AP Biology Glossary Flashcards
1
Q
5’ Cap
A
A modified form of guanine nucleotide added onto the 5’ end of a pre-mRNA molecule.
2
Q
A site
A
One of a ribosome’s three binding sites for tRNA during translation. The A site holds the tRNA carrying the next amino acid to be added to the polypeptide chain. (A stands for aminoacyl tRNA).
3
Q
ABC Hypothesis
A
A model of flower formation identifying three classes of organ identity genes that direct formation of the four types of floral organs.
4
Q
Abiotic
A
Nonliving; referring to the physical and chemical properties of an environment.
5
Q
Abortion
A
The termination of a pregnancy in progress.
6
Q
Abscisic Acid (ABA)
A
A plant hormone that slows growth, often antagonizing the actions of growth hormones. Two of its many effects are to promote seed dormancy and facilitate drought tolerance.
7
Q
Absorption
A
The third stage of food processing in animals: the uptake of small nutrient molecules by an organism’s body.
8
Q
Absorption Spectrum
A
The range of a pigment’s ability to absorb various wavelengths of light; also a graph of such a range.
9
Q
Abyssal Zone
A
The part of the ocean’s benthic zone between 2000 and 6000 m deep.
10
Q
Acanthodian
A
Any of a group of ancient jawed aquatic vertebrates from the Silurian and Devonian periods.
11
Q
Accessory Fruit
A
A fruit, or assemblage of fruits, in which the fleshy parts are derived largely or entirely from tissues other than the ovary. (Examples: strawberry, apple)
12
Q
Acclimatization
A
Physiological adjustment ot a change in an environmental factor.
13
Q
Acetyl-CoA
A
Acetyl coenzyme A; the entry compound for the citric acid cycle in cellular respiration, formed from a fragment of pyruvate attached to a coenzyme.
14
Q
Acetylcholine
A
One of the most common neurotransmitters; functions by binding to receptors and altering the permeability of the postsynaptic membrane to specific ions, either depolarizing or hyperpolarizing the membrane.
15
Q
Acid
A
A substance that increase the hydrogen ion concentration of a solution.
16
Q
Acid precipitation
A
Rain, snow, or fog that is more acidic than pH 5.2.
17
Q
Acoelomate
A
A solid-bodied animal lacking a cavity between the gut and outer body wall. (Ex. Platyhelminthes, Rhynchocoela )
18
Q
Acrosomal Reaction
A
The discharge of hydrolytic enzymes from the acrosome, a vesicle in the tip of a sperm, when the sperm approaches or contacts an egg.
19
Q
Acrosome
A
A vesicle in the tip of a sperm containing hydrolytic enzymes and other proteins that help the sperm reach the egg.
20
Q
Actin
A
A globular protein that links into chains, two of which twist helically about each other, forming microfilaments (actin filaments) in muscle and other kinds of cells.
21
Q
Action potential
A
An electrical signal that propagates (travels) along the membrane of a neuron or other excitable cell as a nongraded (all-or-none) depolarization.
22
Q
Action spectrum
A
A graph that profiles the relative effectiveness of different wavelengths of radiation in driving a particular process.
23
Q
Activation energy
A
The amount of energy that reactants must absorb before a chemical reaction will start; also called free energy of activation.
24
Q
Activator
A
A protein that binds to DNA and stimulates gene transcription. In prokaryotes, activators bind in or near the promotor; in eukaryotes, activators generally bind to control elements in enhancers.
25
Active immunity
Long-lasting immunity conferred by the action of B cells and T cells and the resulting B and T memory cells specific for a pathogen. Active immunity can develop as a result of natural infection or immunization.
26
Active Site
The specific region of an enzyme that binds the substrate and that forms the pocket in which catalysis occurs.
27
Active transport
The movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring an expenditure of energy.
28
Adaptation
Inherited characteristic of an organism that enhances its survival and reproduction in a specific environment.
29
Adaptive immunity
A vertebrate-specific defense that is mediated by B lymphocytes (b-cells) and T lymphocytes (t-cells). It exhibits specificity, memory, and self-nonself recognition. Also called acquired immunity.
30
Adaptive radiation
Period of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different ecological roles in their communities.
31
Addition rule
A rule of probability stating that the probability of any one of two or more mutually exclusive events occurring can be determined by adding their individual probabilities.
32
Adenylyl Cyclase
An enzyme that converts ATP to cyclic AMP in response to an extracellular signal.
33
Adhesion
The clinging of one substance to another, such as water to plant cell walls by means of hydrogen bonds.
34
Adipose tissue
A connective tissue that insulates the body and serves as a fuel reserve; contains fat-storing cells called adipose cells.
35
Adrenal gland
One of two endocrine glands located adjacent to the kidneys in mammals. Endocrine cells in the outer portion (cortex) respond to adrenocorticotropic hormone (ACTH) by secreting steroid hormones that help maintain homeostasis during long-term stress. Neurosecretory cells in the central portion (medulla) secrete epinephrine and norepinephrine in response to nerve signals triggered by short-term stress.
36
Adrenocorticotopic hormone (ACTH)
A tropic hormone that is produced and secreted by the anterior pituitary and that stimulates the production and secretion of steroid hormones by the adrenal cortex.
37
Aerobic respiration
A catabolic pathway for organic molecules, using oxygen (O2) as the final electron acceptor in an electron transport chain and ultimately producing ATP. This is the most efficient catabolic pathway and is carried out in most eukaryotic cells and many prokaryotic organisms.
