The inner ear, which is entirely encased in bone, has a fluid-filled structure called the cochlea, so named because it resembles a snail in shape. The cochlea has numerous canals that are lined with hair cells. The vibrations from the oval window are transmitted to the hair cells in the cochlea and thence on the auditory nerve, which conducts the vibrations to the brain. In the brain, signals are interpreted into sounds.
Echinoderms Spiny-skinned invertebrates that include the starfish, brittle stars, sand dollars, sea urchins, and sea cucumbers. Although they do not look very much like vertebrate animals, the development of the echinoderm embryo strongly resembles that of the chordates in the early stages. The larval stage is free-swimming and shows bilateral symmetry.
Ecological niche An important concept of ecology is that of the niche. An ecological niche is a feeding pattern exhibited by species that compose a community. A niche is a feeding way-of-life in relationship to other organisms.
Ecology The science that studies the interrelationships between living species and their physical environment. The word "ecology" was coined in 1869 by the German zoologist Ernst Haeckel to emphasize the importance of the environment in which living things function. The environment includes living or biotic factors and nonliving factors referred to as abiotic factors.
Ecosystem The living community and the nonliving environment work together in a cooperative ecological system known as an ecosystem. An ecosystem has no size requirement or set boundaries. A forest, pond, and field are examples of ecosystems. So is an unused city lot, small aquarium, the lawn in front of a residential dwelling, or a crack in a sidewalk. All of these examples reflect areas where interaction is taking place between living organisms and the nonliving environment.
Ectoderm See Embryo.
Effectors The kind of responses that organisms can make is related to their own body equipment. The responding part is the effector. Most animal effectors are either muscles or glands. In considering responses one ordinarily thinks about rapid, visible muscular responses. Glandular responses are much more subtle.
Embryo The stage in human or animal development following cleavage. During embryonic development the tissues and organs are being built. When the embryo takes human or animal form, it is known as a fetus. The process in which tissues are formed is known as differentiation.
Differentiation of the Three Primary Germ Layers Ectoderm Endoderm Mesoderm skin lining of lungs muscles nervous system lining of skeleton digestive system sense organs pancreas heart liver blood vessels respiratory blood system ovaries, testes kidneys
Embryonic membranes The embryo produces several membranes that do not form any part of the new baby but which are necessary to the development and well being of the embryo. One of these membranes is the amnion, a waterfilled sac that completely surrounds and protects the embryo. The water absorbs shocks and prevents friction that might damage the embryo. The implanted embryo is attached to the uterus by means of the umbilical cord, a structure that contains blood vessels that function in carrying nutrients and oxygen to the embryo and transporting wastes away from the embryo. The umbilical cord connects with the placenta, a vascularized organ made up of tissues of the mother and embryo. See Allantois.
Endocrine system Made up of the pituitary gland, thyroid gland, parathyroid glands, the adrenal gland, the isles of Langerhans in the pancreas, the thymus gland, the pineal gland, and the gonads -- testes in the male and ovaries in the female. Certain secretions of the stomach and small intestine are also hormones and thus part of the endocrine system. Through their secretions the endocrine glands regulate growth, rate of metabolism, response to stress, blood pressure, muscle contraction, digestion, immune responses, and the development and functioning of the reproductive system. Hormones exert their influence by becoming involved with the genetic machinery of cells and by affecting the metabolic activities of cells working through the cellular respiration pathways.
Endoderm See Embryo.
Endoplasmic reticulum Spreading throughout the cytoplasm, extending from the cell membrane to the membranes of the nucleus is a network of membranes that form channels, tubes, and flattened sacs; this network is named the endoplasmic reticulum. One function of the endoplasmic reticulum is the movement of materials throughout the cytoplasm and to the plasma membrane. The endoplasmic reticulum has other important functions related to the synthesis of materials and their packaging and distribution to sites needed.
Enzyme-substrate complex An enzyme affects the rate of reaction of the substrate molecule that fits the enzyme's activity site. In order for this to happen, a close physical association must take place between enzyme and substrate. This association is called the enzyme-substrate complex. See Substrate.
Enzymes (organic catalysts) A catalyst is a molecule that controls the rate of a chemical reaction but is itself not used up in the process. Enzymes are proteins that control the rate of chemical reactions that take place in cells, tissues, and organs. Each chemical reaction that occurs in a living system requires the assistance of a specific enzyme (enzyme specificity).
Epinephrine The hormone secreted by the medulla of the adrenal gland; also called adrenaline. It is secreted as a result of stress and produces effects on the circulatory system and on glucose mobilization.
Epithelial tissue See Tissues.
Estrus The period of maximum sexual receptivity in the female mammal. Estrus is also the time of the release of eggs in the female.
Eubacteria -- true bacteria This group, referred to as the true bacteria, represents a large number of species. All of these bacteria have thick and rigid cell walls. Some of the species are nonmotile (nonmoving), while others are motile, using flagella or a sling motion to move from place to place. Species belonging to the eubacteria are identified by their shapes. The rod-shaped bacteria are known as bacilli (bacillus, sing.), the round bacteria as the cocci (coccus, sing.), and the spiral-shaped as spirillae (spirillum, sing.). Some species typically remain attached: diplococci occur in pairs, streptococci in chains, and staphylococci in clusters. See also Bacteria.
Eukaryotes Organisms whose cells contain the genetic material (DNA) enclosed in a nucleus; includes all organisms above the level of bacteria and blue-green algae.
Evolution Concerns the orderly changes that have shaped the earth and that have modified the living species that inhabit the earth. Evolution is a fusion of biological and physical sciences that have provided supporting data that confirm the fact that over periods of time major changes have occurred in the interior of the earth and on its surface, accompanied by modifications in climate. All of the changes in the earth are classified as nonbiological or inorganic evolution. Changes that have taken place in living organisms are known as biological or organic evolution.
Evolution, evidences of Evidence that evolution -- gradual change over a period of time -- has occurred in living things is provided by many sciences and includes facts from the geologic record, the study of fossils, and evidence from cell studies, biochemistry, comparative anatomy, and comparative embryology.
Evolution, theories of Since the eighteenth century several theories have been proposed to explain evolution. Among these are the use and disuse theory of Lamarck and the theory of natural selection formulated by Charles Darwin. Recent advances in genetics cell biology, and functional anatomy and biochemistry have led to the formulation of a modern theory of evolution based on Darwin's concept of natural selection.
Excretion Removes waste products of cellular respiration from the body. The lungs, skin, and kidneys are excretory organs in humans that remove carbon dioxide, water, and urea from the blood and other body tissues. Guttation is the excretion of drops of water from plants during periods of high humidity.
Excretory system In human beings, the lungs, skin, and urinary system work to expel the wastes produced in metabolic activities. The lungs excrete carbon dioxide and water. The skin expels water and salts from the sweat glands and a small amount of oil from the sebaceous glands. The urinary system handles the major work of excretion.
Exocrine glands Glands, such as salivary and sweat glands, from which the secretions are discharged through ducts directly into an organ or onto the surface of the body.
Exoskeleton A hard covering on the outside of the animal body. The exoskeleton of arthropods has the same functions of support as the bony internal skeleton of vertebrates.
Eye The human eyeball measures about 2.5 centimeters in diameter. Most of the eyeball rests in the bony eyesocket of the skull. Only about one sixth of the eye is exposed. External structures associated with the eye are eyelids, lashes, and eyebrows. A transparent protective membrane, the cornea, covers the eye. Six small muscles attach the eye to the eyesocket. Secretions from tear glands help to keep the eye moist. The lens is a transparent body that focuses light on the light-sensitive retina where images are formed.
Fats Organic compounds that supply cells with energy. Fats are usually insoluble in water. A fat results from the combination of one glycerol and three long-chain fatty acids joined through dehydration synthesis. Certain fats are essential to the structure and function of body cells, to the building of cell membranes, and to the synthesis of certain hormones. Fats also aid in the transport of fat-soluble vitamins. Foods rich in fats include butter, bacon, egg yolk, cream, and certain cheeses.
Fermentation See Anaerobic.
Ferns The fern plant used in flower bouquets is the sporophyte generation. The sporophyte generation produces asexual spores. The mature fern has true roots, leaves, and stem. Ferns growing in temperate climates have an underground stem called a rhizome that grows in a horizontal position. The rhizome not only stores food materials, but also gives rise to new fern plants that grow along its length. The stems of tropical species grow upright in a vertical position and serve as trunks of tree ferns.
Fertilization, birds Fertilization is accomplished during mating at which time the male and female place their cloacas close together. Sperm swim from the cloaca of the male into the female cloaca and up into the oviduct. Fertilization takes place high up in the oviduct before the albumen and the other surrounding membranes are secreted by the oviduct cells. Most birds lay a clutch of less than six eggs. However, ducks may lay as many as 15 eggs at one time. See Allantois.
Fertilization, fish Many sperm never reach the eggs and many fertilized eggs die before development. Hence there is an overproduction of gametes to ensure the survival of the species. In a few fish species fertilization is internal and parental care is given to the fertilized eggs. The stickleback male, for example, takes care of the fertilized eggs in nests and the male seahorse carries them around in a brood pouch.
Fertilization, frogs In frogs, fertilization is external. Sperm leave the testes through tubules called vasa efferentia that communicate with the kidney. The sperm cells then pass into the Wolffian duct that leads to the cloaca, a passageway that opens to the outside of the body. In the female, large egg masses are released into the body cavity from two ovaries, located at the anterior end of each kidney. Beating cilia sweep the eggs into coiled tubules known as oviducts where they are propelled to the cloaca and then out of the body. As the eggs pass through the oviducts they are coated with a thin layer of jelly-like material. At the time when the female is depositing eggs in the shallow waters of a pond or brook, the male deposits sperm over them. The sperm swim to the eggs and as each sperm reaches an egg, it digests its way through the jelly and into the egg, effecting fertilization. After fertilization the jelly coating on the eggs swells due to the absorption of large amounts of water. The swelling of the black jelly causes the eggs to adhere together and protects them from predation by fish and other animals. The fertilized egg, or zygote, undergoes cleavage, forming a tadpole.
Flagella and cilia Fine threads of cytoplasm that extend from the surfaces of some cells. Both of these structures are involved in the locomotion of some protist species. Cilia are relatively short extensions but appear in great numbers, usually surrounding the body of the protist. Flagella are much longer than cilia and appear in fewer numbers. In addition to serving the locomotive needs of one-celled organisms, flagella and cilia help functions of other types of cells. Sperm cells of animals and plants are propelled through fluid media by the whip-like actions of their flagella. Tissue cells of the human windpipe are lined with cilia that wave back and forth catching dust particles and pushing them away from the lungs. The microstructure of the flagella and cilia resembles that of the centrioles.
Flatworms The simplest of the flatworms demonstrate bilateral symmetry. This phylum represents a step up the evolutionary scale showing a recognizable head end and definite development of excretory, nervous, and reproductive systems. Most of the flatworms are hermaphrodites, as well as parasites. Some flatworms are serious parasites of humans and other animals. Among the flatworms are the planaria, flukes, and tapeworms.
