This collection of Pages has been organized by Susan Harrell and Monica Beals under the supervision of Louis Gross at the University of Tennessee, Knoxville, with support from the National Science Foundation Undergraduate Course and Curriculum Program through Award DUE-9752339, "Alternative Routes to Quantitative Literacy for the Life Sciences".

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A

acid - a substance that dissociates to form H+ ions when dissolved in water; has a pH less than 7.

actin - one of two proteins that make up myofilaments; provides cell with mechanical support and plays roles in cell shape and movement.

adaptation - a feature or trait that confers some selective advantage on individuals possessing it, and has therefore become predominant in the population.

allele - one of multiple forms of a gene; different alleles often have different phenotypic effects.

allometry - the measurement or study of of the changing proportions of the parts of an organism as its overall size changes; "allometric growth" refers to differing growth rates of different features of an organism during development.

allozyme - one of multiple forms of an enzyme, each coded for by a different allele at a given locus.

alveoli - one of many small, thin-walled air sacs within the lungs.

amino acids - molecules containing an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a functional group designated R, all bonded to a central carbon atom; the building blocks of proteins.

antibody - a protein substance produced in the blood in response to foreign substances that marks them for destruction by other elements of the immune system.

antigen - a foreign substance in the bloodstream that stimulates the production of antibodies.

arteriole - a small artery, leading from arteries to capillaries.

artery - a tubular branching vessel of the circulatory system that carries blood away from the heart to the tissues.

ATP - adenosine triphosphate; composed of ribose, adenine, and a triphosphate group; the chief energy currency of cells.

auxin - a plant hormone that controls elongation and other effects.
 

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B

base - a substance that combines with H+ ions; has a pH greater than 7.
 

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C

Calvin-Benson Cycle - the series of dark reactions in which ATP and NADPH produced by the light reactions are used to fix carbon.

capillary - a very slender blood vessel joining the ends of arteries and the beginnings of veins.

carbohydrates - an organic compound consisting of a chain or ring of carbon atoms to which hydrogen and oxygen atoms are attached in a ratio of approximately 1:2:1.

carrying capacity - the maximum population size that can be supported in an environment; reflects the availability of resources in the environment.

cell cycle - the five phase process by which a eukaryotic cell divides into two daughter cells.

cell membrane - the phospholipid and protein layer that encases living cells.

chemoreception - the process of detecting chemicals in the environment.

chromosomes - in a eukaryotic cell, long threads of DNA associated with a protein which contain hereditary information.

circadian rhythm - endogenous rhythms of about 24 hours that occur even in the absence of external cues.

codons - the basic unit of the genetic code; a sequence of 3 nucleotides in DNA or mRNA that code for one amino acid or polypeptide termination.

competitive exclusion - the extinction of a population from an area or community as a result of competition with another species.

concentration - the number of molecules per unit volume.

cytoplasm - a semifluid matrix that occupies the volume between the nucleus and cell membrane.

cytoskeleton - in eukaryotic cells, a network of protein fibers that support the shape of the cell and anchor organelles.
 

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D

dendrite - a branched process extending from a neuron that conducts impulses toward the cell body.

density dependence - the tendency of population dynamics to be affected by the density of the population.

diffusion - the random movement of molecules that tends to distribute molecules uniformly, from regions of higher to lower concentration.

diploid - a cell or organism that has two gene copies at each locus (i.e., two sets of homologous chromosomes) (compare with haploid)

DNA - deoxyribonucleic acid; the basic storage vehicle of hereditary information, stored as a sequence of nucleotides in two winding polymer strands (the double helix).
 

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E

embryo - the early developmental stage of an organism produced from a fertilized egg.

endergonic reaction - one in which the products contain more energy than the reactants; requires an input of energy in order to proceed.

enzyme - a protein capable of speeding up a chemical reaction by lowering the energy required to activate the reaction, but remains unchanged during the process.

equilibrium point - a point to which a system tends to return following some perturbation; a given system may have multiple equilibrium points.

exergonic reaction - one in which the reactants contain more energy than the products; tends to proceed spontaneously.
 