38
Age structure
The relative number of individuals of each age in population.
39
Aggregate fruit
A fruit derived from a single flower that has more than one carpel. (Example: Raspberry).
40
AIDS
Acquired immunodeficiency syndrome. The symptoms and signs present during the late stages of HIV infection, defined by a specified reduction in the number of T cells and the appearance of characteristic secondary infections.
41
Alcohol Fermentation
Glycolysis followed by the reduction of pyruvate to ethyl alcohol, regenerating NAD+ and releasing carbon dioxide.
42
Aldosterone
A steroid hormone that acts on tubules of the kidney to regulate the transport of sodium ions (Na+) and potassium ions (K+).
43
Algae
A diverse grade of photosynthetic protists, including unicellular and multicellular forms. Algal species are included in three of the five eukaryotes supergroups (Chromalveolata, Rhizaria, and Achaeplastida).
44
Alimentary canal
A complete digestive tract, consisting of a tube running between a mouth and an anus.
45
Allele
Any of the alternative versions of a gene that may produce distinguishable phenotypic effects.
46
Allergen
An antigen that triggers an exaggerated immune response.
47
Allopatric speciation
The formation of new species in populations that are geographically isolated from one another.
48
Allopolyploid
A fertile individual that has more than two chromosome sets as a result of two different species interbreeding and combining their chromosomes.
49
Allosteric regulation
The binding of a regulatory molecule to a protein at one site that affects the function of the protein at a different site.
50
Alpha (α) helix
A coiled region constituting one form of the secondary structure of proteins, arising from a specific pattern of hydrogen bonding between atoms of the polypeptide backbone (not the side chains).
51
Alternation of generations
A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants and some algae.
52
Alternative RNA splicing
A type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns.
53
Altruism
Selflessness; behavior that reduces an individual's fitness while increasing the fitness of another individual.
54
Alveolate
A protist with membrane-bound sacs (alveoli) located just under the plasma membrane.
55
Alveolus
One of the dead-end air sacs where gas exchange occurs in a mammalian lung (plural alveoli).
56
Alzheimer's Disease
An age-related dementia (mental deterioration) characterized by confusion and memory loss.
57
Amacrine cell
A neuron of the retina that helps integrate information before it is sent to the brain.
58
Amino acid
An organic molecules possessing both a carboxyl (-COOH) and an amino (-NH2) group. Amino acids serve as the monomers of polypeptides.
59
Amino group
A chemical group consisting of a nitrogen atom bonded to two hydrogen atoms; can act as a base in solution, accepting a hydrogen ion and acquiring a charge of 1+.
60
Aminoacyl-tRNA synthetase
An enzyme that joins each amino acid to the appropriate tRNA.
61
Ammonia
A small, toxic molecule (NH3) produced by nitrogen fixation or as a metabolic waste product of protein and nucleic acid metabolism.
62
Ammonite
A member of a group of shelled cephalopods that were important marine predators for hundreds of millions of years until their extinction at the end of the Cretaceous period (65.5 mya).
63
Amniocentesis
A technique associated with prenatal diagnosis in which amniotic fluid is obtained by aspiration from a needle inserted into the uterus. The fluid and the fetal cells it contains are analyzed to detect certain genetic and congenital defects in the fetus.
64
Amniote
Member of a clade of tetrapods named for a key derived character, the amniotic egg, which contains specialized membranes, including the fluid-filled amnion, that protects the embryo. Amniotes include mammals as well as birds and other reptiles.
65
Amniotic egg
An egg that contains specialized membranes that function in protection, nourishment, and gas exchange. The amniotic egg was a major evolutionary innovation, allowing embryos to develop on land in a fluid-filled sac, thus reducing the dependence of tetrapods on water for reproduction.
66
Amoeba
A protist grade characterized by the presence of pseudopodia.
67
Amoebocyte
An amoeba-like cell that moves by pseudopodia and is found in most animals. Depending on the species, it may digest and distribute food, dispose of wastes, form skeletal fibers, fight infections, or change into other cell types.
68
Amoebozoan
A protist in a clade that includes many species with lobe- or tube-shaped pseudopodia.
69
Amphibian
Member of the tetrapod class Amphibia, including salamanders, frogs, and caecilians.
70
Amphipathic
Having both a hydrophilic and hydrophobic region.
71
Amplification
The strengthening of stimulus energy during transduction.
72
Amygdala
A structure in the temporal lobe of the vertebrate brain that has a major role in processing emotions.
73
Amylase
An enzyme that hydrolyzes starch (a glucose polymer from plants) and glycogen (a glucose polymer from animals) into smaller polysaccharides and the disaccharide maltose.
74
Anabolic pathway
A metabolic pathway that consumes energy to synthesize a complex molecule from simpler molecules. ("building up", ex. photosynthesis).
75
Anaerobic respiration
A catabolic pathway in which inorganic molecules other than oxygen accept electrons at the "downhill" end of electron transport chains.
76
Analogous
Having characteristics that re similar because of convergent evolution, not homology.
77
Analogy
Similarity between two species that is due to convergent evolution rather than to descent from a common ancestor with the same trait.
78
Anaphase
The fourth stage of mitosis, in which the chromatids of each chromosome have separated and the daughter chromosomes are moving to the poles of the cell.
79
Anatomy
The structure of an organism
80
Anchorage dependence
The requirement that a cell must be attached to a substratum in order to initiate cell division.
