10Th Chem G

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G0 phase the nondividing state that a cell may enter instead of completing the cell cycle

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G0 phase

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G1 phase the first growth period of interphase, prior to DNA synthesis

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G1 phase

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G2 phase the second growth period of interphase, starting at the end of DNA synthesis and ending when mitosis begins

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G2 phase

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galaxy a collection of stars, dust, and gas bound together by gravity

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galaxy

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Galilean moon any one of the four largest satellites of Jupiter—Io, Europa, Ganymede, and Callisto—that were discovered by Galileo in 1610

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Galilean moon

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gallbladder a sac-shaped organ that stores bile produced by the liver

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gallbladder

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galvanometer an instrument that detects, measures, and determines the direction of a small electric current

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galvanometer

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gametangium a cell or an organ that produces gametes

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gametangium

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gamete a haploid reproductive cell that unites with another haploid reproductive cell to form a zygote

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gamete

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gametocyte a cell that is not differentiated and that develops into a gamete

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gametocyte

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gametophyte in alternation of generations, the phase in which gametes are formed; a haploid individual that produces gametes

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gametophyte in alternation of generations,

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gamma decay the release of gamma rays from the nucleus of an atom

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gamma decay

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gamma ray the high-energy photon emitted by a nucleus during fission and radioactive decay

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gamma ray

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ganglion a mass of nerve cells

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ganglion

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gas a form of matter that does not have a definite volume or shape

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gas

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gas giant a planet that has a deep, massive atmosphere, such as Jupiter, Saturn, Uranus, or Neptune

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gas giant

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gas laws the laws that state the mathematical relationships between the volume, temperature, pressure, and quantity of a gas

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gas laws

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gasohol a mixture of gasoline and alcohol that is used as a fuel

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gasohol

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gastric cecum a pouch that branches from the digestive tract of an insect

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gastric cecum

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gastric fluid a liquid secreted by gastric glands in the stomach

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gastric fluid

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gastrin a hormone that stimulates the stomach to secrete hydrochloric acid and pepsin

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gastrin

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gastrodermis In cnidarians, the layer of cells surrounding the digestive tract

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gastrodermis

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gastrointestinal tract the digestive tract from the mouth to the anus, including the stomach and intestines

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gastrointestinal tract

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gastrolith a stone that is found within the digestive system of certain animals and that helps grind food in digestion

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gastrolith

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gastropod a mollusk that has a well-developed head and a flattened foot, such as a snail, slug, or conch

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gastropod

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gastrovascular cavity a cavity that serves both digestive and circulatory purposes in some cnidarians

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gastrovascular cavity

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gastrula the embryo in the stage of development after the blastula; contains the embryonic germ layers

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gastrula

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gastrulation the transformation of the blastula into the gastrula or the formation of the embryonic germ layers

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gastrulation

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Gay-Lussac's law the law that states that the volume occupied by a gas at a constant pressure is directly proportional to the absolute temperature

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Gay-Lussac's law

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Gay-Lussac's law of combining volumes of gases the law that states that the volumes of gases involved in a chemical change can be represented by the ratio of small whole numbers

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Gay-Lussac's law of combining volumes of gases

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Geiger-Muller counter an instrument that detects and measures the intensity of radiation by counting the number of electric pulses that pass between the anode and the cathode in a tube filled with gas

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Geiger-Muller counter

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gel electrophoresis a technique used to separate nucleic acids or proteins according to size and charge in an agarose or acryl amide gel

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gel electrophoresis a

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gem mule an asexual reproductive structure produced by some freshwater sponges

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gemstone a mineral, rock, or organic material that can be used as jewelry or an ornament when it is cut and polished

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gemstone

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gene a segment of DNA that is located in a chromosome and that codes for a specific hereditary trait

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gene

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gene cloning the process of isolating a gene sequence in the genome of an organism and inserting the gene sequence into a plasmid vector for production in large numbers

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gene cloning

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gene expression The manifestation of the genetic material of an organism in the form of specific traits

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gene expression

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gene flow the movement of genes into or out of a population due to interbreeding

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gene flow

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gene pool all of the genes of the reproductively active members of a population

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gene pool

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generalist a species that has a broad niche such that the species can tolerate a wide range of conditions and can use a variety of resources

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generalist

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generation time the period between the birth of one generation and the birth of the next generation

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generation time

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generative cell in a pollen grain, the cell that divides mitotic ally and forms two sperm cells

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generator a machine that converts mechanical energy into electrical energy

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generator

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gene therapy a technique that places a gene into a cell to correct a hereditary disease or to improve the genome

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gene therapy

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genetic code the rule that describes how a sequence of nucleotides, read in groups of three consecutive nucleotides (triplets) that correspond to specific amino acids, specifies the amino acid sequence of a protein

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genetic code

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genetic counseling the process of testing and informing potential parents about their genetic makeup and the likelihood that they will have offspring with genetic defects or hereditary diseases