Flower, parts of The reproductive structure of the angiosperm is the flower that encloses the male and female sex organs. The green leaflike sepals protect the flower when in the bud stage. Collectively, sepals are known as the calyx. Just inside of the calyx are colored petals. All of the petals in a flower are known as the corolla. The stamens are the male reproductive structures; pollen grains are produced in the anther. The pistil is in the center of the flower. The top portion of the pistil is the stigma. The style is the long stalk that leads to the rounded portion of the pistil called the ovary. Inside of the ovary are one or more ovules. The pistil and its many parts compose the female portion of the flower.
Flower, reproduction in Involves the maturation of the pollen grain during which three nuclei are produced. One is a pollen tube nucleus; the other two are sperm nuclei. As the sperm nuclei are traveling down the style, each ovule is going through a maturation process that results in the formation of a viable egg cell and a double nucleus. The sperm nuclei fertilize the egg cell and also the double nucleus. The zygote goes through a series of changes that lead to seed formation.
Fluid Mosaic Model See Cell membrane.
Food chain The flow of energy through an ecosystem can be studied by way of food chains which show how energy is transferred from one organism to another through feeding patterns. An example of a food chain on a cultivated field might be as follows: Lettuce --> Rabbit --> Snake --> Hawk The flow of energy in a food chain is in a straight line pattern. Most of the energy is concentrated in the level of the producer. At each succeeding level the energy is decreased. However, the feeding relationships among organisms in an ecosystem are not usually this simple, and, in actuality, are more complex, forming a food web.
Food pyramid Another way of illustrating energy flow in an ecosystem. The autotrophs at the base of the pyramid support all of the heterotrophs (consumers) that exist at each nutritional level and there is a decrease of available energy at each nutritional level.
Food web Shows that there are several alternative energy pathways in a food web. It is the alternative pathways that enable an ecosytem to keep its stability. One species does not eradicate another in the quest for food.
Fossils The preserved remains of plants and animals, usually found in sedimentary rock. The age of fossils is estimated by the use of carbon dating, the ratio of radioactive carbon (carbon 14) to nonradioactive carbon (carbon 12). The fossil records contained in the layers of sedimentary rock provide reliable evidence of change in plant and animal species. The lower down the rock layer, the older the fossil. Top layers contain more recent fossil remains of more complex species.
Fruit A ripened (mature) ovary bearing one or more seeds. A simple fruit develops from a single ovary; examples are tomatoes, plums, and pears. An aggregate fruit develops from a group of ovaries produced in a single flower; examples are raspberries and blackberries. A multiple fruit develops from the ovaries of a cluster of flowers that are carried on the same stalk; examples are pineapples, figs, and mulberries.
Fungi Eukaryotic, multicellular, and multinucleate organisms. Yeasts are unicellular forms. The cells of fungi are different from those of other species because the boundaries separating the cells are either entirely missing or only partially formed. Thus fungi are primarily coenocytic organisms; this means that the cells have more than one nucleus in a single mass of cytoplasm. However, the characteristic that most distinguishes the fungi from other organisms is their mode of nutrition. Fungi are saprophytes, absorbing organic nutritive matter from decaying plant and animal bodies.
Gametes Sex cells; male sex cells are called sperm and are produced in gonads called testes or spermaries. Female sex cells are the eggs or ova and are produced in female gonads called ovaries. All gametes have the haploid (monoploid) number of chromosomes.
Gametophyte In alternation of generations, the gametophyte generation produces haploid gametes. Fusion of the haploid gametes forms a diploid zygote, which grows into a sporophyte (plant). The sporophyte produces haploid reproductive spores. Each spore grows into a multicellular haploid plant, the gametophyte. The cycle repeats.
Gamma globulin A protein in the blood plasma from which antibodies are made. Antibodies, produced by the lymphocytes in the immune system, are molecules that inactivate or destroy antigens.
Ganglia (ganglion, sing.) Functional groups of nerve cell bodies that lie outside of the brain and spinal cord, allowing parts of the nervous system to coordinate activities without involving the whole system.
Gastrula A stage in embryonic development when the three primary tissue layers (ectoderm, mesoderm, and endoderm) develop and the primitive gut (archenteron) forms. See Cleavage.
Gene Around 1911, Thomas Hunt Morgan introduced the tiny fruit fly Drosophila melanogaster as the new experimental organism for work in the field of heredity. The experimental work of Morgan resulted in the discovery of the chromosome as the means by which hereditary traits are transmitted from one generation to another. Morgan's chromosome theory of inheritance includes the concept that chromosomes are composed of discrete units called genes. Genes are the actual carriers of specific traits and move with the chromosomes in mitotic and meiotic cell divisions. Morgan further proposed that genes control the development of traits in each organism. When genes change, or mutate, the traits they control change. Morgan's work was based on the chromosome theory of inheritance, which began to take shape in 1902 from the work of Walter S. Sutton.
Genetic code The DNA molecule carries coded instructions for controlling all functions of the cell. At the present time, scientists know most about the functions of the genetic code that control protein synthesis. They have determined that triplet combinations of bases code for each of 20 amino acids. The coded sequence of amino acids determines the formation of different types of proteins. The code for proteins is present in messenger RNA molecules that are complementary to DNA molecules. For example: let us suppose that a portion of a DNA molecule carries a code such as AAC GGC AAA TTT. Its mRNA complement would be as follows: UUG CCG UUU AAA.
Genetics The science of heredity.
Genome The complete store of an organism's genetic material, which consists of genes on chromosomes.
Genotype The genetic makeup of an individual. For a given trait an individual may have two like genes or two unlike genes. Genotype determines whether the dominant or recessive trait will show and whether or not the individual is dominant or recessive for the trait.
Geotropism Different parts of a plant may respond differently to the same stimulus. Thus the stem and leaves will grow upward, away from gravity; they show negative geotropism. On the other hand, the roots will grow downward, toward gravity; they show positive geotropism.
Germs Organisms that invade the body of animals and plants and cause disease. Organisms that cause disease are bacteria, spirochetes, viruses, and parasitic worms.
Gibberellin Plant growth substance isolated from the fungus Gibberella fujikuroi that has the following effects on plants:
1. It causes corn, wheat, and many other plants to grow very rapidly, showing an increase in height that is three to five times the normal in a short period of time.
2. It makes dwarf plants that by heredity should always be stunted, such as dwarf pea or dwarf corn, grow to the size of normal plants.
3. Seeds that are soaked overnight in it germinate ahead of time.
4. Biennial plants such as foxglove and carrot, that flower in the second year of their life cycle, burst into bloom in only one year.
5. Tomatoes and cucumbers develop from flowers that are not pollinated if the flower buds are sprayed with it.
6. Garden and house plants, such as geranium and petunias, bloom ahead of time, and have large flowers.
Glycogen A multibranched glucose storage polysaccharide deposited in the liver and muscles of animals; also known as "animal starch."
Glycolysis The anaerobic degradation of glucose into pyruvic acid; the initial stage of cellular respiration. See Anaerobic; Respiration.
Gonads The sex organs of male (testes) and female (ovaries). Sex cells (gametes) are produced in the sex organs. Male sex cells are called sperm; female, ova (ovum, sing.)
Grasshopper Belongs to a large group of organisms classified as arthropods. The name arthropod in literal translation means "jointed foot," a distinctive characteristic of this group, expressed traditionally as "jointed appendages." The arthropods are segmented animals protected by an exoskeleton made of protein and the flexible but tough carbohydrate chitin. The chitinous exoskeleton is fashioned in articulating plates held together by hinges covering both the body and the appendages, and attached to muscles that make possible quick and unencumbered movements.
Greenhouse effect The amount of carbon dioxide in the atmosphere has been found to be increasing. Much of this is coming from the burning of fossil fuels (coal, oil, and natural gas) by factories, homes, and automobiles. Since trees use carbon dioxide in photosynthesis, the cutting down of the world's forests over the years is preventing some of this C02 from being absorbed. The actual effects of this increase are not fully known. Some scientists claim that carbon dioxide, like the glass of a greenhouse, allows visible sunlight to pass through to the earth. As the earth warms up, it gives off infrared rays. These are absorbed by the carbon dioxide in the atmosphere, instead of being given off into space. It is believed that this "greenhouse effect," as it is called, will cause the earth's atmosphere to eventually warm up. Some of the possible effects of such an increase in atmospheric temperature might be: spread of desert areas; reduction of food crop production; warmer climate; melting of polar ice, with the raising of sea levels and the consequent flooding of heavily populated areas along the coast.
Growth Describes the increase of cell size and increase of cell numbers. The latter process occurs when cells divide in response to a sequence of events known as mitosis.
Guard cells Cells in the epidermis of the leaf that regulate the opening and closing of the stomates. See Leaf cross section.
Gymnosperms Gymnosperms are cone-bearers. They are woody plants, chiefly evergreens, with needle-like or scale-like leaves. Cone-bearing plants grow in many parts of the world including tropical climates. However, most species are found in the cooler parts of temperate regions. Examples of gymnosperm species are pines, spruces, firs, cedars, yews, California redwoods, bald cypresses, and Douglas firs. Most biologists think that the gymnosperms evolved directly from progymnosperms present during the Devonian period.
Haploid number The organism's sex cells, or gametes -- eggs and sperm, contain half the species number of chromosomes. This number is called the haploid number and abbreviated N. Meiosis is the kind of nuclear division that leads to the formation of sperm and egg cells.
Hardy-Weinberg principle A population includes all members of a species that live in a given location. Modern geneticists are concerned about the factors in populations that affect gene frequencies. All of the genes that can be inherited (heritable genes) in a population are known collectively as the gene pool. The Hardy-Weinberg principle uses an algebraic equation to compute the gene frequencies in human populations. The conditions set by the Hardy-Weinberg principle for determining the stability of a gene pool are as follows: large populations, random mating, no migration, and no mutation.
Heart The human heart lies in the chest cavity behind the breastbone and slightly to the left. The heart is a bundle of cardiac muscles specialized for rhythmic contractions and relaxations known as heartbeat. The rate of average heartbeat is 72 times per minute. The inside of the heart is divided into four chambers. The two chambers at the top are the receiving chambers, or the atria. The lower chambers, the ventricles, are pumping chambers. Each atrium is separated from the ventricle below by a valve. The atrium and the ventricle on the right are separated from the left atrium and ventricle by a thick wall of muscle called the septum.
Hemoglobin An iron-protein complex in red blood cells that functions as an oxygen carrier.
Heredity, Mendelian Gregor Mendel, an Austrian monk, began the first organized and mathematical study of how traits are inherited. Using the garden pea as the test organism, Mendel identified seven different traits that were easily recognizable in this self-pollinating plant. He called each of these traits unit characters. Mendel not only identified characteristics that seemed to be inherited, but for each unit character, he identified an opposite trait. For example: if the unit character was height, the opposite traits were short and tall. If the unit character was seed coat color, the opposite traits were yellow and green. Mendel formulated three major laws or principles of inheritance.
The Law of Dominance: If two organisms that exhibit contrasting traits are crossed, the trait that shows up in the first filial generation (F1) is the dominant trait. For example: when a pure-bred tall pea plant is crossed with a short pea plant, all of the offspring will be tall. The offspring will not be pure tall, however, and are therefore known as hybrids. The factor for shortness is hidden. We say today that the phenotype of the F1 plants is tall. A phenotype refers to the traits that we can see. The genotypes of genetic makeup of these plants is said to be hybrid or heterozygous, meaning mixed.
