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Glossary of Biological Terms


abdomen, Posterior section of the body; between diaphragm and pelvis in vertebrates.

absorption, The passage of liquids through a cell membrane.

adaptation, Fitness of structure for function; fitness for environmental conditions.

ADP, adenine diphosphate, A low-energy compound produced during respiration.

adrenal, Ductless glands above the kidneys; “glands of combat.”

Adrenalin, Laboratory product that has the chemical make-up of adrenin.

adrenin, A hormone secreted by the inner part of the adrenal glands.

adventitious, Appearing in an unusual place (roots above ground).

afferent, Nerves that receive stimuli and send impulses to the brain or spinal cord.

agar agar, Gelatin material obtained from seaweed; used in bacteriology.

algae, Simplest green plants.

alternation of generations, Life cycle in which an asexual generation follows a sexual generation.

altricial, Born helpless.

ameba, Simplest (one-celled) animal.

amphibian, Vertebrates that live part of their lives in water and may live part of their lives on land.

anal spot, Weak point in cell membrane for elimination of solid wastes (paramecium).

anemia, Deficiency of red blood corpuscles or hemoglobin in red blood corpuscles.

antennae (sing.: antenna), Sense organs, or “feelers,” on heads of insects and related arthropods.

anther, Pollen-producing structure of the stamen of flowering plants (part of male reproductive organ).

anthropologist, One who specializes in the study or science of man and his activities as a rational animal.

antibiotic, Chemical substance produced by a living thing which can stop growth of some disease-producing bacteria, virus, or protozoa.

antibodies, Chemical substances in blood that fight against bacteria, toxins and other foreign substances.

antiseptic, A substance that prevents growth of some bacteria and destroys others.

antitoxin, A substance produced in animal bodies that counteracts harmful effects of disease-producing organisms; may provide immunity to certain diseases.

aphid, “Ant-cow”; provides nourishing fluid for ants; receives shelter and protection from ants.

appendage, A structure or organ attached to the main body.

appendix, Vestigial organ in man; part of digestive tube.

aquatic, Water-living.

arboreal, Tree-living.

Archaeopteryx, Fossil bird-form showing relationship to reptiles.

arteriosclerosis, Hardening of the arteries.

artery, Blood vessel that carries blood away from the heart to all parts of the body.

aseptic, Free of microorganisms; sterile.

asexual, Reproduction without the union of two unlike parent cells.

assimilation, Process by which digested food is changed into protoplasm.

astigmatism, Defect in the curvature of the eyes; results in indistinct vision.

atabrine, Synthetic drug used in the treatment of malaria.

atoll, Coral reef in the form of a ring.

atom, The smallest quantity of an element that enters into chemical combination.

ATP, adenine triphosphate, A high-energy compound produced during respiration.

auricle, Upper chamber of the heart which receives blood from the veins.

Australopithecus africanus, A South African man-ape genus, a meat-eater and tool-user, a member of the Australopithecine group.

Australopithecines, A group of man-apes, ancestral to man, who lived around 3 million years ago.

auxin, Plant hormone that controls plant growth.

axon, Main, long fiber or branch leading from a neuron; carries impulses away from neuron cell body.


bacillus, Rod-shaped bacteria.

backbone, Bony, internal vertebral or spinal column.

bêche-de-mer, Sea cucumbers, dried and used for food (related to starfish).

beriberi, Deficiency disease caused by lack of thiamin (B1 of B complex).

binary fission, Simple splitting of a parent cell into two daughter cells.

bivalve, Mollusk having two shells (clam, oyster).

botulism, Food poisoning caused by specific bacteria.

bronchi, Bronchial tubes branching from the trachea or windpipe and leading into each lung.

budding, Form of asexual reproduction; growth from mother cell which remains attached to or separates from mother cell.


calcareous, Made of calcium.

calorie, A heat-measuring unit used in reference to foods.

calyx, Sum total of sepals or outermost leaflike structures of a true flower.

capillary, Smallest blood vessel in the body; between and connecting an artery and a vein; in closest contact with body cells for exchange of digested food, gases, and waste fluids.

carnivorous, Meat-eating.