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F

facilitated diffusion - the transport of molecules across a membrane via a carrier protein in the direction of lower concentration.

fatty acids - a long hydrocarbon chain ending with a -COOH group; components of fats, oils, phospholipids, and waxes.

fecundity - the number of gametes or offspring produced by an individual (usually calculated for females).

fixation - when the frequency of an allele in a population becomes 1 (i.e., no other alleles are present).

flagella - fine, long threadlike organelles protruding from the surface of a cell that are capable of rotary motion that propels cells.
 

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G

gene flow - the exchange of genes between populations resulting from migration of individuals or dispersal of gametes.

genetic drift - changes in allele frequencies within a population due to random processes (i.e., not selection); most prevalent in small populations.

genotype - the genetic make-up of an organism (compare with phenotype).

giberellins - plant hormones that are produced in the apical regions of shoots and roots and play a major role in controlling stem elongation.

Gibb's free energy - excess, usable energy released by exergonic reactions.

glycolysis - the harvesting of chemical energy by rearranging the chemical bonds of glucose to form two molecules of pyruvate and two molecules of ATP.

gravitropism - the response of a plant to gravity, which generally causes shoots to grow up and roots to grow down.

growth factor - a protein substance or hormone that signals cells to divide.
 

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H

haploid - a cell or organism that has a single gene copy at each locus (compare with diploid).

hemoglobin - a globular protein in vertebrate red blood cells and in the plasma of many invertebrates, that carries oxygen and carbon dioxide.

heterozygosity - the average proportion of loci at which an individual in a population is heterozygous.

heterozygous - possessing different alleles at corresponding loci on different chromosomes.

homeotherm - an organism that maintains a more-or-less constant body temperature ("warm-blooded"); as opposed to an ectotherm, whose body temperature is determined by an external heat source.

homozygous - possessing the same alleles at corresponding loci on different chromosomes.
 

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I

isocline - a line on a graph connecting points at which a population's growth rate does not change; the points can represent combinations of resource abundances or species densities.  A zero isocline connects points on the graph at which the population's growth rate is zero.
 

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L

locus (pl. loci) - a location on a chromosome occupied by a given gene.
 

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M

mesophyll cells - the non-vascular tissue of a leaf, found between the upper and lower epidermis; the primary tissue in which chloroplasts are found and thus in which photosynthesis occurs.

metabolism - the process by which all living things assimilate energy and use it to grow.

microtubules - in eukaryotic cells, long hollow cylinders composed of the protein tubulin; they influence cell shape, move chromosomes during cell division, and provide internal structure of cilia and flagella.

mitochondria - sausage-shaped organelles bound by two membranes that carry out the cell's oxidative metabolism.

mitosis - the process of cell division that produces two daughter cells with the same genetic composition of the parent cell; in multicellular eukaryotes this results in somatic (body) growth; in single-celled eukaryotes it results in reproduction.

mRNA - messenger ribonucleic acid; assembled from chromosomes in the nucleus then passes to ribosomes in the cytoplasm to synthesize polypeptides.

myofibrils - a contractile microfilament within muscle, composed of actin and myosin.

myosin - one of two protein components of myofilaments.
 

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N

neuron - a nerve cell specialized for signal transmission.

nucleoplasm - a semifluid matrix which occupies the volume within the nucleus.

nucleotide - a single unit of nucleic acid, composed of a phosphate, a five-carbon sugar, and a purine or pyrimidine.

nucleus - a spherical organelle characteristic of eukaryotic cells that contains the genetic information of a living cell.
 

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O

organelle - a specialized structure within a cell.

osmoregulation - the maintenance of a constant internal solute concentration by an organism, regardless of the external environment.

osmosis - the diffusion of water across a membrane that permits the free passage of water but not that of one or more solutes.

osmotic pressure - the increase of hydrostatic water pressure within a cell as a result of water molecules that continue to diffuse inward toward the area of lower water concentration.
 

