5\u2032 cap – A modified form of guanine nucleotide added onto the 5\u2032 end of a pre-mRNA
molecule.
A site – 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.)
ABC hypothesis – A model of flower formation identifying three classes of organ identity
genes that direct formation of the four types of floral organs.
abiotic – Nonliving; referring to the physical and chemical properties of an environment.
abortion – The termination of a pregnancy in progress.
abscisic acid (ABA) – 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.
absorption – The third stage of food processing in animals: the uptake of small nutrient
molecules by an organism’s body.
absorption spectrum – The range of a pigment’s ability to absorb various wavelengths of
light; also a graph of such a range.
abyssal zone – The part of the ocean’s benthic zone between 2,000 and 6,000 m deep.
acanthodian – Any of a group of ancient jawed aquatic vertebrates from the Silurian and
Devonian periods.
accessory fruit – A fruit, or assemblage of fruits, in which the fleshy parts are derived
largely or entirely from tissues other than the ovary.
acclimatization – Physiological adjustment to a change in an environmental factor.
acetyl coenzyme A (acetyl CoA) – The entry compound for the citric acid cycle in cellular
respiration, formed from a fragment of pyruvate attached to a coenzyme.
acetylcholine – 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.
acid – A substance that increases the hydrogen ion concentration of a solution.
acid precipitation – Rain, snow, or fog that is more acidic than pH 5.2.
acoelomate – A solid-bodied animal lacking a cavity between the gut and outer body
wall.
acrosomal reaction – The discharge of hydrolytic enzymes from the acrosome, a vesicle
in the tip of a sperm, when the sperm approaches or contacts an egg.
acrosome – A vesicle in the tip of a sperm containing hydrolytic enzymes and other
proteins that help the sperm reach the egg.
actin – A globular protein that links into chains, two of which twist helically about each
other, forming microfilaments in muscle and other kinds of cells.
action potential – An electrical signal that propagates (travels) along the membrane of a
neuron or other excitable cell as a nongraded (all-or-none) depolarization.
action spectrum – A graph that profiles the relative effectiveness of different
wavelengths of radiation in driving a particular process.
activation energy – The amount of energy that reactants must absorb before a chemical
reaction will start; also called free energy of activation.
activator – A protein that binds to DNA and stimulates gene transcription. In prokaryotes,
they bind in or near the promoter; in eukaryotes, they generally bind to control elements
in enhancers.
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. It can develop as a
result of natural infection or immunization.
active site – The specific region of an enzyme that binds the substrate and that forms
the pocket in which catalysis occurs.
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.
adaptation – Inherited characteristic of an organism that enhances its survival and
reproduction in a specific environment.
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.
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.
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.
adenylyl cyclase – An enzyme that converts ATP to cyclic AMP in response to an
extracellular signal.
adhesion – The clinging of one substance to another, such as water to plant cell walls by
means of hydrogen bonds.
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.
adrenocorticotropic 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.
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.
age structure – The relative number of individuals of each age in a population.
aggregate fruit – A fruit derived from a single flower that has more than one carpel.
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.
alcohol fermentation – Glycolysis followed by the reduction of pyruvate to ethyl alcohol,
regenerating NAD+ and releasing carbon dioxide.
aldosterone – A steroid hormone that acts on tubules of the kidney to regulate the
transport of sodium ions (Na+) and potassium ions (K+).
algae – A diverse grade of photosynthetic protists, including unicellular and multicellular
forms. These species are included in three of the five eukaryote supergroups
(Chromalveolata, Rhizaria, and Archaeplastida).
alimentary canal – A complete digestive tract, consisting of a tube running between a
mouth and an anus.
allele – Any of the alternative versions of a gene that may produce distinguishable
phenotypic effects.
allergen – An antigen that triggers an exaggerated immune response.
allopatric speciation – The formation of new species in populations that are
geographically isolated from one another.
allopolyploid – A fertile individual that has more than two chromosome sets as a result of
two different species interbreeding and combining their chromosomes.
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.
alpha (\u03b1) 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).
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.
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.
altruism – Selflessness; behavior that reduces an individual’s fitness while increasing the
fitness of another individual.
alveolates – A protist with membrane-bounded sacs (alveoli) located just under the
plasma membrane.
alveolus – One of the dead-end air sacs where gas exchange occurs in a mammalian
lung.
Alzheimer’s disease – An age-related dementia (mental deterioration) characterized by
confusion and memory loss<\/p>\n\n\n\n
Download full exam here https:\/\/learnexams.com\/search\/study?query=<\/a><\/p>\n\n\n\n