The Law of Segregation: When hybrids are crossed, the recessive trait segregates out at a ratio of three individuals with the dominant trait to one individual with the recessive trait. The 3:1 ratio is known as the phenotypic ratio, because it refers to the traits that can be seen and not those factors hidden in the germplasm. The hybrid cross is also known as the F1 cross and the offspring produced by this cross are known as the second filial generation or F2. In terms of modern knowledge, the F2 generation also produces another type of ratio called the genotypic ratio which refers to gene makeup. The genotypic ratio is 1:2:1, translated into 1 homozygous dominant (pure) individual: 2 heterozygous (hybrid) individuals: 1 homozygous recessive. Only the homozygous recessive shows the recessive trait.
The Law of Independent Assortment: Mendel believed that each trait is inherited independently of others and remains unaltered throughout all generations. We now know that Mendel's "factors" are genes that are linked together on chromosomes and that if genes are on the same chromosome, they are inherited together.
Hermaphrodite An animal that has both male and female reproductive organs and produces both eggs and sperm. Lifestyles such as burrowing (earthworms), living attached to objects (barnacles), or living within the body of another organism (tapeworms) make it difficult for such organisms to meet with a member of the opposite sex. Hermaphroditism solves the problem of reproduction. Most hermaphrodites mate with another member of the same species each donating sperm to fertilize the eggs of the other. Sequential hermaphroditism is a reproductive pattern exhibited in some reef fish that are able to change their sex from male to female or vice versa as conditions warrant.
Heterotroph An organism that cannot synthesize its food from inorganic materials such as carbon dioxide and water. A heterotroph must obtain its nutrition by the intake of preformed organic molecules. All animals are heterotrophs.
Heterotroph-autotroph hypothesis The first organisms on earth were probably heterotrophs utilizing the organic pool for nutrition. As time went on, the early heterotrophs must have faced a serious crisis because oxygen from photodissociation (atmospheric reactions) began to increase in concentration. This changed the atmosphere. Oxygen and hydrogen peroxide (H2O2) destroyed many heterotrophs. Eventually, photosynthetic organisms -- autotrophs such as blue-green algae -- evolved, increasing the oxygen content of the atmosphere and thereby threatening the continued existence of the heterotrophs. An ozone layer in the atmosphere developed from the high concentration of oxygen, which further diminished the organic compounds available to the beleaguered heterotrophs. Some heterotrophs developed pathways for utilizing oxygen in energy production (aerobic respiration). The carbohydrates produced by autotrophs and the oxygen of the atmosphere supplied the new heterotrophs with the nutritive materials necessary for survival (heterotroph-autotroph hypothesis). Thus the stage was set for the development of life on the scale that is known today.
Homeostasis The term used to describe the stable internal environment of the cell and the organism as a whole. Homeostasis is a condition necessary for life. The internal chemical balance of the cell must be maintained at a steady state to promote innumerable biochemical activities that foster the production and use of energy. The concept of homeostasis was initially developed by the nineteenth century physiologist Claude Bernard.
Homologous structures A comparative study of the bone structures and body systems of animals from the various phyla reveals a great deal of similarity. A comparative study of the skeletal systems of vertebrates shows that many of the bones are very much alike. Much of our evidence for evolution comes from a study of homologous structures. Homologous structures are bones that look alike and have the same evolutionary origin although they may be used for different purposes. The flipper of a whale, the arm of a human, and the wing of a bird are homologous structures having the same evolutionary origin and maintaining similarity of structure.
Hormones Secretions from the endocrine glands that regulate the activities of body organs. Examples: growth hormone regulates growth of the long bones; thyroxin regulates body metabolism; adrenaline controls the release of sugar from the liver. Hormones are secreted directly into the bloodstream, which then carries them to their target organs.
Hybrid An organism having mixed genes for a trait.
Hydra A freshwater coelenterate that is representative of a genus of the same name. Hydra is a polyp and has no medusa form in its life history. In length, each hydra is about 12 millimeters and has about eight tentacles that surround the mouth-anus. Hydras move about by somersaulting, end over end. The animal's locomotion is made possible by cells that have contractile fibers called myonemes. These epitheliomuscular cells have locomotor and sensory functions. Reproduction in hydra is sexual and asexual. A single organism produces both egg and sperm, which are discharged into the water where fertilization takes place. Asexual reproduction occurs by budding.
Hydrolysis See Digestion.
Hypothalamus The region of the brain that controls body temperature, osmoregulatory activities, maturity, thirst, hunger, and sex drive. The hypothalamus is also the region where the nervous and hormonal systems interact.
Immunity Ability to resist the attack of a particular disease-producing organism. Immunity to one kind of disease germ does not automatically make a person immune to other types of disease germs. Active immunity is brought about by antibody production by a person's own body cells. Active immunity can be stimulated in either of two ways; by getting the disease and recovering from it or by being immunized against the disease. Immunization that produces active immunity involves the injection of weakened disease agents that stimulate antibody production but produce only mild symptoms or none at all. Active immunity is longlasting because the body cells continue to produce the antibodies. An injection of gamma globulins can give a person temporary immunity against certain specific diseases. This means that a person has borrowed antibodies in the blood and not those made by his (her) own cells. This kind of immunity is called passive immunity. It lasts only as long as the antibodies last; when they are used up, the immunity ceases.
Infectious diseases Caused by pathogens (germs). These pathogenic microorganisms include certain bacteria, protozoans, spirochetes, richettsias, mycoplasmas, and fungi. Parasitic worms and viruses also often produce disease in humans. Most infectious diseases are contagious -- capable of being passed from one person to another by means of body contact or by droplet infection.
Ingestion The taking in or procuring of food. Digestion refers to the chemical changes that take place in the body by which nutrient molecules are converted to forms usable by cells.
Inheritance, intermediate Geneticists have discovered that in many cases a trait is not controlled by a single gene, but rather by the cooperative action of two or more genes. There are many instances in which Mendel's "law of dominance" does not hold true. A case in point is what was once called blending inheritance, or incomplete dominance. It is now known as codominance. When red-flowered evening primroses are crossed with white-flowered primroses, the hybrids are pink. Neither red nor white color is dominant and therefore the result is a blend. In sweet peas, the expression of red or white flowers is dependent upon two genes: a (C) gene for color and an (R) gene for enzyme. If C and R are inherited together, the flower color is red. If the dominant C is missing, the flower is white and if the dominant R is missing, the color is white. Therefore white flowers are the result of several different genotypes: ccrr, ccRR, CCrr, Ccrr.
Invertebrates Animals without backbones. About 90 percent of all animal species are invertebrates. Just like all members of the kingdom Animalia, invertebrates are multicellular. They are composed of cells that lack walls. Most invertebrates are capable of locomotion and have specialized cells with contractile proteins that facilitate movement. However, the adult forms of some lower invertebrate species are sessile, belonging to a group of filter feeders. These animals use cilia, flagella, tentacles, or gills to sweep smaller organisms from the currents of water that flow over or through their bodies into the digestive cavities. Some of the lower invertebrates reproduce vegetatively by budding. Other invertebrate species reproduce sexually, utilizing sperm and egg. Still other species reproduce asexually by parthenogenesis in which an unfertilized egg develops into a complete individual. Some invertebrates have marvelous powers of regeneration, the growing back of lost parts or the production of a new individual from an aggregate of cells or from a piece broken off from the parent organism. Examples of invertebrates are sponges, jelly fish, worms, clams, starfish, insects, crabs.
Involuntary muscle See Muscle, smooth.
Karyotype A technique of producing a photograph of matched chromosome pairs developed in 1956 by Joe Hin Tjio and Albert Levan.
Kidneys Paired organs of the human urinary system located dorsally in the abdomen. The kidneys reabsorb water, sodium, glucose, and some proteins. Excess water and the protein waste, urea, pass into the collecting duct and are stored temporarily in the urinary bladder until released from the body. See Urinary system.
Kingdom system of classification, five The largest and most inclusive classification category is the kingdom. For many decades, living things were considered to be either plants or animals and thus were grouped into one of the two established kingdoms. In 1969, the ecologist Robert Whittaker proposed an updated system of classification in which living things are grouped into one of five kingdoms, based on the extent of their complexity and the methods by which their nutritional needs are met.
Krebs cycle See Respiration.
Kwashiorkor A serious protein deficiency disease is kwashiorkor. This disease, which threatens the lives of many children in Africa, causes misshapen heads, barrel chests, bloated stomachs, spindly legs and arms, decreased mental abilities, and poor vision.
Leaf The most important function of green leaves is to carry out photosynthesis, the food-making process in which inorganic raw materials are changed into organic nutrients. A leaf consists of two parts: a stalk or petiole and the blade. The petiole attaches the blade to the stem. The blade is the place where photosynthesis takes place. Leaves vary greatly in shape.
Leaf cross section Study of a leaf cross section under the microscope reveals three types of tissue: upper and lower epidermis, mesophyll, and the vascular bundles. The mesophyll consists of palisade cells and spongy cells. The epidermis is a single layer of cells at the upper and lower surfaces of the leaf. The cells have thick walls made of cutin and lack chloroplasts. Their main function is to protect the underlying or overlying tissues from drying, bacterial invasion, and mechanical injury. On the underside of the leaf, the lower epidermis has pores known as stomates, the size openings of which are regulated by a pair of guard cells. The stomates serve as passageways for oxygen and carbon dioxide.
Legionnaires' disease An acute, pneumonia-like respiratory infection caused by an air-borne bacterium and associated with water in air conditioning towers. Symptoms are a feeling of malaise, chest pain, muscle aches, shortness of breath, and a dry cough. Other symptoms include a high fever, chills, abdominal pain, and sometimes abnormalities of the kidney and liver. If treated promptly with the antibiotic erythromycin, the infected person recovers. Without prompt treatment, the disease is fatal in 15 percent of cases.
Lichens Lichens are pioneer organisms that can inhabit bare rock and other uninviting substrates. They live on the barks of trees and even on stone walls. A lichen is a combination of two organisms -- an alga and a fungus -- that live together in a mutualistic relationship. The alga carries on photosynthesis, while the fungus absorbs water and mineral matter for its partner. The fungus also anchors the lichen to the substrate.
Life functions Living things are highly organized systems. They are self-regulating, self-reproducing, and capable of adapting to changes in the environment. To satisfy all of the conditions necessary for life, all living systems must be able to perform certain biochemical and biophysical activities which collectively are known as life functions. Nutrition is the sum total of those activities through which a living organism obtains nutrients (food molecules) from the environment. Life functions include nutrition as well as the processes of ingestion, digestion, and assimilation; respiration which encompasses breathing and cellular respiration; reproduction of cells; synthesis involving the biochemical processes of cells; regulation encompassing processes of control by hormones, enzymes, coenzymes, and utilized by the nervous system and the endocrine system; reproduction, both sexual and asexual.
Light reactions See Photosynthesis.
Linked genes Genes occurring on the same chromosome are inherited together. They are said to form linkage groups. Crossing over breaks linkage groups.
Lipids The lipids are a group of organic compounds that include the fats and fat-like substances. A lipid molecule contains the elements carbon, hydrogen, and oxygen similar to a carbohydrate. Unlike the carbohydrates, however, in lipid molecules the ratio of hydrogen to oxygen is much greater than 2:1. Most lipids are made up of two basic units: alcohol (usually glycerol) and a class of compounds called fatty acids.