81
Androgen
Any steroid hormone, such as testosterone, that stimulates the development and maintenance of the male reproductive system and secondary sex characteristics.
82
Aneuploidy
A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number.
83
Angiosperm
A flowering plant, which forms seeds inside a protective chamber called an ovary.
84
Angiotensin II
A peptide hormone that stimulates constriction of precapillary arterioles and increases reabsorption of NaCl and water by the proximal tubules of the kidney, increasing blood pressure and volume.
85
Anhydrobiosis
A dormant state involve loss of almost all body water.
86
Animal pole
The point at the end of an egg in the hemisphere where the least yolk is concentrated; opposite of vegetal pole.
87
Anion
A negatively charged ion
88
Anterior
Pertaining to the front, or head, of a bilaterally symmetrical animal.
89
Anterior pituitary
A portion of the pituitary that develops from nonneural tissue; consists of endocrine cells that synthesize and secrete several tropic and nontropic hormones.
90
Anther
In an angiosperm, the terminal pollen sac of a stamen, where pollen grains containing sperm-producing male gametophytes form.
91
Antheridium (pl. antheridia)
In plants, the male gametangium, a moist chamber in which games develop.
92
Anthropoid
Member of a primate group made up of the monkeys and the apes (gibbons, orangutans, gorillas, chimpanzees, bonobos, and humans).
93
Antibody
A protein secreted by plasma cells (differentiated B-cells) that binds to a particular antigen; also called immunoglobulin. All antibodies have the same Y-shaped structure and in their monomer form consist of two identical heavy chains and two identical light chains.
94
Anticodon
A nucleotide triplet at one end of a tRNA molecule that base-pairs with a particular complementary codon on an mRNA molecule.
95
Antidiuretic hormone (ADH)
A peptide hormone, also known as vasopressin, that promotes what retention by the kidneys. Produced in the hypothalamus and released from the posterior pituitary, ADH also functions in the brain.
96
Antigen
A substance that elicits an immune response by binding to receptors of B cells, antibodies, or of T-cells.
97
Antigen presentation
The process by which an MHC molecule binds to a fragment of an intracellular protein antigen and carries it to the cell surface, where it is displayed and can be recognized by a T-cell.
98
Antigen Receptor
The general term for a surface protein, located on B-cells and T-cells, that binds to antigens, initiating adaptive immune responses. The antigen receptors on B-cells are called B-cell receptors, and the antigen receptors on T-cells are called T-cell receptors.
99
Antigen-presenting cell
A cell that upon ingesting pathogens or internalizing pathogen proteins generates peptide fragments that are bound by class II MHC (major histocompatibility complex) molecules and subsequently displayed on the cell surface to T-cells. Macrophages, dendritic cells, and B cells are the primary antigen-presenting cells.
100
Antiparallel
Referring to the arrangement of the sugar-phosphate backbones in a DNA double helix (they run in opposite 5' - 3' directions).
101
Aphotic zone
The part of an ocean or lake beneath the photic zone, where light does not penetrate sufficiently for photosynthesis to occur.
102
Apical bud
A bud at the tip of a plant stem; also called a terminal bud.
103
Apical dominance
Tendency for growth to be concentrated at the tip of a plant shoot, because the apical bud partially inhibits axillary bud growth.
104
Apical ectodermal ridge (AER)
A thickened area of ectoderm at the tip of a limb bud that promotes outgrowth of the limb bud.
105
Apical meristem
Embryonic plant tissue in the tips of roots and buds of shoots. The dividing cells of an apical meristem enable the plant to grow in length.
106
Apicomplexan
A protist in a clade that includes many species that parasitize animals. Some apicomplexans cause some human disease.
107
Apomixis
The ability of some plant species to reproduce asexually through seeds without fertilization by a male gamete.
108
Apoplast
Everything external to the plasma membrane of a plant cell, including cell walls, intercellular spaces, and the space within dead structures such as xylem vessels and tracheids.
109
Apoptosis
A type of programmed cell death, which is brought about by activation of enzymes that break down many chemical components in the cell.
110
Aposematic coloration
The bright warning coloration of many animals with effective physical or chemical defenses.
111
Appendix
A small, finger-like extension of the vertebrate cecum; contains a mass of white blood cells that contribute to immunity.
112
Aquaporin
A channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of free water across the membrane.
113
Aqueous solution
A solution in which water is the solvent.
114
Arachnid
A member of a major arthropod group, the chelicerates. Arachnids include spiders, scorpions, ticks, and mites.
115
Arbuscular mycorrhiza
Association of a fungus with a plant root system in which the fungus causes the invagination of the host cells' plasma membranes.
116
Arbuscular mycorrhizal fungus
A symbiotic fungus whose hyphae grow through the cell wall of plant roots and extend into the root cell (enclosed in tubes formed by invagination of the root cell plasma membrane).
117
Archaea
One of two prokaryotic domains, the other being Bacteria.
118
Archaeplastida
One of five supergroups of eukaryotes proposed in a current hypothesis of the evolutionary history of eukaryotes. This monophyletic group, which includes red algae, green algae, and land plants, descended from an ancient protist ancestor that engulfed a cyanobacterium.
119
Archegonium (pl. archegonia)
In plants, the female gametangium, a moist chamber in which gametes develop.
120
Archenteron
The endoderm-lined cavity, formed during gastrulation, that develops into the digestive tract of an animal.
121
Archosaur
Member of the reptilian group that includes crocodiles, alligators, and dinosaurs, including birds.