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genetic counseling

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genetic disorder an inherited disease or disorder that is caused by a mutation in a gene or by a chromosomal defect

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genetic disorder

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genetic drift the random change in allele frequency in a population

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genetic drift

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genetic engineering a technology in which the genome of a living cell is modified for medical or industrial use

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genetic engineering

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genetic equilibrium the stability of gene frequencies in a population across generations

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genetic equilibrium

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genetic marker a gene whose phenotype is easily identified

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genetic marker

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genetic recombinationthe regrouping of genes in an offspring that results in a genetic makeup that is different from that of the parents

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genetic recombination

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genetics the science of heredity and of the mechanisms by which traits are passed from parents to offspring

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genetics

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genetic screening an examination of a person's genetic makeup

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genetic screening

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genital herpes a sexually transmitted disease that is caused by a herpes simplex virus

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genital herpes

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genome the complete genetic material contained in an individual

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genome

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genomic library a set of cloned fragments of DNA that together represent the entire genome

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genomic library

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genotype the entire genetic makeup of an organism; also the combination of genes for one or more specific traits

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genotype

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genotypic ratio the ratio of the genotypes that appear in offspring

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genotypic ratio

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genus the level of classification that comes after family and that contains similar species

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genus

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geocentric describes something that uses the Earth as the reference point

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geocentric

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geographic information system an automated system for capturing, storing, retrieving, analyzing, manipulating, and displaying geographic data (abbreviation, GIS)

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geographic information system

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geographic isolation the physical separation of populations due to geographic barriers that prevent interbreeding

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geographic isolation

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geologic column an ordered arrangement of rock layers that is based on the relative ages of the rocks and in which the oldest rocks are at the bottom

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geologic column

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geologic time scale the standard method used to divide the Earth's long natural history into manageable parts

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geologic time scale

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geology the scientific study of the origin, history, and structure of Earth and the processes that shape Earth

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geology

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geomagnetic poles a point on the Earth's surface above a pole of the Earth's imaginary internal magnet

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geomagnetic poles

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geometric isomers compounds that exist in two or more geometrically different configurations

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geometric isomers

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the mostly solid, rocky part of the Earth; extends from the center of the core to the surface of the crust

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geosphere

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geostationary orbit an orbit that is about 36,000 km above Earth's surface and in which a satellite is above a fixed spot on the equator

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geostationary orbit

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geosynchronous orbit an orbit in which a satellite moves in the same direction as Earth's rotation such that the satellite remains at an altitude or 35,880 km above Earth's surface

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geosynchronous orbit

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geothermal energy the energy produced by heat within Earth

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geothermal energy

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germination the beginning of growth or development in a seed, spore, or zygote, especially after a period of inactivity

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germination

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one of the three cell layers present in an embryo

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germ layer

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germ plasm hereditary material (chromosomes and genes) that is usually contained in the protoplasm of germ cells

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germ plasm

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gestation In mammals, the process of carrying young from fertilization to birth

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gestation

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gestation period in mammals, the length of time between fertilization and birth

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gestation period

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geysers a hot spring that periodically discharges hot water and steam

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geysers

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giant a very large and bright star whose hot core has used most of its hydrogen

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giant

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giardiasis an illness caused by the parasitic protozoan Giardia and characterized by diarrhea

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giardiasis

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gibberellins a plant hormone that stimulates growth of stems and leaves

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gibberellins

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gill in mushrooms, a structure that is located on the underside of the cap and bears the spores

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gill in mushrooms,

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gill in aquatic animals, a respiratory structure that consists of many blood vessels surrounded by a membrane that allows for gas exchange

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gill in aquatic animals,

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gill arch one of the jointed and cartilaginous or bony structures behind the jaws in fish and larval amphibians

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gill arch

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gill slit a perforation between two gill arches through which water taken in through the mouth of a fish passes over the gills and out of the fish's body

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gill slit

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gizzard an enlargement of the digestive tract of some invertebrates, such as annelids and insects, that grinds food; a muscular region in the digestive tract of birds that grinds and softens food

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gizzard

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glacial drift the rock material carried and deposited by glaciers

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glacial drift

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glacial period a period of cooler climate that occurs during an ice age and that is characterized by the advancement of glaciers

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glacial period

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glacier a large mass of moving ice

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glacier

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gland a group of cells that make special chemicals for the body

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gland

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global ocean the body of salt water that covers nearly three-fourths of Earth’s surface

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global ocean

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global positioning system a network of satellites that orbit the Earth to measure positions on the Earth's surface (abbreviation, GPS)

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global positioning system

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global warming a gradual increase in the average global temperature that is due to a higher concentration of gases such as carbon dioxide in the atmosphere

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global warming

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globular cluster a tight group of stars that looks like a ball and contains up to 1 million stars

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globular cluster

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glomerulus a cluster of capillaries that is enclosed in a Bowman's capsule in a nephron of the kidney, where blood is filtered