Lock and key A simple analogy is used to explain the specificity of enzymes. Specificity refers to the characteristic of enzymes that permits a particular enzyme to form a complex with a specific substrate molecule only. The "lock and key" analogy explains enzyme specificity: the substrate is viewed as a padlock and the enzyme as the key able to unlock it. When unlocked (in the analogy) or acted upon by the key, the padlock comes completely apart. The key remains unchanged and ready to work again on another padlock of the same type.
Lungs The human body has two lungs. Each of these is enclosed in a double membranous sac known as the pleural sac. Not only is this sac airtight, but it also contains a lubricating fluid. The pleural sac and the lubricating fluid prevent friction that might be caused by rubbing of the lungs against the chest wall.
Lyme disease A flu-type disease transmitted from ticks to humans. The cause of the disease is a species of spiral bacteria injected in the human bloodstream through a bite by the infected deer tick, Ixodes dammini. Early treatment with antibiotics will prevent the development of arthritic symptoms. See also Health and Medicine.
Lymph The body cells are bathed with tissue fluid called lymph. Lymph comes from the blood plasma, diffusing out of the capillaries into the tissue spaces in the body. Lymph differs from plasma in that it has 50 percent fewer proteins and does not contain red blood cells. Lymph has the important function of bringing nutrients and oxygen to cells and removing from them the waste products of respiration.
Lymphocytes White blood cells that are produced in the lymph nodes and function in immune reactions of the blood.
Malpighian tubules These are long slender tubules, attached at one end to the digestive tract controlling excretion in insects and certain other arthropods. Nitrogen-containing wastes in the body fluid are changed into uric acid, which is then moved through the Malpighian tubule to the end of the digestive tract where it is ultimately excreted as dry crystals.
Mammals The characteristics that set mammals apart from other animals and made them adaptable to a wide range of habitats are as follows:
1. Mammals have mammary glands (from which the name mammal) that supply the young with milk directly after birth.
2. At some time during the life cycle, all mammals have hair.
3. Mammals are warm-blooded. Constant body temperature is due, in part, to the four-chambered heart, a device that prevents the mixing of oxygenated and deoxygenated blood.
4. Most species of mammals have sweat glands that provide a secondary means of excreting water and salts.
5. Mammalian teeth have evolved into three different types: incisors for tearing, canines for biting, molars and premolars for grinding.
6. All but a few species have seven vertebrae in the neck. These neck bones are known as cervical vertabrae.
7. A muscular diaphragm separates the thoracic cavity (containing the lungs and the heart) from the abdominal cavity (housing part of the digestive system, the reproductive organs, and the excretory system).
Marsupials The marsupials are primitive mammals that do not have a placenta. The young are about 5 centimeters long at birth and are in an extremely immature condition. At birth they crawl into the mother's pouch or marsupium. The rounded mouth is attached to a nipple and the mother expresses milk down the throat of the helpless fetus. As development occurs, the young marsupial is then able to obtain milk by sucking. There are 29 living genera of marsuspials, 28 of which live in Australia. The opossum Didelphys is indigenous to North, South, and Central America and Caenolestes inhabits regions of Central America only. Besides the opossum, other marsupials are the kangaroo, koala, Tasmanian wolf, wombat, wallaby, and native cat.
Mastigophora The Mastigophora are protozoa that have one or more flagella. Some species are free-living and inhabit fresh or salt water. Other Mastigophora species live in a symbiotic relationship with organisms of other species. For example, several species live in the intestines of termites, cockroaches, and woodroaches, where they digest cellulose for these insects. The genus Trypanosoma includes parasites that cause debilitating diseases in human beings. Trypanosoma gambiense is the zooflagellate that causes African sleeping sickness. Humans are infected with the trypanosome by the bite of an infected tsetse fly.
Meiosis Or reduction division, is cell division that occurs in the primary sex cells leading to the formation of viable egg and sperm cells. Meiosis reduces the number of chromosomes to one half in each gamete so that upon fertilization (the fusing of sperm and egg nuclei) the species chromosome number is kept constant.
Menstruation The process in which a nonfertilized egg is discharged from the body. The vascularized lining of the uterus, known as the endometrium, disintegrates in response to decreased levels of estrogen and progesterone in the blood. Menstrual bleeding lasts four to seven days in humans.
Messenger RNA The mRNA, carrying a code for a specific protein, moves from the nucleus to the cytoplasm. The mRNA attaches itself to several ribosomes, each having its own ribosomal RNA. Specific transfer RNA (tRNA) molecules bring to the ribosomes their own kind of activated amino acids. Transfer RNA molecules that fit the active sites of mRNA's on the ribosomes temporarily attach to them. As a result, amino acids are lined up in the proper sequence. The RNA code is a triplet code with one triplet, or codon, made up of three base coding for a specific amino acid. See also Protein synthesis.
Metabolism An inclusive term concerning all of the biochemical activities carried on by cells, tissues, organs, and systems necessary for the sustaining of life. Metabolic activities in which large molecules are built from smaller ones or in which nutrients are changed into protoplasm are called anabolic activities, or anabolism. Destructive metabolism in which large molecules are degraded for energy or changed into their smaller building blocks is called catabolic activity, or catabolism.
Metamorphosis The change from tadpole to adult frog is known as metamorphosis, a process controlled by the thyroid gland. The adult amphibian loses the gills, lateral line senses, tail, unpaired fins, and muscles controlling them -- the fish characteristics -- and develops structures adapted for life on land. An adult amphibian breathes by means of lungs and has a three-chambered heart that is more efficient at pumping blood between the lungs, heart, and rest of the body. In most species the adult has limbs for movement, but no tail.
Microscope, electron Magnification more than 200,000 times. Using electrons instead of light and magnets in place of lenses, the electron microscope has revolutionized the study of the cell. The scanning electron microscope has improved upon the resolution of fine detail made possible by electron microscopy. A fine probe directs and focuses electron beams over the material being studied, affording quick scanning and giving finer detail than is possible with the standard electron microscope.
Microscope, light The best light microscope is capable of magnifying objects 2,000 times. The phase contrast microscope makes transparent specimens visible, while the darkfield or the ultramicroscope gives vivid clarity to fragile and transparent organisms such as the spirochetes that cause syphilis. The ultraviolet microscope is used for photographing living bacteria and naturally fluorescent substances.
Mitochondrion A membranous cellular organelle. It consists of a smooth outer membrane and a folded inner membrane. The folds are called cristae. Like the cell membrane, the mitochondrion membrane is composed of proteins and phospholipids. The mitochondria are necessary for aerobic respiration to take place in cells.
Mitosis Mitosis (also known as karyokinesis) concerns the cell nucleus and its chomosomes. Before the onset of mitosis, the cell is in a stage known as interphase. During interphase, the chromosomes are exceptionally long and very thin, appearing as fine granules through the light microscope. It is during this stage that DNA molecules in the nucleus replicate. The result of replication is that each chromosome now has an exact copy of itself. When interphase comes to an end, the cell has enough nuclear material for two cells. The orderly process that divides the chromosomes equally between the two daughter cells is known as mitosis. There are four stages of mitosis: prophase, metaphase, anaphase, and telophase. The significant events that mark each of these stages and interphase are shown below:
Mollusks Soft-bodied, nonsegmented, and usualIy enclosed within a calcium carbonate shell. They are most abundant in marine waters, although some species inhabit fresh water and others live on land. All mollusks have a mantle, a flattened piece of tissue that covers the body and that may secrete the calcareous shell. The body of the mollusk is described as being a head-foot, a muscular mass having different shapes and functions in the various classes. The mollusks include the chitons, snails, clams, scallops, squids, and octopuses. This is one of the largest animal phyla and includes about 1,000 species.
Monera The monerans are prokaryotic cells. They lack a nuclear membrane, mitochrondria, endoplasmic reticulum, Golgi apparatus, and lysosomes. The prokaryotes do not have any membrane-bound organelles in the cytoplasm. The monera are unicellular organisms usually invisible to the naked eye. Most monerans live as independent cells, although some may occur in filaments (chains of cells) or colonies of cells held together by a gelatinous coat. This kingdom includes bacteria, blue-green bacteria, also known as blue-green algae.
Monotremes The monotremes are primitive egglaying mammals. The eggs, large and full of yolk, house the developing monotreme embryos. Examples of the monotremes are the "duckbill" or platypus (Ornithorhynchus) indigenous to Australia and Tasmania; the spiny anteater (Echidna), also an inhabitant of Australia; and a long snouted anteater (Proechidna) indigenous to New Guinea. Modified sweat glands of the anteater secrete a milk substitute that the young lick up from tufts of hair on the mother's belly.
Motor neuron See Nerve cell (neuron).
Muscle contraction Muscles contract due to a sliding filament mechanism. When the thick and thin filaments slide past each other, the Z lines of the sarcomeres are pulled closer together: in effect, contracting. Z lines form the boundary between sarcomeres. When the sarcomeres contract, the myofibrils contract, which causes the contraction of muscle fibers. Myofibrils are the basic units of muscle fibers. The figure illustrates the sliding filament mechanism of muscle contraction.
Muscular system Muscles represent 40 percent of the total weight of the human body. Muscle tissue is characterized by contractility and electrical excitability, two distinctive properties that enable it to effect movement of the body and its parts. There are three types of muscle tissue: smooth, striated, and cardiac.
Muscle, cardiac Cardiac muscle is present only in the heart, where the cells form long rows of fibers. Unlike other muscle tissue, cardiac muscle contracts independently of nerve supply since reflex activity and electrical stimuli are contained within the cardiac muscle cells themselves.
Muscle, smooth Smooth muscle is present in the walls of the internal organs, including the digestive tract, reproductive organs, bladder, arteries, and veins. Because smooth muscle is contained in organs that do not respond to the will of a person, these muscles are called involuntary muscles.
Muscle, striated Striated muscle is variously referred to as striped muscle, voluntary muscle, or skeletal muscle -- terms describing its structure and function. Located in the legs, arms, back, and torso, striated muscles attach to and move the skeleton; since they are moved by the will of the person, they are often termed voluntary muscles.
Mutations Genes can change and changes in genes are known as mutations. Mutations are usually recessive and they are usually harmful. Mutations usually occur at random and spontaneously. However, mutations may be induced by radiation or by chemical contamination. There are several types of mutations. A loss of a piece of a chromosome is known as a deletion. The genes on the broken off piece of chromosome are lost. Sometimes a broken piece of chromosome sticks on to another chromosome, thus adding too many genes; this type of mutation is known as duplication. Sometimes a piece of chromosome becomes rearranged in the chromosome where it belongs, thus changing the sequence of the genes on that chromosome; this is known as an inversion, and it prevents gene for gene matching when chromosomes line up during meiosis. Point mutations are changes in individual genes.
Natural selection Charles Darwin (1809-1882) was an English naturalist who together with his cousin, Alfred Russel Wallace (1823-1915), developed a theory of evolution that laid the groundwork for modern biological thinking. Darwin's theory of natural selection can be summed up thusly: large numbers of new plants and animals are produced by nature. Many of these do not survive because nature "weeds out" weak and feeble organisms by killing off those that cannot adapt to changing environmental conditions. Only the strongest and most efficient survive and produce progeny. Specific tenets of the Darwin-Wallace theory of evolution follow:
Overproduction: Every organism produces more gametes. If every gamete produced by a given species united in fertilization and developed into offspring, the world would become so overcrowded that there would be no room for successive generations. This does not happen because a balance is maintained in the reproduction of all species. Therefore natural populations remain fairly stable.
