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Biology LibreTexts

25.24: Glossary: G

  • Page ID
  • Galápagos Islands

    group of 16 small volcanic islands in the Pacific Ocean 966 kilometers (600 miles) off the west coast of South America, where Charles Darwin made some of his most important observations during his voyage on the HMS Beagle


    sac-like organ that stores bile from the liver and secretes it into the duodenum of the small intestine as needed for digestion


    reproductive cell produced during meiosis that has the haploid number of chromosomes; sperm or egg


    development of a haploid cell into a gamete (either sperm or egg)

    ganglion (plural, ganglia)

    type of nervous tissue that acts as a relay point for messages transmitted through nerves of the peripheral nervous system

    gas exchange

    biological process through which gases are transferred across cell membranes to either enter or leave the blood


    acute and usually self-limiting infection of the gastrointestinal tract by pathogens; also known as infectious diarrhea

    gastrointestinal (GI) tract

    organs of the digestive system through which food passes during digestion, including the mouth, pharynx, esophagus, stomach, and small and large intestines


    process in which the two-layer embryonic disc develops a third cell layer (mesoderm) and a primitive gut


    unit of DNA on a chromosome that may be encoded with the instructions for a protein

    gene cloning

    process of isolating and making copies of a gene

    gene expression

    use of a gene to make a protein

    gene flow

    change in allele frequencies that occurs when individuals move into or out of a population

    gene pool

    all the genes in all of the members of a population


    organism that can thrive in a wide variety of environments and make use of a variety of different resources, such as consuming many different types of food

    general sense

    sense of touch, which lacks specialized sensory organs and is monitored instead by sensory receptors all over the body

    gene theory

    theory that many of the characteristics of living things are controlled by genes that are passed from parents to offspring

    gene therapy

    experimental method of curing genetic disorders by inserting normal genes into cells with mutant genes

    genetic code

    universal code of three-base codons that encodes genetic instructions for the amino acid sequences of proteins

    genetic disorder

    disease, syndrome, or other abnormal condition caused by a mutation in one or more genes or by a chromosomal alteration

    genetic drift

    random change in allele frequencies that occurs in a small population

    genetic engineering

    using biotechnology to change the genetic makeup of an organism


    science of heredity

    genetic trait

    characteristic that is encoded in DNA

    genital herpes

    sexually transmitted infection caused by herpes simplex virus (usually HSV-2) that is characterized by periodic outbreaks of blisters on the genitals

    genital warts

    small, rough growths on the genitals caused by a sexually transmitted infection with human papillomavirus (HPV)


    alleles an individual inherits at a particular genetic locus


    taxon above the species in the Linnaean classification system; group of closely related species

    geologic time scale

    timeline of Earth based on major events in geology, climate, and the evolution of life

    geothermal energy

    renewable, nonpolluting source of energy that can be obtained from Earth’s naturally occurring internal heat

    germinal stage

    earliest and shortest stage of the human lifespan, lasting about a week from fertilization until the new organism implants in the endometrium of the uterus

    germline mutation

    mutation that occurs in a gamete

    germ theory of disease

    theory that contagious diseases are caused by the transmission of microorganisms that grow and reproduce in their hosts and make them sick

    gestational carrier

    woman who agrees to receive a transplanted embryo from a couple, carry it to term, and then give the infant to the couple after birth


    hormone produced in the stomach and small intestine that normally stimulates appetite


    type of gastroenteritis caused by a single-celled protozoan parasite named Giardia lambliathat typically spreads through contaminated food or water via a fecal-oral route

    glial cell

    nervous tissue cell that provides support for neurons and helps them transmit nerve impulses

    global warming

    recent rise in Earth’s average surface temperature generally attributed to an enhanced greenhouse effect caused mainly by human actions

    glomerulus (plural, glomeruli)

    network of capillaries in the nephron of a kidney where substances are filtered out of the blood


    endocrine hormone secreted by alpha cells of the pancreas that signals cells to break down stored glycogen to glucose, thereby increasing the level of blood glucose


    simple six-carbon sugar, or monosaccharide, that is the nearly universal food for life

    glucose-6-phosphate dehydrogenase (G6PD)

    red blood cell enzyme involved in metabolizing glucose, deficiency in which is a genetic adaptation to malaria


    complex carbohydrate (polysaccharide) that animals use to store energy


    first stage of cellular respiration in which glucose is split, in the absence of oxygen, to form two molecules of pyruvate (pyruvic acid) and two (net) molecules of ATP


    abnormal enlargement of the thyroid gland

    Golgi apparatus

    organelle in eukaryotic cells that processes proteins and prepares them for use both inside and outside the cell


    one of a pair of organs that secrete sex hormones and produce gametes; testis in males and ovary in females


    common sexually transmitted infection that is caused by the bacterium Neisseria gonorrhoeae


    model of the timing of evolution in which evolutionary change occurs at a slow and steady pace

    Grave’s disease

    autoimmune disorder in which abnormal antibodies produced by the immune system stimulate the thyroid gland to secrete excessive quantities of its hormones

    gray matter

    type of nervous tissue that is found only in the brain and spinal cord and that is important for information processing

    greenhouse effect

    natural feature of Earth’s atmosphere that occurs when greenhouse gases in the atmosphere absorb and re-radiate heat back down to Earth’s surface, making the surface temperature warmer than it otherwise would be

    greenhouse gas

    naturally occurring or anthropogenic gas such as carbon dioxide that allows the greenhouse effect to warm Earth’s surface

    green revolution

    worldwide advances in agriculture, including increased use of machinery and chemicals, that occurred between 1950 and 1984 and greatly increased global food production


    fresh water that exists in the ground, either in the soil or in rock layers below the surface

    growing season

    period of time each year when it is warm enough and wet enough for plants to grow

    growth hormone

    hormone secreted by the anterior pituitary gland that stimulates growth in cells all over the body