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sacs that sort, chemically modify, and package proteins produced on the rough
endoplasmic reticulum.
gonadotropin-releasing hormone (GnRH) A hormone produced by the
hypothalamus that controls the secretion of luteinizing hormone.
gonadotropins Hormones produced by the anterior pituitary that affect the testis
and ovary; include follicle-stimulating hormone and luteinizing hormone.
gonads The male and female sex organs.
Gondwana Name applied to the ancient (Paleozoic-early Mesozoic) southern
hemisphere supercontinent that rifted apart to form present-day Antarctica,
India, Africa, Australia, and South America. The southern part of Pangaea.
gonorrhea A sexually transmitted disease that is caused by a bacterium that
inþames and damages epithelial cells of the reproductive system.
grana A series of stacked thylakoid disks containing chlorophyll; found in the
inner membrane of chloroplasts.
grasslands biome Occurs in temperate and tropical regions with reduced
rainfall or prolonged dry seasons; characterized by deep, rich soil, an absence
of trees, and large herds of grazing animals.
green algae Common name for algae placed in the division Chlorophyta.
greenhouse effect The heating that occurs when gases such as carbon dioxide
trap heat escaping from the Earth and radiate it back to the surface; so-called
because the gases are transparent to sunlight but not to heat and thus act like the
glass in a greenhouse.
ground system Plant tissue system, composed mainly of parenchyma cells with
some collenchyma and sclerenchyma cells, that occupies the space between the
epidermis and the vascular system; is involved in photosynthesis, water and food
storage, and support; one of the four main tissue systems in plants.
growth hormone (GH) A peptide hormone produced by the anterior pituitary
that is essential for growth.
growth rings Features of woody stems produced by plants growing in areas
with seasonal (as opposed to year-long) growth. The growth ring marks the
position of the vascular cambium at the cessation of the previous year's growth.
guard cells Specialized epidermal cells that flank stomates and whose opening
and closing regulates gas exchange and water loss. |
guanine One of the nitrogenous bases in nucleic acids, guanine is one of the two
purine bases.
gymnosperms Flowerless, seed-bearing land plants; the Þrst seed plants;
living groups include the pines, ginkgos, and cycads. Naked seeds.
gynoecium Collective term for all of the carpels (or pistils) in a flower. Some
flowers have many pistils that are partially or wholly fused.
H
habitat disruption A disturbance of the physical environment in which a
population lives.
hair bulb The base of a hair; contains cells that divide mitotically to produce
columns of hair cells.
hair root The portion of a hair that extends from the skin's surface to the hair
bulb.
hair shaft The portion of a hair that extends above the skin's surface.
half-life The time required for one-half of an original unstable radioactive
element to be converted to a more stable daughter element.
halophiles A group of archaebacteria that are able to tolerate high salt
concentrations.
haploid Cells that contain only one member of each homologous pair of
chromosomes (haploid number = n). At fertilization, two haploid gametes fuse to
form a single cell with a diploid number of chromosomes.
hardwoods Term applied to dicot trees, as opposed to softwoods, a term
applied to gymnosperms.
Haversian canal The central opening of compact bone; contains nerves and
blood vessels.
heart The multicellular, chambered, muscular structure that pumps blood
through the circulatory system by alternately contracting and relaxing.
heartwood Inner rings of xylem that have become clogged with metabolic by-
products and no longer transport water; visible as the inner darker areas in the
cross section of a tree trunk.
helper T cells A type of lymphocyte that stimulates the production of antibodies
by activating B cells when an antigen is present.
hemizygous Having one or more genes that have no allele counterparts.
Usually applied to genes on the male's X chromosome (in humans).
hemoglobin A red pigment in red blood cells that can bind with oxygen and is
largely responsible for the blood's oxygen-carrying capacity. Hemoglobin is
composed of four polypeptide chains, two alpha (±) and two beta (²) chains.
hemophilia A human sex-linked recessive genetic disorder that results in the
absence of certain blood-clotting factors, usually Factor VII. Hemophiliacs
suffer from an inability to clot their blood.
hepatitis B A potentially serious viral disease that affects the liver; can be
transmitted through sexual contact or through contact with infected blood.
herbaceous Term applied to a nonwoody stem/plant with minimal secondary
growth.
herbivores Term pertaining to a heterotroph, usually an animal, that eats plants
or algae. Herbivores function in food chains and food webs as primary consumers.
heterogametic sex The sex with two different chromosomes, such as males in
humans and Drosophila. [ Pobierz całość w formacie PDF ]