Competition: There is competition for life among organisms: competition for food, room, and space. Therefore there is a struggle for existence in which some organisms die and the more hardy survive.
Survival of the Fittest: Some organisms are better able to compete for survival than others. The differences that exist between organisms of the same species making one more fit to survive than another can be explained in terms of variations. Variations exist in every species and in every trait in members of the species. Therefore some organisms can compete more successfully for the available food or space in which to grow or can elude their enemies better. These variations are said to add survival value to an organism.
Nematodes See Worm-Parasites.
Nephridia Coiled tubules that serve as excretory organs in the segmented worms. The nephridia filter out waste materials.
Nephron The unit of structure and function of the kidney is the nephron. There are about one million of these microscopic units in each kidney. They actively remove waste products from the blood and return water, glucose, sodium ions, and chloride ions to the blood. The nephron is made up of several structures. The first of these is a knot of capillaries called the glomerulus. The glomerulus fits into a second portion -- the Bowman's capsule, a cup-shaped cellular structure that leads into the third part, the kidney tubule. There are four main parts of each kidney tubule: the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule, and the collecting duct.
Nerve cell (neuron) The basic unit of function of the nervous system is the neuron, or nerve cell. The parts of the nerve cell are the cyton, or cell body, the dendrites, and the axon. The dendrites receive signals from sense organs or from other nerve cells and transmit them to the cyton. The cell body passes signals to the axon, which then conducts the signals away from the dendrites and cell body. The axon terminating in end brushes (known also as terminal branches) is popularly called a nerve fiber. The nervous system has three types of neurons. Sensory or afferent neurons receive impulses from the sense organs and transmit them to the brain or spinal cord. Associative or interneurons are located within the brain or spinal cord. These transmit signals from sensory neurons and pass them along to motor neurons. Motor or efferent neurons conduct signals away from the brain or spinal cord to muscles or glands, so-called effector organs.
Nerve impulse Communication in the nervous system is made possible by signals or impulses carried in a one-way direction along nerve cells. These impulses are electrical and chemical in nature. When a neuron is not carrying an impulse, it is at resting potential. When a nerve cell is stimulated to carry an impulse, its electrical charge changes and it has an action potential. Action potentials (nerve impulses) from any one nerve cell are always the same. All impulses are of the same size, there being no graded responses. This is known as the "all or none response," meaning that a nerve cell will transmit an impulse totally or not at all.
Nerve net The simple nervous system in Hydra consisting of pointed sensory cells scattered throughout the endoderm and ectoderm, specialized to receive impulses.
Nervous system, autonomic A network of nerves known as the autonomic nervous system controls the body's involuntary activities and the smooth muscles of the internal organs, glands, and heart muscle. It is composed of motor (efferent) neurons leaving the brain and spinal cord and also of peripheral efferent neurons. The autonomic nervous system is divided into the sympathetic system and the parasympathetic system. These subsystems are antagonists. When one set of nerves activates the smooth muscles of the body, the other set inhibits the action. For example: the parasympathetic nerves dilate the blood vessels and slow the heartbeat; the sympathetic nerves constrict the blood vessels and quicken heartbeat.
Nervous system, human The human being has a complex nervous system that is composed of the principal functioning units of the central nervous system and the autonomic nervous system. The central nervous system is composed of the brain, spinal cord, and the nerves that radiate from the spinal cord. The brain is divided into three main parts: the forebrain, midbrain, and hindbrain. The forebrain controls all intelligent activities, voluntary muscle movements, speech, and interpretation of sensory data. The midbrain relays sensory information. The hindbrain controls all vital involuntary activities such as breathing, heartbeat, digestion, and the like. The central nervous system is the control center for all regulating activities in the body. See Brain.
Nitrogen cycle The cycle of events through which nitrogen in the air becomes useful to plants and subsequently to heterotrophic organisms.
Nodules Bumps on the roots of leguminous plants (beans, clover, alfalfa) that house nitrifying bacteria. The nitrifying bacteria convert ammonia, released into the soil by breakdown of proteins to nitrites and then to nitrates.
Nucleic acids DNA is an important part of the chromosome structure of all cells. DNA is a nucleic acid as is RNA. The unit of structure and function in the nucleic acid is called a nucleotide. A nucleotide is composed of a phosphate group, a five-carbon sugar, and a protein base. If the five-carbon sugar is ribose, the nucleic acid is ribonucleic acid (RNA). If the five-carbon sugar is deoxyribose, then the nucleic acid is deoxyribose nucleic acid (DNA). The protein bases in nucleic acids are ring compounds. Those bases with single rings are pyrimidines. Bases with double rings are purines. The pyrimidines in nucleic acid are thymine, cytosine, and uracil. The purines are adenine and guanine. The four bases that make up the DNA molecule are adenine (A), guanine (G), thymine (T), and cytosine (C). The four bases that make up the RNA molecule are adenine (A), guanine (G), cytosine (C), and uracil (U).
Nutrition Is the totality of methods by which an organism satisfies the energy, fuel, and regulatory needs of its body cells. Those substances that contribute to the nutritional needs of cells are the nutrients. Animals take these nutrients into the body by the ingestion of food. Food, therefore, refers to edible materials that supply the body nutrients. Nutrients needed in large amounts are classified as macronutrients: carbohydrates, proteins, and fats. Micronutrients -- vitamins and minerals -- are needed in smaller amounts. Vitamins are organic compounds; minerals are inorganic. Malnutrition results from the improper intake of nutrients.
Nutritional relationships When two different species of organisms live together, the relationship is called symbiosis. If the relationship is of mutual benefit to both species, it is called mutualism. When one species benefits and the other does not but is not harmed by the association, the condition is known as commensalism. When one species lives at the expense of another, doing harm to its host, the relationship is parasitism. Disease-producing organisms are parasites.
Obligate aerobes Most species of the eubacteria are aerobic, using molecular oxygen in the process of breaking down carbohydrates to carbon dioxide and water. Obligate aerobes are those organisms that can live only in an environment that provides free or atmospheric oxygen. An example of an obligate aerobe is Bacillus subtilis.
Obligate anaerobes Some bacteria are obligate anaerobes and derive their energy by fermentation. These organisms cannot live in an environment of free oxygen. Many obligate anaerobes are disease producers; included in this group are Clostridium tetani, the causative organism of tetanus, and Clostridium botulinum, the bacterium that induces food poisoning. Still other bacteria are facultative anaerobes. These are basically aerobic bacteria, but they can live and grow in an environment that lacks free oxygen.
Oogenesis The maturation of the egg cell in which the primary oocyte (egg cell) goes through reduction division (meiosis). The outcome of these divisions is the production of one viable egg cell and two or more polar bodies.
Open circulatory system Characteristic of mollusks and the arthropods such as the grasshopper in which the blood is not confined in blood vessels and has contact with body tissues.
Organelles Organized structures that are parts of cells, such as ribosomes, nuclei, mitochondria, chloroplasts, cilia, contractile vacuoles, and endoplasmic reticulum.
Organs Are groups of tissues that work together to carry out a special function. Examples of organs are the heart, lungs, liver, and stomach.
Osmosis Is the diffusion of water through a membrane. Osmosis is a form of passive transport.
Ovary Is the female gonad where egg cells (ova) are produced. At times the ovary produces hormones and thus functions as an endocrine gland.
Oviparous Egg-laying, as in birds.
Ovoviviparous A condition in which eggs develop but are retained and hatched inside the mother's reproductive tract, as in cartilaginous fish (sharks) and a few snakes.
Ovulation The release of an egg cell (ovum) from a follicle in the ovary. Within the follicle a mass known as the corpus luteum forms in mammals and secretes the hormone progesterone. If the egg is not fertilized, the corpus luteum disintegrates and an egg is released from another follicle during the next menstrual cycle.
Ovules Immature seeds contained within the ovary of the flower.
Paramecium Representative of the ciliata. The cytoplasm in ciliates is differentiated into rigid outer ectoplasm and a more fluid inner endoplasm. A pellicle lies just inside of the cell membrane. Some species respond to adverse environmental stimuli by discharging elongated threads called trichocysts that serve as defense mechanisms or a means of anchoring the protist to floating pond material while feeding. Characteristic of the ciliata is the presence of two kinds of nuclei. The macronucleus controls metabolic activities, while the smaller micronucleus directs cell division. The figure shows the structure of the paramecium, a typical representative of the ciliata.
Parasites An organism that lives on or inside of the body of a plant or animal of another species and does harm to the host. Parasites offer physical discomfort to the host and tend to kill slowly, meanwhile having had time to reproduce themselves for several generations. Ectoparasites live on the host's body; body lice, dog fleas, ticks. Endoparasites live within the host's body and exhibit several adaptations for life in an intestine or in muscle or blood.
Parthenogenesis Although an egg will not develop unless it has been fertilized by sperm, some lower animals reproduce by parthenogenesis -- in which eggs develop without sperm. This is true of aphids, or plant lice, water fleas, and others. In bees the drone, or male, develops from an unfertilized egg. Artificial parthenogenesis has been accomplished by scientists experimenting with the eggs of sea urchins and frogs. Jacques Loeb stimulated frog eggs to go through cleavage and eventually to form frogs without fertilization by sperms; he used various stimuli, such as pricking the membrane with a needle, and treatment with salt solutions or acids. Dr. Gregory Pincus was successful in producing "fatherless rabbits" by removing the ova from female rabbits, treating the ova with salt solutions and implanting them in other female rabbits. The baby rabbits that developed were females, and were subsequently mated to produce normal offspring.
Parturition The birth process is known as parturition. In humans the period of gestation (period of embryo development) is about 9 months or 40 weeks. At the end of that time, the uterus begins to contract in a process called labor to expel the baby. The onset of uterine contractions is probably caused by the release of oxytocin into the bloodstream by the posterior pituitary. The human newborn passes through the neck of the uterus (cervix) head first and then through the vagina to the outside.
Perennials Plants that live for many years, such as trees, shrubs, and grasses. Fire, disease, and mismanagement by humans causes the death of perennials.
pH The number of hydrogen ions in a solution is the basis of pH. The pH scale ranges from 0-14. A pH of 7 is neutral. Below the pH of 7, the number of H+ ions increases and the solution becomes more acidic. The lower the pH number, the stronger the acid. A pH above 7 indicates that there are more OH- ions than H+ ions and the solution becomes more alkaline. Blood has a pH of 7.3. Special indicators are used to show the acidity or alkalinity of a solution.
Phagocytosis A process by which a cell first surrounds and engulfs a particle and then ingests it. Solid particles are ingested by cells through a process known as phagocytosis. White blood cells ingesting bacteria serve as an example of phagocytosis.
Phenotype The traits of an organism that can be seen.
Phloem Water-carrying (vascular) tissue in the plant leaf and stem specialized for conducting water with dissolved nutrient molecules downward to the root.