122
Arteriole
A vessel that conveys blood between an artery and a capillary bed.
123
Artery
A vessel that carries blood away from the heart to organs throughout the body.
124
Arthropod
A segmented ecdysozoan with a hard exoskeleton and jointed appendages. Familiar examples include insects, spiders, millipedes, and crabs. Phylum Arthropoda.
125
Artificial selection
The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits.
126
Ascocarp
The fruiting body of a sac fungus (ascomycete).
127
Ascomycete
Member of the fungal phylum Ascomycota, commonly called sac fungus. The name comes from the saclike structure in which the spores develop.
128
Ascus
A saclike spore capsule located at the tip of a dikaryotic hypha of a sac fungus.
129
Asexual reproduction
The generation of offspring from a single parent that occurs without the fusion of gametes (by budding, division of a single cell, or division of the entire organism into two or more parts). In most cases, the offspring are genetically identical to the parent.
130
Assisted migration
The translocation of a species to a favorable habitat beyond its native range for the purpose of protecting the species from human-caused threats.
131
Assisted reproductive technology
A fertilization procedure that generally involves surgically removing eggs (secondary oocytes) from a woman's ovaries after hormonal stimulation, fertilizing the eggs, and returning them to the woman's body.
132
Associative learning
The acquired ability to associate one environmental feature (such as a color) with another (such as danger).
133
Aster
A radial array of short microtubules that extends from each centrosome toward the plasma membrane in an animal cell undergoing mitosis.
134
Astrocyte
A glial cell with diverse functions including providing structural support for neurons, regulating the interstitial environment, facilitating synaptic transmission, and assisting in regulating the blood supply to the brain.
135
Atherosclerosis
A cardiovascular disease in which fatty deposits called plaques develop in the inner walls of the arteries, obstructing the arteries and causing them to harden.
136
Atom
The smallest unit of matter that retains the properties of an element.
137
atomic mass
The total mass of an atom, which is the mass in grams of 1 mole of the atom.
138
Atomic nucleus
An atom's dense central core, containing protons and neutrons.
139
Atomic number
The number of protons in the nucleus of an atom, unique for each element and designated by a superscript to the left of the elemental symbol.
140
ATP (Adenosine Triphosphate)
An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.
141
ATP synthase
A complex of several membrane proteins that functions in chemiosmosis with adjacent electron transport chains, using the energy of a hydrogen ion (proton) concentration gradient to make ATP. ATP synthases are found in the inner mitochondrial membranes of eukaryotic cells and in the plasma membranes of prokaryotes.
142
Atrial Natriuretic Peptide (ANP)
A peptide hormone secreted by cells of the atria of the heart in response to high blood pressure. ANP's effects on the kidney alter ion and water movement and reduce blood pressure.
143
Atrioventricular (AV) node
A region of specialized heart muscle tissue between the left and right atria where electrical impulses are delayed for about 0.1 second before spreading to both ventricles and causing them to contract.
144
Atrioventricular (AV) Valve
A heart valve located between each atrium and ventricle that prevents a backflow of blood when the ventricle contracts.
145
Atrium
A chamber of the vertebrate heart that receives blood when the ventricle contracts.
146
Autocrine
Referring to a secreted molecule that acts on the cell that secreted it.
147
Autoimmune disease
An immunological disorder in which the immune system turns against self.
148
Autonomic nervous system
An efferent branch of the vertebrate peripheral nervous system that regulates the internal environment; consists of the sympathetic, parasympathetic, and enteric divisions.
149
Autopolyploid
An individual that has more than two chromosomes sets that are all derived from a single species.
150
Autosome
A chromosome that is not directly involved in determining sex; not a sex chromosome.
151
Autotroph
An organism that obtains organic food molecules without eating other organisms or substances derived from other organisms or substances dervied from other organisms. Autotrophs use energy from the sun or from oxidation of inorganic substances to make organic molecules from inorganic ones.
152
Auxin
A term that primarily refers to indoleacetic acid (IAA), a natural plant hormone that has variety of effects, including cell elongation, root formation, secondary growth, and fruit growth.
153
Average heterozygosity
The percentage, on average, of a populations loci that are heterozygous in members of the population.
154
Avirulent
Describing a pathogen that can mildly harm, but not kill, the host.
155
Axillary bud
A structure that has the potential to form a lateral shoot, or branch. The bud appears in the angle formed between a leaf and a stem.
156
Axon
A typically long extension, or process, of a neuron that carries nerve impulses away from the cell body toward target cells.
157
B cells
The lymphocytes that complete their development in the bone marrow and become effector cells for the humoral immune response.
158
Bacteria
One of two prokaryotic domains, the other being Archaea.
159
Bacterial Artificial Chromosome (BAC)
A large plasmid that acts as a bacterial chromosome and can carry inserts of 100,000 to 300,000 base pairs (100-300 kB).
160
Bacteriophage
A virus that infects bacteria; also called a phage.
161
Bacteriod
A form of the bacterium Rhizobium contained within the vesicles formed by the root cells of a root nodule.
162
Balancing selection
Natural selection that maintains two or more phenotypic forms in a population.
163
Bark
All tissues external to the vascular cambium, consisting mainly of the secondary phloem and layers of periderm.
164
Barr body
A dense object lying along the inside of the nuclear envelope in cells of female mammals, representing a highly condensed, inactivated X chromosome.
