- Habitat
- environment in which a plant or animal lives; its home
- Halophytes
- plants that can grow in soils with a high salt content
- Haustoria
- slender portion of leaf or stem modified for twinning; a tendril
- Hectocotylus
- one of arms of most male cephalopods such as an octopus that is modified to transfer spermatophores from a male to a reproductive female
- Hemoglobin
- iron-containing pigment in red blood cells that conveys oxygen to tissues
- Herbivore
- animal adapted to subsist solely or mainly on plant food
- Home range
- area in which an animal lives
- Homoeothermic
- warm-blooded; body temperature controlled internally and maintained at a constant level; endothermic
- Hydra
- small jelly animals with a polyp form that are found only in fresh water; colonies are shaped like feathers or very small trees
- Hydrodynamics
- branch of physics that studies fluids in motion and the forces that affect motion
- Hydroid
- colony of polyps growing on a common stalk; found only in salt water; form colonies shaped like feathers or very small areas
- Hydromedusae
- small jellies usually less than 25mm (1 in)
- Hydrophone
- microphone submerged in water
- Hydrozoan
- class of Phylum Cnideria that includes hydroids, hydra, and the Portuguese man-of-war
