324 ❯ Glossary
Golgi apparatusOrganelle that modifies proteins,
lipids, and other macromolecules by the addition of
sugars and other molecules to form glycoproteins.
The products are then sent to other parts of the cell.
G-proteins Proteins vital to signal cascade pathways.
These proteins directly activate molecules such as
adenyl cyclase to assist in a reaction.
gradualismThe theory that evolutionary change is a
steady, slow process.
granaFlattened channels and disks arranged in
stacks found in the thylakoid membrane.
gravitropismA plant’s growth response to gravita-
tional force. Auxin and gibberellins are involved in
this response.
gross productivity The difference over time
between the dissolved oxygen concentrations of
the light and dark bottles calculated in primary
productivity experiments.
growth factors Assist in the growth of structures.
guard cells Cells within the epidermis of plants that
control the opening and closing of the stomata.
gymnosperm First major seed plant to evolve.
Heterosporous plant that usually transports its
sperm through the use of pollen. Conifers are the
major gymnosperm to know.
habituationLoss of responsiveness to unimportant
stimuli that do not provide appropriate feedback.
haploid (n)An organism that has only one copy of
each type of chromosome.
Hardy-Weinberg equilibrium A special case where a
population is in stasis, or not evolving.
helicaseEnzyme that unzips DNA, breaking the
hydrogen bonds between the nucleotides and pro-
ducing the replication fork for replication.
helper T cell Immune cells that assist in activation of
B cells.
hemoglobin Molecule that allows red blood cells to
carry and deliver oxygen throughout the body to
hardworking organs and tissues.
hemophilia Sex-linked disorder caused by the
absence of a protein vital to the clotting process.
Individuals with this condition have difficulty
clotting blood after even the smallest of wounds.
herbivoreConsumer that obtains energy and nutri-
ents through consumption of plants.
heterosporous plantPlant that produces two types
of spores, male and female.
heterotroph An organism that must consume other
organisms to obtain nourishment. They are the
consumers of the world.
heterotroph theoryTheory that posits that the first
organisms were heterotrophs (organisms that
cannot produce their own food).
heterozygote advantageThe situation, such as sickle
cell anemia in malarial regions, in which being het-
erozygous for a condition provides some benefit.
heterozygous (hybrid) An individual is heterozy-
gous (or a hybrid) for a gene if the two alleles are
different (Bb).
histamineChemical signal responsible for initiation
of the inflammation response of the immune system.
holandric trait A trait inherited via the Y chromosome.
homeoboxDNA sequence of a homeotic gene that
tells the cell where to put body structures.
homeotic genes Genes that regulate or “direct” the
body plan of organisms.
homologous characters Traits are said to be homol-
ogous if they are similar because their host organ-
isms arose from a common ancestor.
homologous chromosomes Chromosomes that
resemble one another in shape, size, function, and
the genetic information they contain. They are not
identical.
homosporous plant Plants that produce a single
spore type that gives rise to bisexual gametophytes.
homozygous (pure) An individual is homozygous
for a gene if both of the given alleles are the same
(BB or bb).
honest indicators Sexually selected traits that are the
result of female choice and signal genetic quality.
hormones Chemicals produced by glands such as
the pituitary and used by the endocrine system to
signal distant target cells.
host range The range of cells that a virus is able to
infect. For example, HIV infects the T cells of
our body.
humoral immunity Immunity involving antibodies
and circulating fluids.
Huntington’s disease An autosomal dominant
degenerative disease of the nervous system that
shows itself when a person is in their 30s or 40s
and is both irreversible and fatal.
hybrid vigor Refers to the fact that hybrids may have
increased reproductive success compared to inbred
strains. This is due to the fact that inbreeding