Photoperiodism The physiological response made by plants to changes in day length is known as photoperiodism. Some plants (short-day) flower only if they are exposed to light for less than a certain amount of time each day, other plants (long-day) must have a certain minimum length of photoperiod. Researchers explain the ability of plants to measure time by the action of phytochrome, a light absorbing pigment that is associated with the cell membrane and with some of the cell's internal membranes.
Photosynthesis Photosynthesis takes place inside of chloroplasts, structures within the cells of the leaf. Chloroplasts have fine structures within -- flattened membranous sacs named thylakoids. On the membranes of the thylakoids, chlorophyll and the accessory pigments are organized into functional groups known as photosystems. Each of these photosystems contains about 300 pigment molecules that are involved directly or indirectly in the process of photosynthesis. Photosynthesis involves four sets of biochemical events: photochemical reactions, electron transport, chemiosmosis, and carbon fixation. The photochemical reactions and electron transport activities take place on the membranes of the thylakoids. The oval membranes of a thylakoid surround a vacuole or reservoir in which hydrogen ions are stored until needed in the Calvin cycle, or carbon fixation. Each thylakoid rests in the stroma or ground substance of the chloroplast. The stroma is the place where carbon fixation occurs.
Pinocytosis Cell drinking. The engulfing of molcules in solution through the cell membrane requiring the use of the cell's energy.
Plants, green Green plants are grouped in the kingdom Plantae. Members of the kingdom Plantae contain the green pigment chlorophyll. Not only does chlorophyll color plant leaves and some stems green, it, more importantly, traps light energy which is used in the process of photosynthesis. As an outcome of photosynthesis nutrient molecules are made, serving as food for both plants and animals. Most species of the kingdom Plantae are nonmotile, anchored to one place, and unable to move about, but a few of the lower plants are motile for at least part of the life cycle. However, the evolutionary trend exhibited in green plants is toward stationary organisms that carry out their life functions on land in locations where they remain for life. Lower plant species equipped to swim live in salt and fresh water. Higher plants are terrestrial (land-dwelling)
Pollination The transfer of pollen from the anther to the stigma. Most flowers are insect- or wind-pollinated. Insect-pollinated flowers have petals and nectar that attract insects. The pollen tends to be sticky and clings more easily to insect bodies. Wind-pollinated flowers lack petals; or if present, they are relatively inconspicuous. They seldom produce nectar. Pollen is light and dry and sometimes has membranous appendages, all these characteristics making it easier to become wind-borne. Windblown pollen is produced in large quantities enhancing the chances for pollination.
Polymorphism The honeybee exhibits a specialized social structure called polymorphism, a condition in which individuals of the same species are specialized for different functions. In a honeybee colony, three classes of individuals arise: fertile males called drones; fertile females, or queens; and sterile females, or workers. The workers have a special concave surface on the second pair of walking legs called a pollen basket used to carry pollen. The queen bee receives sperm from the drone once during her lifetime. The sperm are stored in a special organ called the spermatotheca in which they may live for years. Fertilized eggs give rise to females, most of which remain workers. A special female may be selected by the colony and fed a diet of "royal jelly" that causes her to grow larger than the others and become fertile. This fertile female will become a queen, and either take over the existing colony or start a colony of her own. Drones develop from unfertilized eggs by the process of parthenogenesis.
Population genetics See Hardy-Weinberg principle.
Predation This is the process of one species feeding upon another. The predator is the consumer that seeks out the prey to be consumed. Predators have special adaptations that enable them to hunt and catch their food supply: speed and agility, stingers, fangs, poisons, claws, and camouflage. Plant species have certain adaptations that protect them against predation such as thorns, microscopic spines, and the production of poisons such as nicotine, morphine, strychnine, mescaline, and aromatic compounds such as cinnamon and cloves. Animal defenses against predation include protective coloration, spines of the porcupine, the odor of the skunk, and the ability to hide through camouflage.
Proteins Complex molecules built from amino acids. About 20 amino acids are essential to living systems. From these a large number of different kinds of proteins are formed. The great variety of protein molecules is possible because of the many ways in which amino acid molecules can be arranged. Changing the sequence of just one amino acid in a chain will change the protein molecule. Much of the work of the cell is concerned with the synthesizing of protein molecules. Some of these proteins such as hormones, enzymes, and hemoglobin are used in complex biochemical activities. Other proteins contribute to the structure of cells such as those that make up the plasma membrane and other cellular membranes.
Protein synthesis The code for proteins is present in messenger RNA molecules, which are complementary to DNA molecules. For example: let us suppose that a portion of a DNA molecule carries a code such as AAC GGC AAA TTT. Its mRNA complement would be as follows: UUG CCG UUU AAA. The mRNA, carrying this code, now moves from the nucleus to the cytoplasm. The mRNA attaches itself to several ribosomes, each having its own ribosomal RNA. Specific transfer RNA (tRNA) molecules bring to the ribosomes their own kind of activated amino acids. Transfer RNA (tRNA) molecules, each with a particular amino acid attached, attach temporarily to the codons on the mRNA and their amino acids are linked together in the correct sequence, one amino acid at a time. Note that the RNA code is a triplet code with one triplet, or codon, made up of three bases coding for a specific amino acid. See also Messenger RNA.
Protists All of the species assigned to the kingdom Protista are eukaryotic, for example, Amoeba and Paramecia. Most protists carry out their lives within a single cell as free-living organisms. However, some protist species are organized into colonies where each cell carries out its own life functions and where, also, there may be some simple division of labor among the cells in the grouping. An impressive variety of species are classified as protists, and they probably descended from diverse evolutionary lines. The protists themselves represent evolutionary modification and are probably the ancestors of the modern fungi, plants, and animals.
Protozoa Protozoa, meaning "first animals," are one-celled heterotrophs. Species of protozoa number in the thousands. They live in fresh water, salt water, dry sand, and moist soil. Some species live as parasites on or inside of the bodies of other organisms. Reproduction in the protozoans is usually described as being asexual by means of mitosis, but recent research has revealed that many protozoa augment asexual reproduction with a sexual cycle. Usually, the sexual cycle occurs during periods of adverse environmental conditions, and the cell arising from the fusion of gametes (zygote) can resist unfavorable conditions. The thick wall and the decreased metabolic rate of the cyst permits survival during periods of cold, drought, or famine. The protozoa are divided into four phyla, based primarily on the methods of locomotion.
Punctuated equilibrium There is a time frame for evolution. The concept of gradualism supports the idea that evolutionary change is slow, gradual, and continuous. The concept of punctuated equilibrium sets forth the idea that species have long periods of stability, lasting for four or five million years, and then change as the result of some geological or other environmental change.
Punnett square A Punnett square is a diagrammatic device used to predict the genotypic and phenotypic ratios that will result when certain gametes fuse. Remember that as a result of meiosis each gamete has only one half the number of chromosomes that are in the somatic cells.
Problem: In fruit flies, long wing (L) is dominant over vestigial wing (l). What is the result of a cross between two flies that are heterozygous (Ll) for wing length?
Solution: Parents: Male x Female Ll Ll Gametes: L l L l Punnett square: L l L LL Ll l Ll ll F2: LL = 1 homozygous dominant long winged fly Ll = 2 heterozygous dominant long winged flies ll = 1 homozygous recessive short winged fly
Race All humans belong to the species Homo sapiens. This means that the genetic material of all people is so similar that all humans can interbreed and produce fertile offspring. The human species is really a group of interbreeding populations. Populations that have adapted to certain environments become genetically different based on the frequency with which certain genes appear. Skin color, hair texture, body build, and facial bone structure are a few of the characteristics that identify human population groups known as races. Although we can make broad generalizations about the identifying characteristics of racial groups, not every member of each group fits these specifications. A set of physical characteristics can be drawn up that will fit individuals of several different races. Therefore, it is difficult for biologists and anthropologists to agree on the number of human races.
Radioactive dating Scientists have determined that certain elements disintegrate by giving off radiations spontaneously and at a regular rate. Such elements are said to be radioactive. In the process of emitting radiations, the radioactive substance changes to something else. For example: uranium-238 changes to lead. The half-life of U-238, the rate at which one half of the uranium in a rock sample will change to lead, is 4.5 billion years. Uranium's rate of decay is not affected by any chemical or physical conditions. Therefore measuring the uranium-lead ratio in a sample of rock is a very reliable method for estimating the age of the rock. Dating of the oldest rocks found on earth indicates that they are about 3 billion years old. To allow time for the original formation of the rocks, geologists add another 2 billion years to this figure, thus arriving at the 4.5-5 billion-year estimate of the age of the earth.
Recessive trait A characteristic that will appear if there are two like (recessive) genes for the trait. A trait that is masked by a dominant gene. For example: in sheep, white wool is dominant over black wool. A sheep with black wool must have two recessive genes for the trait.
Recombinant DNA Recombinant DNA is DNA combined from two different organisms to produce characteristics not found in nature. The technique for doing this involves the use of a class of special enzymes called "restriction enzymes." These enzymes have the ability of splitting a DNA strand. The fragments of DNA have sticky ends, and when they touch a strip of DNA from another organism, they stick to it. In this way new genes can be introduced into an organism. Once done, the cell can synthesize the protein coded for by the newly acquired genes. Some proteins that have been produced in this way are interferon, insulin, and human growth hormone.
Red blood cells (Erythrocytes) The human body contains about 25 trillion erythrocytes, each one lasting about 120 days. New red cells are produced by the bone marrow at the rate of one million per second. Erythrocytes contain hundreds of molecules of the iron-protein compound hemoglobin. In the lungs, oxygen binds loosely to hemoglobin forming the compound oxyhemoglobin. As erythrocytes pass body cells with low oxygen content, oxygen is released from hemoglobin and diffuses into tissue cells. Carbon dioxide combines with another portion of the hemoglobin molecule and is transported to the lungs where it is exhaled.
Reflex If you accidentally touch a flame, your finger is automatically pulled back. A sensory neuron carries the impulse from the receptor, at the end of your finger, to the spinal cord, here an associative neuron receives it and sends it over a motor neuron to a muscle in your arm, which contracts, and pulls your finger away. There is no thought involved in the reaction. It is centered in the spinal cord. A moment later, you are aware of it, because impulses are sent up the spinal cord to the brain. Fortunately you do not have to think about such stimuli. The response is inborn and is a factor in your survival. Such a reflex protects you.
Regulation Encompasses all processes that control and coordinate the many activities of a living thing. Chemical activities inside of cells are controlled by enzymes, coenzymes, vitamins, minerals, and hormones. The nervous and endocrine systems of higher animals integrate and coordinate body activities. Growth and development of plants is regulated by auxins and other growth-control substances. Gene activity is regulated by special molecules that turn the gene on and off.
Replication The process through which a DNA molecule makes an exact duplicate of itself.
Reproduction The process by which new individuals are produced by parent organisms. Basic to the understanding of reproduction is the concept that organisms produce the same kind of individuals as themselves. There are two major kinds of reproduction: asexual and sexual.
Reproductive system, female The female reproductive system serves three important functions: the production of egg cells, the disintegration of nonfertilized egg cells, and the protection of the developing embryo. The reproductive system has specialized organs to carry out these functions. Two oval-shaped ovaries lie one on each side of the midline of the body in the lower region of the abdomen. On a monthly alternating basis each ovary produces a mature egg. Eggs are located in spaces in the ovary called follicles. As an egg matures, it bursts out of the ovarian follicle and is released into the appropriate branch of the fallopian tube, a tube that leads from the region of the ovary to the uterus. If the egg is fertilized, it becomes implanted in the uterus where it goes through a series of cell divisions known as cleavage.