cartilage, Soft, flexible, prebone tissue; “gristle.”

castings, Undigested solids containing soil (excreted from the earthworm); enriches the topsoil.

catalyst, Activating agents that bring about changes but are not themselves changed during the processes.

caterpillar, Larval stage in the metamorphosis of butterfly and moth.

cattaloes, Hybrids resulting from cross-breeding of a buffalo and a cow.

cell, The unit of protoplasmic structure and function of all living things.

cellulose, Organic substance found in the cell walls of plant cells.

cerebellum, Part of the vertebrate brain behind the cerebrum; regulates muscular activity and controls body balance.

cerebrum, Largest area of brain; center of conscious mental processes and voluntary muscular activity.

chemotherapy, Branch of medical science; study of the use of drugs and other substances of chemical nature in the treatment of specific diseases.

chlorophyll, Green color pigment in plant cells; necessary for photosynthesis.

choroid coat, Membrane around the eyeball that contains blood vessels for nourishment and pigmentation for eye color.

chrysalis, Pupa stage of butterfly (similar to cocoon of moth); quiescent stage before adulthood.

cilia, Threads of protoplasm surrounding entire cell of paramecium; used for locomotion.

coccus, Round type of bacteria.

coccyx, Bone at end of spinal column consisting of four fused vertebrae; tail-like vestigial structure in man.

cochlea, Snail shell-like portion of inner ear which contains nerve endings of auditory nerve.

cocoon, Pupa stage in the metamorphosis of a moth; quiescent stage.

colchicine, Plant extract (drug type) used in experiments on Jimson weeds to induce formation of mutants.

cold-blooded, Having the same body temperature as that of the immediate environment.

compound, A substance resulting from the chemical combination of one or more elements.

conditioned reflex, An acquired response; a response to a stimulus other than the usual or original one.

conjugation, Temporary union of two similar cells during which there is an exchange of nuclear material.

corm, An underground plant stem that stores food for the plant.

cornea, Transparent layer covering the front of the eyeball.

corolla, The sum total of the petals of a flower.

corpuscle, Blood cell (red or white).

cotyledon, Part of a seed that contains stored food for the embryo plant.

cretin, One who was born with a serious deficiency of the thyroid gland.

cutin, Transparent, waxy secretion that protects outer surface of some leaves.

cytoplasm, Protoplasm of the cell minus the nucleus.


dendrite, A branching process of a neuron which carries impulses to the cell body.

dental caries, Tooth decay.

dentine, Bony portion of the tooth beneath the enamel.

diaphragm, A layer of muscle tissue that separates the chest from the abdominal cavity in mammals; important in breathing process.

diatom, A species of algae; cell is enclosed in boxlike shell containing silica.

diffusion, Spreading of molecules of gas or liquid from an area of greatest density toward an area of lower density.

dinosaur, Extinct, prehistoric reptile.

disinfectant, A substance used to destroy harmful bacteria; usually too strong to be used on the body.

dissemination, Distribution (as of seeds).

dominant, Referring to hereditary characteristics or traits that show in a hybrid.

DNA, Deoxyribonucleic acid, The material in a cell that makes up the genes and controls the cell.


ecology, The study of the relationships of living things to one another and to their environment.

ectoderm, The outer layer of cells; one of the three germ layers of an embryo.

efferent, Referring to nerves that carry impulses away from the brain to glands or muscles; motor nerves.

electrocardiograph, A machine used to make a recording of electrical waves from the heart; used in diagnosis of heart conditions.

element, A substance that cannot be further simplified by chemical means.

embryo, A young plant or animal before germination or birth.

endocrine, Referring to ductless glands that secrete hormones or “body regulators.”

endoderm, The inner layer of cells; an embryonic layer.

endoplasmic reticulum, The cell “skeletal system”; provides transport system between cell parts and a surface on which reactions may take place.

endoskeleton, Bony skeleton within the body of vertebrate animals.

enzymes, Chemical substances in plants and animals that induce or hasten chemical changes (as in digestion) without being, in themselves, changed.

