Science / Biology Glossary

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 no . . . View Full Definition

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 p . . . View Full Definition

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 . . . View Full Definition

Guanine: One of the nitrogenous bases in nucleic acids, guanine is one of the two purine bases.

Guard Cells: Specialized epidermal cells that flank stomates and whose opening and closing regulates gas exchange and water loss.

Gymnosperms: Flowerless, seed-bearing land plants; the first 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.

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 skins surface to the hair bulb.

Hair Shaft: The portion of a hair that extends above the skins 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.

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