Reproductive system, male In the male reproductive system some organs are located outside of the body and others are positioned internally. The scrotum contains the testes, glands that produce sperm, and the male hormone testosterone. Also positioned outside of the body is the penis, the organ that delivers the sperm into the body of the female. Each testis contains thousands of seminiferous tubules. Within these tubules, the sperm cells are manufactured. Each epididymis tubule functions as a storage place for sperm and also serves as a pathway that carries the sperm to a duct called a vas deferens. In its travels to the vas deferens, the sperm pass the seminal vesicles where they obtain nutrients. From the vas deferens, the sperm are conducted to the urethra, a single tube that extends from the bladder through the penis. Sperm cells leave the body through the penis. See Sperm.
Reptiles Reptiles have a dry leathery skin covered with epidermal scales. A somewhat flattened skull contains a brain having a cerebrum much larger than that of the fish or amphibians. The eyes have secreting glands that keep the surface moist. Reptiles are air-breathers and have rather well-developed lungs. The heart is composed of two atria and a ventricle; in some species the ventricle is almost divided into two compartments, an evolutionary signpost pointing to the four-chambered heart. The body temperature of reptiles is not constant, changing with the external environment. In popular speech, such animals are called cold-blooded; in technical language, poikilotherms or ectothermic.
Respiration Consists of breathing and cellular respiration. Breathing refers to the pumping of air into and out of the lungs of air-breathing animals or the movement of water over the gills of fish. During breathing, oxygen diffuses into the air sacs in the lungs and carbon dioxide moves out of the lungs through the nose and mouth. Cellular respiration is a combination of biochemical processes that release energy from glucose and store it in ATP (adenosine triphosphate) molecules.
Respiratory system The respiratory system includes the structures through which oxygen comes into the body to reach the bloodstream, and through which carbon dioxide and water vapor leave. Summary of route of air through respiratory system: (1) nostrils, (2) nasal cavity and sinuses, (3) pharynx, (4) larynx, (5) trachea, (6) bronchi, (7) bronchial tubes in the lungs, (8) air sacs (alveoli).
Retrovirus A virus in which the genetic information is coded in ribonucleic acid (RNA) instead of in deoxyribonucleic acid (DNA). HIV, the virus of AIDS, is a retrovirus that produces reverse transcriptase, an enzyme that enables the retrovirus to replicate, and to make more of itself.
Ribonucleic acid (RNA) A nucleic acid consisting of a large number of nucleotides, each of which contains ribose sugar and four bases, including uracil, and a phosphate radical. See also Protein synthesis.
Ribose A sugar of chemical formula C5H10O5: one of the building blocks of nucleic acid.
Ribosome A small organelle that is the site of protein synthesis.
Rickettsiae The rickettsiae are very small Gram negative intracellular parasites. They were first described in 1909 by Harold Taylor Ricketts, who found them in the blood of patients suffering from Rocky Mountain spotted fever. The rickettsiae are nonmotile, nonspore forming, nonencapsulated organisms. In length, these organisms range from 0.3-1 micrometers. They live in the cells of ticks and mites and are transmitted to humans through insect bites. The rickettsiae are responsible for several febrile (fever-producing) diseases in humans, such as typhus fever, trench fever, and Q fever.
Roots Roots anchor plants to the soil and absorb water and dissolved minerals from the ground. The absorbed materials enter the root by way of root hairs which are one-cell extensions of the epidermis. From the root hairs, dissolved materials pass through the cortex, endodermis, and pericycle into xylem cells. The xylem cells conduct the dissolved materials upward. The root cortex serves in the storage of food and water.
Saprophytes (saprobes) These organisms obtain their food by absorbing nutrients from dead organic matter. Examples are some species of eubacteria and species of fungi. The fungus has specialized structures that secrete digestive enzymes into the food substrate on which they live, such as dead logs. The digestive enzymes liquefy the small portions of the log, releasing organic molecules that are absorbed by the fungus. Saphrophytic bacteria secrete digestive enzymes onto the food substrate for digestion. The released organic molecules then are absorbed by the bacteria.
Scientific method Scientific problem solving depends upon accuracy of observation and precision of method. Inherent in scientific thinking is orderliness of approach, which invites the forming of conclusions from hypotheses, theories, principles, generalizations, concepts, and laws. Scientific problem solving follows a pattern of behaviors that are collectively known as the scientific method.
Semi-permeable membrane The cell membrane controls the passage of materials into and out of the cell. It is often referred to as a living gatekeeper. The cell membrane is semi-permeable and highly selective: not every ion or molecule can cross its boundary. The movement of materials across the cell boundary and into or out of the cell is given the general term of transport. It is controlled by the globular proteins, phospholipids, and pores of the membrane and by the electrochemical nature of protoplasm, the living substance of the cell.
Sense organs The human body has five major senses -- sight, hearing, taste, smell, and touch -- that provide information about the external environment and transmit the stimuli to sensory nerves and ultimately to the brain for processing.
Sex determination In human beings, there are 22 pairs of autosomes, chromosomes that affect all characteristics not involved in sex determination. One pair of chromosomes determines the sex of an individual. In normal females, the sex chromosomes are designated as XX. In normal males, the sex chromosomes are XY. Certain disorders are sex-linked, usually passed from mother to son by a defective gene on the X chromosome; red-green color blindness is one such sex-linked trait that is found more frequently in males and hardly at all in females. Hemophilia is another sex-linked trait that affects males with greater frequency than females.
Sharks Cartilaginous fish in which the skeleton is made of cartilage instead of bone. The body of the shark is covered with placoid scales which arise from the ectoderm, also forming teeth in the jaws and on the roof of the mouth. Sharks have no swim bladder and the gill slits are uncovered. The fertilization is internal; the embryos are nourished from food from the egg.
Sinoatrial node Each heartbeat is started by self activating electrical activity of the heart's pacemaker known as the sinoatrial node (S-A node), positioned in the wall of the right atrium. From the S-A node, the impulse spreads throughout the atrium to the antrioventricular node (A-V node), a specialized bundle of cardiac muscle located on the atrium near the ventricles. The impulse spreads from the A-V node to all parts of the ventricles causing simultaneous contractions in the ventricles.
Skeletal system The human skeleton, like that of all vertebrates, is a living endoskeleton that grows with the body. At birth, the human baby has a body that is made up of 270 bones. Due to the fusion of separate bones, the mature skeleton is composed of 206 bones. The human skeleton is a magnificent feat of engineering. The primary purpose of the skeleton is to carry the weight of the body and to support and protect the internal organs. The skeleton must be strong and able to absorb reasonable amounts of shock without fracturing. At the same time, the body framework must be flexible and light enough in weight to permit movement. Skeletal bones move in response to muscles that work like levers, allowing a variety of movements such as walking, running, hopping, sitting, bending, lifting, and stooping.
Slime molds Slime molds live on the forest floor where they grow in damp soil, on or around rotting logs and on decaying vegetation. They appear to be shapeless globs of slime of varying colors: white, yellow, or red. The life cycle includes either an amoeboid slime mass called a plasmodium or a plant-like sporangia stage that is supported by stalks called fruiting bodies. A multicellular mass is called a plasmodium. A multinucleated mass is called a pseudoplasmodium. The diagram above shows stages in the life cycle of true slime mold.
Sodium-potassium pump At times molecules are forced out of cells by exocytosis, a means by which they are carried to the cell surface by vacuoles or vesicles. The sodium-potassium pump is a means by which excess sodium ions are forcibly extruded from nerve cells while potassium ions are pulled into the cell.
Species The basic unit of classification is the species. A species is a group of similar organisms that can mate and produce fertile offspring. The red wolf, African elephant, red oak, house fly, hair cap moss -- each belong to a separate and distinct species. For example, the red wolf belongs to the red wolf species in which the male mates with the female and produces fertile red wolf offspring. Upon maturity these red wolf offspring will reproduce just as their parents did. Species is a reproductive unit, not one defined by geography. Once brought together, a Mexican male Chihuahua can mate with a female Chihuahua born in France because they are species compatible. In rare instances, members of closely related species -- horses and donkeys, for example -- can mate and produce offspring. But the products of interspecies matings are not fertile and therefore cannot reproduce. When a male donkey mates with a female horse (mare), a mule is produced. The mule is an infertile hybrid. The mating of a male horse (stallion) and a female donkey results in a hinny, also an infertile hybrid.
Sperm The male gamete is structured for motility. It leaves the male reproductive system and is able to swim through the female reproductive system where it may fertilize (penetrate) an egg cell. Sperm cells are haploid, having half the number of chromosomes of a fertilized egg.
Spirochetes Most bacteria belonging to this group are anaerobic; many are disease producers. These bacteria are long, thin, and curved, moving with a wriggling, corkscrew-like motion, made possible by an axial filament. In some ways, the spirochetes resemble protozoa, but they are nonnucleated. They do not form spores or branches. They reproduce by transverse fission. The spirochete Treponema pallidum causes syphilis.
Spongy cells See Leaf cross section.
Sporozoa The Sporozoa are parasitic spore-formers. The adult forms are incapable of locomotion, although immature organisms may move by means of pseudopodia. Some species of sporozoa go through a complicated life cycle requiring different hosts during different life stages. For example, the species Plasmodium vivax -- the agent that causes malaria -- requires two hosts: the Anopheles mosquito and a human.
Starfish The starfish is an excellent representative of the echinoderms. It has all of the distinguishing characteristics: pentaradial symmetry, spiny skin, tube feet controlled by a water vascular system, no head, excretory or respiratory system. Protruding from the wall of the coelom and extending out between the calcareous plates into the sea water, are the papulae, sac-like structures that function as respiratory and excretory organs. The mouth is located in the center of the disc on the underside of the body. The nervous system is composed of a nerve ring located in the disc from which a ventral and radial nerve branch into each arm. Starfish sexes are separate. Starfish have remarkable powers of regeneration. If an arms breaks off, the arm grows back. Should a piece of the central disc be attached to the amputated arm, a new individual will grow from the dismembered part. Starfish prey on oysters.
Stem See Woody stems.
Stoma or stomate Small pore in the plant epidermis that permits gas exchange. Each stoma is bounded by a pair of guard cells whose osmotic status regulates the size of the opening.
Substrate The molecules on which an enzyme exerts catalytic action. The surface that supports any organism. See Enzyme-substrate complex.
Synthesis Involves those biochemical processes in cells by which small molecules are built into larger ones. As a result of synthesis, amino acids, the building blocks of proteins, are changed into enzymes, hormones, and protoplasm.
Tadpole See Fertilization, frogs.
Tapeworm The life cycle of the tapeworm includes two hosts. A mature proglottid contains a sac filled with hundreds of fertilized eggs. When the proglottid walls rupture, the ground becomes infected with fertilized eggs. If these eggs are ingested by a pig, the protective walls surrounding each egg are digested, releasing developing embryos of the tapeworm into the digestive system of the pig. These embryos bore into the pig's capillaries and are carried by the blood to the muscles where the scolex forms a cyst. The worm now remains encysted in the muscles (meat) of the pig. If the butchered pig (now called pork) is improperly cooked and eaten by a human, the encysted worm becomes activated. Its head begins to bud proglottids and the cycle of infection repeats.