165
Basal angiosperm
A member of one of three clades of early-diverging lineages of flowering plants. Examples are Amborella, water lilies, and star anise and its relatives.
166
Basal body
A eukaryotic cell structure consisting of a "9+0" arrangement of microtubule triplets. The basal body may organize the microtubule assembly of a cilium or flagellum and is structurally very similar to a centriole.
167
Basal metabolic rate (BMR)
The metabolic rate of a resting, fasting, and nonstressed endotherm at a comfortable temperature.
168
Basal taxon
In a specified group of organisms, a taxon whose evolutionary lineage diverged early in the history of the group.
169
Base
A substance that reduces the hydrogen ion concentration of a solution.
170
Basidiocarp
Elaborate fruiting body of a dikaryotic mycelium of a club fungus.
171
Basidiomycete
Member of the fungal phylum Basidiomyceta, commonly called club fungus. The name comes from the club-like shape of the basidium.
172
Basidium
A reproductive appendage that produces sexual spores on the gills of mushrooms (club fungi).
173
Batesian mimicry
A type of mimicry in which a harmless species looks like a species that is poisonous or otherwise harmful to predators.
174
Behavior
Individually, an action carried out by muscles or glands under control of the nervous system in response to a stimulus; collectively, the sum of an animal's responses to external and internal stimuli.
175
Behavioral ecology
The study of the evolution of and ecological basis for animal behavior.
176
Benign tumor
A mass of abnormal cells with specific genetic and cellular changes such that the cells are not capable of surviving at a new site and generally remain at the site of the tumor's origin.
177
Benthic zone
The bottom surface of an aquatic environment.
178
Benthos
The communities of organisms living in the benthic zone of an aquatic biome.
179
Beta (β) pleated sheet
One form of the secondary structure of proteins in which the polypeptide chain folds back and forth. Two regions of the chain lie parallel to each other and are held together by hydrogen bonds between atoms of the polypeptide backbone (not the side chain).
180
Beta oxidation
A metabolic sequence that breaks fatty acids down to two-carbon fragments that enter the citric acid cycle as acetyl CoA.
181
Bicoid
A maternal effect gene that codes for a protein responsible for specifying the anterior end in Drosophila melanogaster.
182
Bilateral symmetry
Body symmetry in which a central longitudinal plane divides the body into two equal but opposite halves.
183
Bilateran
Members of a clade of animals with bilateral symmetry and three germ layers.
184
Bile
A mixture of substances that is produced in the liver and stored in the gallbladder; enables formation of fat droplets in water as an aid in the digestion and absorption of fats.
185
Binary fission
A method of asexual reproduction by "division by half." In prokaryotes, binary fission does not involve mitosis, but in single-celled eukaryotes that undergo binary fission, mitosis is part of the process.
186
Binomial
The two-part, latinized format for naming a species, consisting of the genus and specific epithet; a binomen.
187
Biodiversity hot spot
A relatively small area with numerous endemic species and a large number of endangered and threatened species.
188
Bioenergetics
1. The overall flow and transformation of energy in an organism. 2. The study of how energy flows through organisms.
189
Biofilm
A surface-coating colony of one or more species of prokaryotes that engage in metabolic cooperation.
190
Biofuel
A fuel produced from dry organic matter or combustible oils produced by plants.
191
Biogenic amine
A neurotransmitter derived from an amino acid.
192
Biogeochemical cycle
Any of the various chemical cycles, which involve both biotic and abiotic components of ecosystems.
193
Biogeography
The study of the past and present geographic distribution of organisms.
194
Bioinformatics
The use of computers, software, and mathematical models to process and integrate biological information from large data sets.
195
Biological augmentation
An approach to restoration ecology that uses organisms to add essential materials to a degraded ecosystem.
196
Biological clock
An internal timekeeper that controls an organisms' biological rhythms. The biological clock marks time with or without environmental cues but often requires signals from the environment to remain tuned to an appropriate period. See circadian rhythm.
197
Biological magnification
A process in which retained substances become more concentrated at each higher trophic level in a food chian.
198
Biological species concept
Definition of a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable, fertile offspring with members of other such groups.
199
Biology
The scientific study of life.
200
Biomanipulation
An approach that applies the top-down model of community organization to alter ecosystem characteristics. For example, ecologists can prevent algal bolooms and eutrophication by altering the density of higher-level consumers in lakes instead of by using chemical treatments.
201
Biomass
The total mass of organic matter comprising a group of organisms in a particular habitat.
202
Biome
Any of the world's major ecosystem types, often classified according to the predominant vegetation for terrestrial biomes and the physical environment for aquatic biomes and characterized by adaptations of organisms to that particular environment.
203
Bioremediation
The use of organisms to detoxify and restore polluted and degraded ecosystems.
204
Biosphere
The entire portion of Earth inhabited by life; the sum of all the planet's ecosystems.
205
Biotechnology
The manipulation of organisms and their components to produce useful products.
206
Biotic
Pertaining to the living factors - the organisms - in an environment.
207
Bipolar cell
A neuron that relays information between photoreceptors and ganglion cells in the retina.
208
Bipolar disorder
A depressive mental illness characterized by swings of mood from high to low; also called manic-depressive disorder.
209
Birth control pill
A chemical contraceptive that inhibits ovulation, retards follicular development, or alters a woman's cervical mucus to prevent sperm from entering the uterus.
210
Blade
1. A leaflike structure of a seaweed that provides most of the surface area for photosynthesis. 2. The flattened portion of a typical leaf.