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P

permeability - the ability of molecules to pass through the cell membrane.

phenotype - the expression of an organism's genotype in terms of morphology, physiology, behavior, etc., determined by the interaction between genotype and environment.

phloem - in vascular plants, a food-conducting tissue composed of sieve elements and various other kinds of cells and fibers.

photophosphorylation - a fundamental form of photosynthetic light reaction in which organisms use a network of chlorophyll molecules to channel photon energy to the electron transport chain.

photorespiration - a process in which CO2 is released without the production of ATP or NADPH; acts to undo the work of photosynthesis.

photosynthesis - the process by which plants, algae, and some bacteria use the energy of sunlight to create more complicated molecules from carbon dioxide and water.

phototropism - a growth response of a plant to a uni-directional source of light.

platelets - a fragment that floats in the blood and plays a role in controlling blood clotting.

product - substrates produced by a chemical reaction.

proteins - a long chain of amino acids linked end to end by peptide bonds.
 

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R

reactant - substrates that undergo a chemical reaction in order to form products.

red blood cell - oxygen-carrying cells in the bloodstream, packed with hemoglobin.

regression - in statistics, an analysis of the mathematical relationship(s) between a response variable and one or more predictor variables.

replication - the process by which genetic information in the form of DNA is duplicated during cell division.

respiration - in cells, the oxidation of food molecules to obtain energy; in terrestrial vertebrates, the inhalation of oxygen and exhalation of carbon dioxide.
 

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S

sarcomere - the repeating bands of actin and myosin that make the fundamental unit of contraction in skeletal muscle.

sieve tubes - a series of cells arranged end-to-end and connected by plates in the phloem of angiosperms.

sigmoidal - "s"-shaped (as in a logistic growth model, where the growth rate increases rapidly initially but reaches a point after which the rate of increase in growth rate occurs progressively more slowly).

sperm - the human male gamete.

stomata - specialized openings in the leaves of some plants that allow carbon dioxide to pass into the plant body and water and oxygen to pass out.

substrate -a molecule on which an enzyme acts.
 

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T

taxon (pl. taxa) - a group of organisms belonging to the same category or group (i.e., a species, family, order, or other classification grouping).

trachea - a long tube connecting the mouth to the bronchial tubes connected to the lungs.

transcription - the phase of gene expression in which a polymerase enzyme assembles an mRNA molecule from a complementary DNA molecule.

turgor pressure - pressure within a cell resulting from the movement of water into the cell.
 

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V

vein - a blood vessel carrying blood from tissues to the heart.

venule - a small vein, typically beginning in the capillaries and conneting to larger veins.
 

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X

xylem - in vascular plants, a tissue that conducts water from the roots throughout the plant and provides structural support; consists of parenchyma cells, tracheids, vessels, and woody fibers.

Sources

Begon, M., J. L. Harper, and C. R. Townsend.  1996.  Ecology:
Individuals, Populations, and Communities, 3rd ed.
Blackwell Science Ltd., Cambridge, MA.

Campbell, N. A.  1996.  Biology, 4th ed.
Benjamin/Cummings Publishing Co., Inc., Menlo Park, CA.

Futuyma, D. J.  1998.  Evolutionary Biology, 3rd ed.
Sinauer Associates, Inc., Sunderland, MA.

Gotelli, N. J.  1998.  A Primer of Ecology, 2nd ed.
Sinauer Associates, Inc., Sunderland, MA.

Hartl, D. L., D. Freifelder, and L. A. Snyder.  1988.  Basic Genetics.
Jones & Bartlett Publishers, Inc., Portola Valley, CA.

Raven, P. H. and G. B. Johnson. 1991. Understanding Biology.
Mosby, Inc., St. Louis, MO.
 

Copyright 1999 M. Beals, L. Gross, S. Harrell