Taste buds The taste buds, which receive stimuli for the four taste sensations of sweet, sour, bitter, and salty, are located in different parts of the tongue. The senses of taste are related to that of smell. When we have a bad head cold, or hold our nose, taste is affected.
Testes Male gonads that produce sperm, the male sex cells. Each gonad consists of tightly coiled seminiferous tubules where sperm production begins.
Thallophyta Most algae are not differentiated into roots, stems, and leaves. The simple body of the plant -- either a single cell or a flat sheet of simple cells -- is known as a thallus. Thallophytes do not have specialized tissues to carry water, anchor the plants, or to grow new cells. As a rule, the sex cells of the thallophytes are produced in rather simple sex organs that are not protected by a surrounding wall of cells. The zygotes of the thallophytes do not develop into embryos that are contained in a female reproductive organ. Most species of thallophytes live in fresh water, although there are a few saltwater forms. Some species live in damp soil or on the bark of trees.
Tissues Cells in the body of the multicellular organism are arranged in structural and functional groups called tissues. A tissue is a group of similar cells that work together to perform a particular function. Tissues that are grouped together and work for a common cause form organs. Groups of organs that contribute to a particular set of functions are called systems. The ability of cells to carry out special functions in addition to the usual work of cells exemplifies specialization. When different jobs are accomplished by the various tissues in an organ, we call this division of labor.
Transpiration Loss of water vapor through plant leaves is termed transpiration, a process that is responsible for the rise of sap in trees. Guttation is the loss of liquid water through the leaves of plants with short stems. Guttation is caused by the effect of root pressure on water flow and has hardly any physiological advantage to the plant.
Transport Involves the absorption of materials by living things, including the movement and distribution of materials within the body of the organism. There are several transport methods, including diffusion, active transport, and circulation. Diffusion is the flow of molecules from an area where these molecules are in great concentration to an area where there are fewer of them. Active transport is the movement of molecules powered by energy. Circulation is the movement of fluid and its dissolved materials throughout the body of an organism or within the cytoplasm of a single cell.
Turtles and tortoises The chelonians are the turtles and tortoises. The skeleton is modified to form a box-like covering, the upper curved portion of which is called the carapace, the lower part, the plastron. The head, tail, and legs are the only movable parts of the animal. The jaws are horny and toothless. Chelonians live on land, in freshwater, and in the sea. More turtles live on the American continent than anywhere else.
Twins There are two types of twins: identical and fraternal. Identical twins result from the fertilization of one egg and have the same genetic makeup. They are of the same sex and are almost identical in appearance. They develop in a common chorionic sac and share a common placenta. However, the umbilical cords are separate. Fraternal twins develop from two separate fertilized eggs. They do not share a common genetic makeup and are no more alike than siblings born at separate times. The sexes may be different. Each fraternal twin has its own chorionic membrane and its own placenta.
Umbilical cord The implanted embryo is attached to the uterus by means of the umbilical cord, a structure that contains blood vessels that function in carrying nutrients and oxygen to the embryo and transporting waste away from it. The umbilical cord connects with the placenta, a vascularized organ made up of tissues of the mother and the embryo. The blood of the embryo that circulates in the capillaries of the placenta is separated from the blood of the mother by layers of cells thin enough to allow diffusion between the two circulatory systems. There is no mixing of the blood of the mother with the blood of the embryo. (The term fetus is used in mammalian embryos after the organs have formed.)
Urinary system The human urinary system is located dorsally in the abdomen. This system consists of two kidneys, tubes known as ureters extending from each kidney to a urinary bladder and a single urethra, a tube that leads out of the bladder.
Uterus A muscular sac inside the body of the female mammal specialized for holding the developing young.
Vacuole A space in the cytoplasm enclosed by a membrane and filled with liquid. Some vacuoles are digestive vesicles; some are storage areas. Contractile vacuole is an organelle that pumps excess water out of freshwater protozoans such as the Paramecium.
Vascular plants The vascular plants are truly land-dwelling plants. They have developed adaptations that permit them to live on land independent of bodies of water. The word "vascular" means that these plants have a water-carrying system. Water is conducted upward from the roots by xylem tubules. Fluid compounds are conducted downward from the leaves to lower plant organs by the phloem tubules.
Vegetative propagation In some cases, flowering plants can reproduce more of their kind without the use of flowers, but from stems, leaves, or roots. Since these are the vegetative parts of the plant normally used for nutrition, this method of reproduction is known as vegetative propagation. It is a form of asexual reproduction, since it involves only one parent.
Values of vegetative propagation:
1. The plants are of the same type as the parents. They do not vary, as might usually be the case in sexual reproduction, where the characteristics of two parents are inherited.
2. Plants are reproduced much more quickly and in larger numbers, than if they were grown from seeds.
3. Seedless fruits such as oranges and grapes can be maintained and propagated.
Venereal diseases (VD) Largely spread through sexual intercourse between people who are infected with the germs that cause the diseases. The infection of two such diseases, syphilis and gonorrhea, generally takes place through the mucous membranes of the reproductive organs or the mouth. A pregnant woman who has one of these diseases may give birth to a deformed or dead baby. Blindness may also affect the newborn. As a precaution, it is common practice in hospitals to treat the eyes of newborn babies with silver nitrate.
Vertebrates Animals that have a true backbone composed of segmented parts called vertebrae belong to the chordate subphylum Vertebrata. The vertebrae may be made of cartilage or bone: if made of the latter, cartilage cushions prevent the bones from rubbing together. The backbone is built around the notochord and usually obliterates it. Vertebrates vary in size from large to small, but all have a living endoskeleton usually made of bone. All vertebrate species have marked development of the head where a brain is enclosed in a cranium. Blood is pumped through a closed circulatory system by means of a ventral heart, having at least two chambers: an atrium and a ventricle. The hepatic portal system carries blood laden with food from the intestines to the liver before it reaches the body cells. Vertebrate red blood cells contain the iron-bearing pigment hemoglobin that is specialized to carry oxygen. Such a system of closed blood vessels prevents blood from entering the body cavity. Most vertebrates (except humans) have a post-anal tail that is a continuation of the vertebral column. Although there are never more than two sets of paired appendages, some adult vertebrates show only one such set or none at all, the appendages having been lost over evolutionary time. Evidence of lost appendages may be seen in embryonic forms or may be demonstrated by vestigial structures. The coccyx bone in humans is a remnant (vestigial structure) of a post-anal tail. Other characteristics of vertebrates include a mouth that is closed by a movable lower jaw and a thyroid gland derived from the ventral wall of the pharynx. In the invertebrate chordates, the endostyle is an evolutionary signpost pointing to the development of the thyroid gland.
Viruses Viruses are not living. They are not cells and they do not exhibit the characteristics of life as do cells. Viruses can reproduce only within living cells. The virus particle is known as a virion. It merely consists of a protein coat and a nucleic acid core. The protein coat, called a capsid, may be shaped like a rod, be polyhedral, or have a tail with extending fibers. In some viruses, including those that cause influenza, a cytoplasmic membrane surrounds the protein coat. This surrounding envelope may come from the plasma membrane of the host cell or may be synthesized by the host's cytoplasm. However, virologists have found that the envelope contains proteins that are virus-specific. Viral nucleic acid may be a single molecule consisting of as few as five genes or may have as many as several hundred. Viral nucleic acid may be single or it may be double-stranded; it may be circular or linear. Some viral nucleic acid is made of DNA (deoxyribonucleic acid); others have only an RNA (ribonucleic acid) core. Viruses never contain both DNA and RNA. See Bacteriophage.
Vitamins Are organic compounds. They are classified as water soluble or fat soluble. In general, the water soluble vitamins are coenzymes necessary to the proper sequence of biochemical events that occur during cellular respiration. It is interesting to note that the primates (Homo sapiens included) and guinea pigs are the only vertebrate animals that cannot synthesize their own vitamin C from carbohydrates. Therefore, the daily requirements of ascorbic acid must be met through food intake. The functions of the fat soluble vitamins are not clearly understood. For detailed information on vitamins, See Health and Medicine.
Water, conservation of Water is rendered useless for drinking, bathing, irrigation, and as a habitat for fish when polluted by the chemical wastes from industry and by human sewage. Sewage treatment plants clean up sewage before it is dumped into waterways. Special treatment must be given to chemical wastes to detoxify them before disposal. Water is a renewable resource. However, people on the earth are using more water than ever before in industry, refrigeration, agriculture, and the like. Humans are dependent on rainfall to maintain an adequate water table (level of groundwater) and to replenish water stores in reservoirs. The wasting of water through careless use can have serious consequences for human life.
Water cycle There are three ways in which water vapor enters the atmosphere. Water evaporates from land surfaces and from the surfaces of all bodies of water. Water vapor enters the air as a waste product of respiration of animals and plants. For example: every time you exhale, water vapor is released into the air. Great amounts of water are lost from plants through the openings in the leaves; this water loss due to evaporation is called transpiration. Water vapor in the air is carried to high altitudes where it is cooled and forms clouds by condensation. Eventually, clouds fall to the earth in the form of precipitation: rain, snow, or sleet. Most of the precipitation returns to the oceans, lakes, or stream and less than 1 percent of it falls on land. Of the water that does fall on land, about 25 percent of it will evaporate from the various land surfaces before it can be absorbed by plants or used by animals. Water that does not evaporate enters the soil and becomes available to plant roots and soil organisms. Soil water that is not absorbed by plants seeps down into the ground until it reaches an impervious layer of rock. The water moves along this rock as groundwater until it reaches an outlet into a larger body of water such as a lake or an ocean. The water cycle repeats.
White blood cells (Leucocytes) There are five types of white blood cells, functioning to protect the body against invading foreign proteins. The amoeboid-like neutrophils and monocytes behave as phagocytes, engulfing bacteria and other foreign proteins. Eosinophils detoxify histamine-like secretions. Lymphocytes participate in immune responses and basophils produce anticoagulants.
Woody stems Stems have three major functions. First, they conduct water upward from the roots to the leaves and conduct dissolved food materials downward from the leaves to the roots. Second, stems produce and support leaves and flowers. Third, they provide the mechanisms for the storage of food. Woody stems are composed of primary and secondary tissues. Primary tissues are those that develop from the meristems (embryonic tissue) of the buds on twigs during the first year of growth. After the first year, growth in the woody stem takes place in the secondary tissues. These are tissues that arise from the cambium.
Worm-Parasites Diseases Caused by Diseases Caused by Flatworms Roundworms Tapeworm Infection Hookworm Sheep Liver Fluke Trichinosis Infection Ascaris Infection Chinese Liver Fluke Pinworm Infection Infection Filariasis
Xylem Water-carrying (vascular) tissue in plants that conducts water from the roots upward.
Zoospores Free-swimming cells with flagella that are produced by asexual cell division of the green algae Chlamydomonas. The zoospores mature, develop a large chloroplast, and become vegetative Chlamydomonas cells.
Zygote Fertilized egg formed by the union of egg and sperm. The zygote has the 2N chromosome number. Following zygote formation, the cell goes into a series of divisions known as cleavage.
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