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glomerulus

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glucagon a hormone that is produced in the pancreas and that raises the blood glucose level

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glucagon

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glycolysis the anaerobic breakdown of glucose pyruvic acid, which makes a small amount of energy available to cells in the form of ATP

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glycolysis

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glycoprotein a protein to which carbohydrate molecules are attached

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glycoprotein

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gnomonic projection a map projection in which the points on the surface of a sphere are projected from the center of the sphere onto a plane that is tangent to the sphere

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gnomonic projection

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goiter an enlargement of the thyroid gland that causes the neck to swell

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goiter

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Golgi complex a cell organelle that helps make and package materials to be transported out of the cell

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Golgi complex

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gonad an organ that produces gametes

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gonad

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Gondwanaland the southern landmass that supposedly fragmented millions of years ago to form South America, Africa, India, Australia, and Antarctica

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Gondwanaland

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gonorrhea a sexually transmitted disease that is caused by bacteria and that results in inflammation of the mucous membranes in the urinary and reproductive tracts

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gonorrhea

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graben a long, narrow crustal block between two parallel faults

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graben

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gradient the change in elevation over a given distance

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gradient

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gradualism a model of evolution in which gradual change over a long period of time leads to biological diversity

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gradualism

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grafting a technique in which a portion of one plant is attached to the root or shoot of another plant and grows there

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grafting

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Graham's law of diffusion the law that states that the rate of diffusion of a gas is inversely proportional to the square root of the gas's density

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Graham's law of diffusion

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grain the edible seed or seed like fruit of a cereal grass

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grain

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Gram-negative bacterium a bacterium that loses the Gram stain and usually has an outer covering on its cell wall

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Gram-negative bacterium

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Gram-positive bacterium a bacterium that retains the Gram stain and usually lacks an outer covering on its cell wall

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Gram-positive bacterium

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Gram stain a series of dyes used to classify bacteria; depending on the chemistry of the bacterial cell wall, bacteria will either retain or lose the stain

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Gram stain

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granum a stack of hyaloids in a chloroplast

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granum

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graphite a soft, black, crystalline form of carbon that is a fair conductor of electricity

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graphite

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gravitational force the force of attraction between massive bodies that is due to gravitation

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gravitational force

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gravitational potential energy the potential energy stored in the gravitational fields of interacting bodies

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gravitational potential energy

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gravitropism the growth of a plant in a particular direction in response to gravity

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gravitropism

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gravity a force of attraction between objects that is due to their masses and that decreases as the distance between the objects increases

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gravity

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great ape an ape whose face has little hair and whose hands have nails and complex fingerprints, such as an orangutan, gorilla, or chimpanzee

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great ape

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great circle any circle that divides the globe in half; represents the shortest distance between any two points on the Earth's surface

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great circle

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green gland an excretory organ of some crustaceans that is located at the base of the antennae

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green gland

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greenhouse effect the warming of the surface and lower atmosphere of Earth that occurs when carbon dioxide, water vapor, and other gases in the air absorb and reradiate infrared radiation

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greenhouse effect

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greenhouse gases a gas composed of molecules that absorb and radiate infrared radiation from the sun

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greenhouse gases

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Gregorian calendar the calendar that is used in the modern industrial world and in which a year consists of 365 days (plus one extra day every four years) and years are numbered from the birth of Jesus Christ

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Gregorian calendar

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gross primary productivity the rate at which organic matter is assimilated by plants and other producers during a period of time over a certain area

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gross primary productivity

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ground moraine the rock debris left by a glacier or ice sheet

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ground moraine

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ground state the lowest energy state of a quantized system

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ground state

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ground tissue a type of plant tissue other than vascular tissue that makes up much of the inside of a plant

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ground tissue

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groundwater the water that is beneath the Earth's surface

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groundwater

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group a vertical column of elements in the periodic table; elements in a group share chemical properties

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group

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growth factor a substance that is needed to allow cell multiplication

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growth factor

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growth hormone a hormone that is secreted by the anterior lobe of the pituitary gland and that regulates the growth of most tissues (abbreviation, GH)

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growth hormone

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growth rate an expression of the increase in the size of an organism or population over a given period of time

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growth rate

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growth regulator an organic compound that stimulates or inhibits physiological processes in plants

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growth regulator

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guanine one of the four bases that combine with sugar and phosphate to form a nucleotide subunit of DNA; guanine pairs with cytosine

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guanine

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guard cell one of a pair of specialized cells that border a stoma and regulate gas exchange

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guard cell

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Gulf Stream the swift, deep, and warm Atlantic current that flows along the eastern coast of the United States toward the northeast

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Gulf Stream

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gut the digestive tract

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gut

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gymnosperm a woody, vascular seed plant whose seeds are not enclosed by an ovary or fruit

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gymnosperm

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gyre a huge circle of moving ocean water found above and below the equator

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gyre