- Gamete
- mature sperm or egg, capable of fusing during fertilization
- Gametophyte
- gamete-forming phase in alteration of plant generations
- Gastropod
- mollusks of the class Gastropoda, such as snails, slugs, cowries, or limpets, characteristically having a single, usually coiled shell or no shell at all, a ventral muscular foot for locomotion, and eyes and feelers located on a distinct head
- Generic
- relating to or determined by the origin, development, or causal antecedents of something
- Genus
- subdivision of a biological family: biological ranking between family and species
- Gestation
- period during which young are carried in the uterus
- Gill
- aquatic respiratory organ
- Gill net
- a fishing net set vertically in the water so that fish swimming into it are entangled by the gills in its mesh
- Gill raker
- modified dermal denticles that are projections on the inner margin of the gill arches that point forward and upward and act as a sieve by straining water preventing food particles from entering the gills
- GIS
- Geographic Information System: a system of hardware and software used for storage, retrieval, mapping, and analysis of geographic data.
- Gonads
- male and female reproductive organs
- Gonopore
- opening through which eggs or sperm are released, especially in invertebrates
- Gravid
- pregnant; bearing eggs or young
- Grazers
- animals that eat growing herbage, attached algae, or phytoplankton as their principle source of energy
- Gregarious
- tend to live in groups; social