Eohippus, Prehistoric horse.

epiglottis, A lid of tissue that covers the opening of the windpipe or trachea during the act of swallowing.

erosion, The wearing away of a substance (soil) by the action of water, wind, etc.

esophagus, The gullet, or food tube, leading from the mouth to the stomach.

estrogen, Female hormone, responsible for secondary sex characteristics.

eugenics, The study of the improvement of the human race, applying the laws of heredity.

euthenics, A science that deals with improving the race by improving the environment.

evolution, Succession of gradual changes that take place in an individual plant or animal or species of plant or animal or form of life, over a long period of time, usually from the simple toward the more complex.

excretion, The process by which waste products are eliminated from a living organism.

exoskeleton, An outer or external skeleton (shell of crayfish).


fauna, Animals within a given life zone or natural habitat.

feces, Indigestible, solid waste materials.

fertilized egg, Result of the union of male cell with female cell.

fetus, Unborn young of mammals, after it has assumed the appearance of the parents.

fibrinogen, A substance in the blood plasma that is changed to fibers to form a “clot” under certain conditions.

fins, Organs of locomotion, steering, and balance of fish.

flaccid, A soft or relaxed condition of a cell, usually due to lack of water within the cell.

flora, Sum total of all plants within a given life zone or natural habitat.

fossil, Petrified remains, imprints, tracks, or other markings of prehistoric plants or animals.

fraternal twins, Twins that develop from two separate eggs fertilized at approximately the same time.

frond, The leafy part of a fern.

fruit, A ripened ovary and its contents (seeds) plus any parts of the flower adhering closely to the ovary.

fry, Young fish with yolk sac still attached but almost used up.

function, The use or work of any living organism or part thereof.

fungus, Plant that lacks chlorophyll; a thallophyte (simplest group); dependent on dead or living organic food.


gamete, A sexual reproductive cell; a female gamete is an ovum or egg cell and a male gamete is a sperm cell.

gametogenesis, Process during which gametes, or sex cells, are formed.

ganglion, A mass of nerve cells.

gene, A unit in a chromosome that carries hereditary characteristics.

genetics, The science of heredity.

geologist, One who studies the science of geology, the study of the earth's crust, past and present.

gills, Organs of breathing of fish.

gizzard, Muscular organ of earthworms, birds, and some other animals in which food is crushed and partly digested.

glycogen, “Animal starch”; a carbohydrate stored in the liver and present in muscles.

Golgi bodies, Help to produce secretions in animal cells.

grafting, Joining a twig or scion to another plant stem called a stock.

guard cells, Cells on either side of a stoma which regulate the size of the stoma opening.

gullet, Esophagus or food tube extending from the back of the mouth to the stomach.


hemoglobin, Red coloring matter in red blood corpuscles of vertebrates; an organic compound that carries oxygen.

hemophilia, Hereditary disease in which the blood will not clot normally even after a slight injury.

herbivorous, Plant-eating animal.

heredity, The passing on of traits or characteristics from parent to offspring through the gametes.

hibernate, Prolonged sleeplike inactivity during a winter season (bears, frogs, etc.).

Homo erectus, Recent ancestors of man, who made tools in the Acheulian Tradition.

Homo habilis, An ape-man ancestor, the first to make tools.

Homo sapiens, Scientific name of present-day man.

hormone, Substance that is secreted by ductless or endocrine glands directly into the bloodstream; controls actions in some part of the body or some body process; “chemical messengers.”

humus, Substances in soil formed by decay of plants and animals.

hybrid, A plant or animal carrying unlike genes in the same pair of chromosomes.

hybridization, Crossing individuals in breeding that carry contrasting traits.

hypocotyl, Part of a plant embryo that develops into the root of the plant.


identical twins, Twins that result from the fertilization of a single egg cell which splits into two like parts in early cell division.

immunity, Ability to resist a certain disease because of a previous attack or natural ability to resist it or by pre-ventative inoculations, vaccinations, etc.

incisor, The cutting teeth with chisel-like edges; front teeth in jaws of mammals.

ingestion, Process of taking in food.

inorganic, That which is not alive, nor ever was alive, nor came from anything alive.

insectivorous, Insect-eating animal or plant.

insulin, A hormone secreted by the islands of Langerhans of the pancreas; controls oxidation of sugars.

invertebrate, An animal without a backbone.

iris, The colored part of the eye of vertebrate animals.

irradiation, Exposure of food, human skin, etc. to ultraviolet rays.


kelp, Brown algae seaweed; used for food in China and Japan; burned to produce iodine.

kidney, Paired organs in vertebrates that extract nitrogenous wastes from the blood for elimination.