211
Blastocyst
The blastula stage of mammalian embryonic, consisting of an inner cell mass, a cavity, and an outer layer, the trophoblast. In humans, the blastocyst forms 1 week after fertilization.
212
Blastomere
An early embryonic cell arising during the cleavage stage of an early embryo.
213
Blastopore
In a gastrula, the opening of the archenteron that typically develops into the anus in deuterostomes and the mouth in protostomes.
214
Blastula
A hollow balls of cells that marks the end of the cleavage during early embryonic development in animals.
215
Blood
A connective tissue with a fluid matrix called plasma in which red blood cells, white blood cells, and cell fragments called platelets are suspended.
216
Blue-light photoreceptor
A type of light receptor in plants that initiates a variety of responses, such as phototropism and slowing of hypocotyl elongation.
217
Body cavity
A fluid- or air-filled space between the digestive tract and the body wall.
218
Body plan
In multicellular eukaryotes, a set of morphological and developmental traits that are intigrated into a functional whole - the living organism.
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Bohr shift
A lowering of the affinity of hemoglobin for oxygen, caused by a drop in pH. It facilitates the release of oxygen from hemoglobin in the vicinity of active tissues.
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Bolus
A lubricated ball of chewed food.
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Bone
A connective tissue consisting of living cells held in a rigid matrix of collagen fibers embedded in calcium salts.
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Book lung
An organ of gas exchange in spiders, consisting of stacked plates contained in an internal chamber.
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Bottleneck effect
Genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions. Typically, the surviving population is no longer genetically representative of the original population.
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Bottom-up model
A model of community organization in which mineral nutrients influence community organization by controlling plant or phytoplankton numbers, which in turn control herbivore numbers, which in turn control predator numbers.
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Bowman's capsule
A cup-shaped receptacle in the vertebrate kidney that is the initial, expanded segment of the nephron where filtrate enters from the blood.
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Brachiopod
A marine lophophorate with a shell divided into dorsal and ventral halves; also called a lamp shell.
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Brain
Organ of the central nervous system where information is processed and integrated.
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Brainstem
A collection of structures in the vertebrate brain, including the midbrain, the pons, and the medulla oblongata; functions in homeostasis, coordination of movement, and conduction of information to higher brain centers.
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Branch point
The representation on a phylogenetic tree of the divergence of two or more taxa from a common ancestor. A branch point is usually shown as a dichotomy in which a branch representing the ancestral lineage splits (at the branch point) into two branches, one for each of the two descendant lineages.
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Brassinosteroid
A steroid hormone in plants that has a variety of effects, including inducing cell elongation, retarding leaf abscission, and promoting xylem differentiation.
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Breathing
Ventilation of the lungs through alternating inhalation and exhalation.
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Bronchiole
A fine branch of the bronchi that trasports air to alveoli.
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Bronchus
One of a pair of breathing tubes that branch from the trachea into the lungs.
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Brown algae
A multicellular, photosynthetic protist with a characteristic brown or olive color that results from caretenoids in its plastids. Most brown algae are marine, and some have a plantlike body (thallus).
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Bryophyte
An informal name for a moss, liverwort, or hornwort; a nonvascular plant that lives on land but lacks some of the terrestrial adaptations of vascular plants.
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Budding
Asexual reproduction in which outgrowths from the parent form and pinch off to live independently or else remain attached to eventually form extensive colonies.
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Buffer
A solution that contains a weak acid and its corresponding base. A buffer minimizes changes in pH when acids or bases are added to the solution.
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Bulk feeder
An animal that eats relatively large pieces of food.
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Bulk flow
The movement of a fluid due to a difference in pressure between two locations.
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Bundle-sheath cells
In C4 plants, a type of photosynthetic cell arranged into tightly packed sheaths around the veins of a leaf.
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C3 Plant
A plant that uses the Calvin Cycle for the initial steps that incorporate CO2 into organic material, forming a three-carbon compound as the first stable intermediate.
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C4 Plant
A plant in which the Calvin Cycle is preceded by reactions that incorporate CO2 into a four carbon compound, the end product of which supplies CO2 for the Calvin Cycle.
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Calcitonin
A hormone secreted by the thyroid gland that lowers blood calcium levels by promoting calcium deposition in bone and calcium excretion from the kidneys, nonessential in humans.
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Callus
A mass of dividing, undifferentiated cells growing in culture.
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Calorie (cal)
The amount of heat energy required to raise the temperature of 1 g of water by 1 degree C; also the amount of heat energy that 1 g of water releases when it cools 1 degree C. The Calorie, usually used to indicate the energy content of food, is a kilocalorie.
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Calvin Cycle
The second of two major stages in photosynthesis (following the light reactions), involving the fixation of atmospheric CO2 and reduction of the fixed carbon into carbohydrate.
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CAM Plant
A plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions. In this process, carbon dioxide entering open stomata during the night is converted to organic acids, which release CO2 for the Calvin cycle during the day, when stomata are closes.
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Cambrian Explosion
A relatively brief time in geologic history when many present-day phyla of animals first appeared in the fossil record. This burst of evolutionary chage occured about 535-525 million years ago and saw the emergence of the first large, hard-bodied animals.
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Canopy
The uppermost layer of vegetation in a terrestrial biome.
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Capillary
A microscopic blood vessel that penetrates the tissues and consists of a single layer of endothelial cells that allows exchange between the blood and interstitial fluid.
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Capillary Bed
A network of capillaries in a tissue or organ.