Lacteal, Small lymph vessel in the center of each villus; absorbs digested fats from the small intestines.

larva, Wormlike, eating stage in the complete metamorphosis of some insects (caterpillar of moth and butterfly, maggot of fly).

larynx, Voice box (“Adam's apple”) in the trachea; contains vocal cords.

lateral line, Line of nerve cells on sides of fish; indicates depth of water for the fish; helps keep balance.

legume, Plants that have pod fruits (peas, beans).

lens, A transparent body in the eye that is biconvex; light rays pass through the lens and are bent to focus on the retina.

lichen, A symbiotic relationship between a fungus plant and a green algae; common on moist rock surfaces.

ligament, A band of tissue that connects bone to bone.

linkage, Referring to the grouping together of genes (in a chromosome) that are transmitted together to the offspring.

lungs, Organs of breathing of vertebrate animals from adult amphibians through mammals.

lymph, Part of the blood serum which is outside the blood vessels; bathes the cells.

lysosomes, Contain digestive enzymes in animal cells.


maggot, Larval stage in the metamorphosis of the common housefly.

malaria, Disease caused by a parasitic protozoan (malarial plasmodium) which is carried by and transmitted by the anopheles mosquito; plasmodium lives in the bloodstream of man (alternate host).

mammals, Vertebrates that have hair on their bodies, breathe by means of lungs, bear their young alive, and nourish their young with milk from mammary glands.

mammary gland, Milk-secreting glands of mammals.

medulla oblongata, Posterior part of the brain connecting the spinal cord; controls respiration and heartbeat.

meiosis, Reduction division; reduction of original number of chromosomes so that each sex cell (egg or sperm) has half the original number of chromosomes characteristic of the species.

mesentery, Tissue that holds the intestine in place in the abdominal cavity.

mesoderm, The middle layer of cells formed during embryonic development.

metamorphosis, The changes in form an organism undergoes during its development from the egg to the adult stage.

mitochondria, Where food is oxidized and energy produced in a cell for the cell activities.

mitosis, Cell division during which the chromatin material (chromosomes) splits in half making like pairs.

mixture, The physical combination of two or more elements or compounds, each of which retains its original characteristics and can be separated from each other.

molecule, Smallest particle of a compound capable of having the properties of the compound.

morphology, The study of the structure of plants and animals.

mutation, A sudden appearance of a new trait or variation that is heritable.

myxedema, A disease in adults resulting from a deficiency of thyroid hormone.


nacre, “Mother-of-pearl”; substance that forms a pearl in the “irritated” bivalve.

neuron, A nerve cell.

nitrate, A compound containing nitrogen, oxygen, and at least one other element.

nuclear membrane, Double membrane around the nucleus of a cell that controls movement in and out of the nucleus.

nucleus, Specialized protoplasm in a cell that controls all cellular activity in general and governs heredity in reproduction in particular (contains chromatin material).


oogenesis, Process of sex-cell reproduction in the female.

organ, A group of different tissues working together to perform a specific function.

organic, Pertaining to something living, or which was at one time living, or which was produced by something living.

organism, Any living plant or animal.

osmosis, Diffusion through a semi-permeable membrane.

ovary, Organ of the reproductive system of flowering plants and higher animals in which eggs are produced.

oxidation, The chemical combination of oxygen with another element.


paleontologist, One who studies fossils.

pancreas, A digestive gland that pours digestive juice into the small intestine; also a ductless gland that controls sugar oxidation.

Paranthropus (Australopithecus robustus), Vegetarian member of the Australopithecines.

parasite, An organism that takes its nourishment from another living organism without giving any benefits to its host.

parathyroid, Ductless or endocrine glands near the thyroid glands in the neck; regulates calcium assimilation in the body.

Pasteurization, Process of treating milk by heating it to 145° F. and rapidly cooling it, thereby killing most of the harmful bacteria therein.

pathogenic, Referring to disease-producing bacteria.

pellagra, Deficiency disease resulting from lack of vitamin niacin (PP of B complex).

pelvis, Broad bones that support the organs of the abdomen.

penicillin, An organic chemical product isolated from a common mold; used in treating diseases caused by certain types of bacteria; now synthesized.

pericardium, A membrane surrounding and protecting the heart.

peristalsis, Wavelike muscular motion of the food tube of higher vertebrate animals which forces food along alimentary tube.

phagocyte, White corpuscles of the blood which act as scavengers.

photosynthesis, Manufacture of carbohydrates by the green plant in the sunshine.

pineal, An endocrine or ductless gland located in the brain; active only in early childhood, regulating growth.

pistil, The female reproductive organ in the flowering plant.

pituitary, Ductless or endocrine gland; called the “master gland” because it controls all other endocrine glands.

plankton, Minute forms of plant and animal life floating near the surface in the ocean.

plasma, The liquid portion of the blood of vertebrates.

platelets, Small cells in blood that aid in clotting.

Pleistocene, Period of earth from 1,750,000 years ago to 50,000 years ago.

pleurococcus, Single-celled (algae) green plant that grows on the shady side of tree trunks; the “Indian's Friend.”

plumule, Part of the plant embryo that develops into the shoot with its leaves.

pollen, Grains formed in the anther of a flower or the male cone of an evergreen; contains sperm, or male sex cells.

pollination, Transfer of pollen from the anther of a flower to the stigma.

precocial, Young born relatively independent of their parents.

primate, Order of mammals that includes monkeys, apes, etc., and man.

Proconsul (Dryopithecus africanus), Prehistoric ape.

protein, A food nutrient necessary for the building of protoplasm; contains nitrogen in addition to oxygen, hydrogen, and carbon.

protoplasm, The living substance of all plants and animals.

pseudopod, Projection of protoplasm; aids in locomotion of ameba.

ptomaine, A type of food poisoning produced by bacteria of decay.

pulp, Innermost section of a human tooth; contains blood vessels and nerves.

pulse, Rhythmic wave of motion indicating beat of the heart felt in an artery.

pupa, Quiescent stage in the complete metamorphosis of an insect; stage during which the adult develops.

pupil, Referring to the round opening in the iris of the eye through which light rays enter the eye.


quinine, Drug used in the treatment of malaria.


Ramapithecus, Man-ape predecessor of man.

recessive, Referring to a hidden trait or characteristic in a hybrid contrasting pair.

rectum, Terminal end of large intestine; functions in the elimination of solid wastes from the body.

reduction division, See Meiosis.

reflex, Simple, involuntary action in response to a stimulus; no thought involved.

regeneration, The act of growing a new body part for one that has been injured or lost.

reproduction, The process by which new individuals of the same kind are produced by a plant or animal; producing offspring.

respiration, A life function in which oxygen is taken into the cells and the waste gas, carbon dioxide, is given off.

retina, Innermost layer of tissue in the eyeball; contains nerve endings (from optic nerve) that receive light stimulus.

rhizome, Underground plant stem that stores food for the plant.

ribosome, Small body in a cell, the sites of protein synthesis.

rickets, Deficiency disease resulting from an insufficiency of vitamin D in the diet or inadequate assimilation of it.

RNA, ribonucleic acid, Messenger RNA carries genetic code from nucleus to cytoplasm; transfer RNA moves about the cytoplasm picking up amino acids.

roe, Fish eggs.

root hairs, Elongated epidermal cells of a root; for absorption of soil water.


saliva, Digestive juice secreted by glands in the mouth.

saprophyte, Plant or animal that lives on dead organic matter (some fungi).

sclerotic coat, Tough, outer protective layer of the eye.

scurvy, Deficiency disease caused by lack of vitamin C in the diet.

scutes, Scales on the under or belly surface of snakes; aid in locomotion.

secretion, A chemical substance produced by a living cell (enzyme or hormone).

sedimentary, Referring to a type of rock that is formed by materials deposited from suspension in water.

semicircular canal, Part of the inner ear; functions as organ of balance.