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Capsid
The protein shell that encloses a viral genome. It may be rod-shaped, polyhedral, or more complex in shape.
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Capsule
1. In prokaryotes, a dense and well-defined layer of polysaccharide or protein that surrounds the cell wall and is sticky, protecting the cell and enabling it to adhere to substrates or other cells. 2. The sporangium of a bryophyte (moss, liverwort, or hornwort).
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Carbohydrate
A sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharide).
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Carbon fixation
The initial incorporation of carbon from CO2 into an organic compound by an autotrophic organism (a plant, another photosynthetic organism, or a chemoautotrophic prokaryote).
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Carbonyl Group
A chemical group present in aldehydes and ketones and consisting of a carbon atom double-bonded to an oxygen atom.
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Cardiac cycle
The alternating contractions and relaxations of the heart.
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Cardiac muscle
A type of striated muscle that forms the contractile wall of the heart. Its cells are joined by intercalated disks that relay the electrical signals underlying each heartbeat.
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Cardiac output
The volume of blood pumped per minute by each ventricle of the heart.
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Cardiovascular system
A closed circulatory system with a heart and branching network of arteries, capillaries, and veins. The system is characteristic of vertebrates.
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Carnivore
An animal that mainly eats other animals.
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Carotenoid
An accessory pigment, either yellow or orange, in the chloroplasts of plants and in some prokaryotes. By absorbing wavelengths of light that chlorophyll cannot, carotenoids broaden the spectrum of colors that can drive photosynthesis.
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Carpel
The ovule-producing reproductive organ of a flower, consisting of the stigma, style, and ovary.
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Carrier
In genetics, an individual who is heterozygous at a given genetic locus for a recessively inherited disorder. The heterozygote is generally phenotypically normal for the disorder but can pass on the recessive allele to offspring.
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Carrying capacity
The maximum population size that can be supported by the available resources, symbolized as K.
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Cartilage
A flexible connective tissue with an abundance of collagenous fibers embedded in chondroitin sulfate.
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Casparian strip
A water-impermeable ring of wax in the endodermal cells of plants that blocks the passive flow of water and solutes into the stele by way of cell walls.
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Catabolic pathway
A metabolic pathway that releases energy by breaking down complex molecules to simpler molecules.
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Catalyst
A chemical agent that selectively increases the rate of a reaction without being consumed in the reaction.
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Catastrophism
The principle that events in the past occurred suddenly and were caused by different mechanisms that those operating today. Contrast with Uniformitarianism.
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Catecholamine (cat-uh-coal-uh-mean)
Any of a class of neurotransmitters and hormones, including the hormones epinephrine and norepinephrine, that are synthesized from the amino acid tyrosine.
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Cation
A positively charged ion.
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Cation exchange
A process in which positively charged minerals are made available to a plant when hydrogen ions in the soil displace mineral ions from the clay particles.
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cDNA library
A gene library containing clones that carry complementary DNA (cDNA) inserts. The library includes only the genes that were transcribed in the cells whose mRNA was isolated to make the cDNA (therefore, leaves out genes that are not being transcribed/expressed).
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Cecum
The blind pouch forming one branch of the large intestine.
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Cell body
The part of the neuron that houses the nucleus and most other organelles.
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Cell cycle
An ordered sequence of events in the life of a cell, from its origin in the division of a parent cell until its own division into two. The eukaryotic cell cycle is composed of interphase (including G1, S, and G2 subphases) and M phase (including mitosis and cytokinesis).
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Cell cycle control system
A cyclically operating set of molecules in the eukaryotic cell that both triggers and coordinates key events in the cell cycle.
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Cell division
The reproduction of cells.
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Cell fractionation
The disruption of a cell and separation of its parts by centrifugation at successively higher speeds.
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Cell plate
A membrane-bounded, flattened sac located at the midline of a dividing plant cell, inside which the new cell wall forms during cytokinesis. (DO NOT confuse with metaphase plate).
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Cell wall
A protective layer external to the plasma membrane in the cells of plants, prokaryotes, fungi, and some protists. Polysaccharides such as cellulose (in plants and some protists), chitin (in fungi), and peptidoglycan (in bacteria) are important structural components of cell walls.
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Cell-mediated immune response
The branch of adaptive immunity that involves the activation of cytotoxic T cells, which defend against infected cells.
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Cellular respiration
The catabolic pathways of aerobic and anaerobic respiration, which break down organic molecules and use an electron transport chain for the production of ATP.
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Cellular slime mold
A type of protist characterized by unicellular amoeboid cells and aggregated reproductive bodies in its life cycle.
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Cellulose
A structural polysaccharide of plant cell walls, consisting of glucose monomers joined by β-glycosidic linkages.
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Celsius scale
A temperature scale (℃) equal to 5/9(℉ - 32) that measures the freezing point of water at 0℃ and the boiling point of water at 100℃.
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Central canal
The narrow cavity in the center of the spinal cord that is continuous with the fluid-filled ventricles of the brain.
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Central nervous system (CNS)
The portion of the nervous system where signal integration occurs; in vertebrate animals, the brain and spinal cord.
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Central vacuole
In a mature plant cells, a large membranous sac with diverse roles in growth, storage, and sequestration of toxic substances.
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Centriole
A structure in the centrosome of an animal cell composes of a cylinder of microtubule triplets arranged in a 9+0 pattern. A centrosome has a pair of centrioles.