Sequoia, Oldest living tree on earth; a giant redwood tree in the evergreen group.

serum, Blood plasma from which the fibrinogen has been removed.

sex-linked, Refers to a hereditary trait whose gene is in the X chromosome.

sexual, Referring to reproduction in which the new individual is a result of the union of an egg cell (female) and a sperm cell (male).

soluble, That which can be dissolved in a fluid.

spawn, To deposit eggs or roe (as fishes).

specialization, Referring to the adaptation of cells or groups of cells to perform a particular function.

sperm, The male sex cell or gamete.

spermatogenesis, Process of sex-cell production in males.

sphygmomanometer, Instrument used to measure blood pressure.

spinal cord, The main nerve cord of all vertebrates.

spiracles, Openings in the abdomen of insects through which they breathe.

spirillum, A spiral-shaped bacterium.

spirogyra, A filamentous green alga; commonly known as “pond scum.”

spleen, Gland in vertebrates (except fish) that destroys used-up red blood cells; a “graveyard” of blood cells.

spore, Nonsexual reproductive body, common to fungi, bacteria, mosses, and other plants and some protozoa.

stamen, Male reproductive organ in flowering plants.

stethoscope, Instrument used to listen to heart sounds and lung sounds.

stigma, Top of a pistil of a flower, part that receives pollen.

stoma, Opening on lower surface of a green leaf through which there is an exchange of gases and water vapor.

streptomycin, An antibiotic used in the treatment and control of tuberculosis and other pulmonary diseases, infections of the urinary tract and other diseases.

symbiosis, A state in which two dissimilar organisms live together to mutual advantage (lichen).

synapse, The space over which a nerve impulse passes from the dendrites of one neuron to the dendrites of another.

system, A group of organs working together to perform a particular function (digestive system).


tadpole, The fishlike stage in the metamorphosis of a frog and a toad.

taxonomist, One who specializes in classification of plants and animals.

tendon, Tissue that attaches a muscle to a bone.

tentacles, Flexible armlike projections of jellyfish and related animals; used in food-getting and locomotion.

testes, The primary male sex organs.

testosterone, Male hormone responsible for secondary sex characteristics.

thorax, The middle division of an animal's body; between the head and abdomen.

thymus, An endocrine or ductless gland; controls growth.

thyroid, An endocrine or ductless gland in the neck, just below the larynx; controls rate of metabolism in the body.

tissue, A group of similar cells that performs the same function.

toxins, Poisons released by disease-producing bacteria.

trachea, Windpipe; tube that delivers air from throat to lungs in vertebrates; air passages in insects.

transpiration, Loss of water by evaporation through the stomates of the leaves of plants.

trichocysts, Dartlike substances ejected by paramecium as a means of defense.

tropism, Response of plants and simple animals to external stimuli.


urea, Nitrogenous waste collected and excreted by the kidneys.

univalve, Mollusk with a single shell (snail).


vaccine, Substance used in preventive inoculation; (virus of cowpox used in inoculation against smallpox).

vacuoles, Small spaces in cytoplasm of a cell, containing liquid or solid food or waste matter.

vein, Blood vessel in which blood returns to the heart from all over the body; liquid-conducting vessels in leaves.

venom, Poison secreted by glands of poisonous snakes, lizards, etc.

ventricle, Lower, muscular chamber of a vertebrate heart; pumps blood through arteries to the rest of the body.

vertebrae, Bones of the backbone.

vertebrates, Group of animals that has internal backbones.

vestigial, Referring to a remnant of a once useful organ or a structure formerly more complete in function.

villus, A small (microscopic) projection in the lining of the small intestine; organ of absorption of digested food.

virus, Submicroscopic substance that has characteristics both organic and inorganic; causative agent of some diseases.


warm-blooded, Referring to an animal that maintains a constant body temperature.


yolk sac, Stored food material for embryo vertebrate.


zygote, The result of the fusion of two dissimilar gametes.

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