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Centromere
In a duplicated chromosome, the region on each sister chromatid where they are most closely attached to each other by proteins that bind to specific DNA sequences; this close attachment causes a constriction in the condensed chromosome. (An uncondensed, unduplicated chromosome has a single centromere, identified by its DNA sequence.)
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Cephalization
An evolutionary trend toward the concentration of sensory equipment at the anterior end of the body.
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Cercozoan
An amoeboid or flagellated protist that feeds with threadlike pseudopodia.
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Cerebellum
Part of the vertebrate hindbrain located dorsally; functions in unconscious coordination of movement and balance.
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Cerebral cortex
The surface of the cerebrum; the largest and most complex part of the mammalian brain, containing nerve cell bodies of the cerebrum; the part of the vertebrate brain most changed through evolution.
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Cerebral hemisphere
The right or left side of the cerebrum.
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Cerebrum
The dorsal portion of the vertebrate forebrain, composed of right and left hemispheres; the integrating center for memory, learning, emotions, and other highly complex functions of the central nervous system.
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Cervix
The neck of the uterus, which opens into the vagina.
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Chaparral
A scrubland biome of dense, spiny evergreen shrubs found at midlatitudes along coasts where cold ocean currents circulate offshore; characterized by mild, rainy winters and long, hot, dry summers.
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Chaperonin
A protein complex that assists in the proper folding of other proteins.
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Characteristic
An observable heritable feature that may vary among individuals.
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Character displacement
The tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species.
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Checkpoint
A control point in the cell cycle where stop and go-ahead signals can regulate the cycle.
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Chelicera (pl. Chelicerae)
One of a pair of clawlike feeding appendages characteristic of chelicerates.
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Chelicerate
An arthropod that has chelicerae and a body divided into a cephalothorax and an abdomen. Living chelicerates include sea spiders, horseshoe crabs, scorpions, ticks, and spiders.
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Chemical bond
An attraction between two atoms, resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms. The bonded atoms gain complete outer electron shells.
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Chemical energy
Energy available in molecules for release in a chemical reaction; a form of potential energy.
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Chemical equilibrium
In a chemical reaction, the state in which the rate of the forward reaction equals the rate of the reverse reaction, so that the relative concentrations of the reactants and products do not change with time.
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Chemical reaction
The making and breaking of chemical bonds, leading to changes in the composition of matter.
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Chemiosmosis
An energy-coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane to drive cellular work, such as the synthesis of ATP. Under aerobic conditions, most ATP synthesis in cells occurs by chemiosmosis.
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Chemoautotroph
An organism that obtains energy by oxidizing inorganic substances and needs only carbon dioxide as a carbon source.
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Chemoheterotroph
An organism that requires organic molecules for both energy and carbon.
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Chemoreceptor
A sensory receptor that responds to a chemical stimulus, such as a solute or an odorant.
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Chiasma
The X-shaped, microscopically visible region where crossing over has occurred earlier in prophase I between homologous nonsister chromatids. Chiasmata become visible after synapsis ends, with the two homologs remaining associated due to sister chromatid cohesion.
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Chitin
A structural polysaccharide, consisting of amino sugar monomers, found in many fungal cell walls and in the exoskeletons of all arthropods.
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Chlorophyll
A green pigment located in membranes within the chloroplasts of plants and algae and in the membranes of certain prokaryotes. Chlorophyll a participates directly in the light reactions, which convert solar energy to chemical energy.
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Chlorophyll A
A photosynthetic pigment that participates directly in the light reactions, which convert solar energy to chemical energy.
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Chlorophyll B
An accessory photosynthetic pigment that transfers energy to chlorophyll A.
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Chloroplast
An organelle found in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.
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Choanocyte
A flagellated feeding cell found in sponges. Also called a collar cell, it has a collar-like ring that traps food particles around the base of its flagellum.
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Cholesterol
A steroid that forms an essential component of animal cell membranes and acts as a precursor molecule for the synthesis of other biologically important steroids, such as many hormones.
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Chondrichthyan
Member of the class Chondrichthyes, vertebrates with skeletons made mostly of cartilage, such as sharks and rays.
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Chordate
Member of the phylum Chordata, animals that at some point during their development have a notochord; a dorsal, hollow nerve cord; pharyngeal slits or clefts; and a muscular, post-anal tail.
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Chorionic villus sampling (CVS)
A technique associated with prenatal diagnosis in which a small sample of the fetal portion of the placenta is removed for analysis to detect certain genetic and congenital defects in the fetus.
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Chromalveolata
One of the five supergroups of eukaryotes proposed in a current hypothesis of the evolutionary lineage of eukaryotes. Chromalveolates may have originated by secondary endosymbiosis and include two large protist clades, the alveolates and the stramenopiles.
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Chromatin
The complex of DNA and proteins that makes up eukaryotic chromosomes. When the cell is not dividing chromatin exists in the dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope.
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Chromosome
A cellular structure carrying genetic material, found in the nucleus of eukaryotic cells. Each chromosome consists of one very long DNA molecule and associated proteins. (A bacterial chromosome usually consists of a single circular DNA molecule and associated proteins. Found in the nucleoid region.)
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Chromosome theory of inheritence
A basic principle in biology stating that genes are located at specific positions (loci) on chromosomes during meiosis accounts for inheritance patterns.
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Chylomicron
A lipid transport globule composed of fats mixed with cholesterol and coated with proteins.
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Chyme
The mixture of partially digested food and digestive juices formed in the stomach.
