UCMP Glossary: H

| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |

habit -- The general growth pattern of a plant. A plant's habit may be described as creeping, trees, shrubs, vines, etc.

habitat -- n. An organism's native environment.

halophile -- Organism which lives in areas of high salt concentration. These organisms must have special adaptations to permit them to survive under these conditions.

haploid -- Having a single set of chromosomes in the nucleus of each cell. Mosses, and many protists and fungi, are haploid, as are some insects, bryophytes, and the gametes of all organisms. Contrast with diploid.

haploid life cycle -- Occurs when the only multicellular stage in an organism's life cycle is haploid.

haploid-diploid life cycle -- Occurs when a multicellular diploid phase, or sporophyte, alternates with a multicellular haploid phase, or gametophyte. Only plants and certain algae possess this kind of life cycle, which is also called "alternation of generations".

haptonema -- Peg-like structure unique to the Prymnesiophyta; its function is not known.

head -- That part of the body at the "front" end, where the brain, mouth, and most sensory organs are located.

heart -- Muscular pump which circulates the blood.

hemoglobin -- protein complex found in the blood of most chordates and the roots of certain legumes. It binds oxgen molecules, and in chordates serves as the means by which the oxygen is supplied to the cells of the body.

herb -- Generally any plant which does not produce wood, and is therefore not as large as a tree or shrub, is considered to be an herb.

herbivore -- Literally, an organism that eats plants or other autotrophic organisms. The term is used primarily to describe animals.

heterosporangiate -- Producing two different kinds of sporangia, specifically microsporangia and megasporangia. Compare with heterosporous.

heterosporous -- Producing two different sizes or kinds of spores. These may come from the same or different sporangia, and may produce similar or different gametophytes. Contrast with homosporous, and compare with heterosporangiate.

hierarchy -- A series in which each element is categorized into successive ranks or grades with each level subordinate to the one above.

histones -- proteins attached to the DNA of eukaryotes which allows it to be packaged into chromosomes.

histostructure -- n. The organization and arrangement of tissue (“histo” is from the Greek word for tissue). Since eggshell is a tissue, eggshell histostructure describes the two- and three-dimensional organization of mineral crystals and shell components.

holdfast -- Anchoring base of an alga.

homology -- Two structures are considered homologous when they are inherited from a common ancestor which possessed the structure. This may be difficult to determine when the structure has been modified through descent.

homosporous -- Producing only one size or kind of spore. Contrast with heterosporous.

host -- Organism which serves as the habitat for a parasite, or possibly for a symbiont. A host may provide nutrition to the parasite or symbiont, or simply a place in which to live.

hotspot -- n. A localized, somewhat persistent (tens of millions of years), and relatively fixed zone of mantle melting, inferred from surface volcanic activity. Evidence of a hotspot's existence is left behind as tectonic plates move across it, for example, the Hawaiian Islands.

hydrophilic -- "water loving". Hydrophilic compounds dissolve easily in water, and are usually polar.

hydrophobic -- "water fearing". Hydrophobic compounds do not dissolve easily in water, and are usually non-polar. Oils and other long hydrocarbons are hydrophobic.

hydrothermal vent -- n. A place on the seafloor, generally associated with spreading centers, where warm to super-hot, mineral-rich water is released; may support a diverse community of organisms.

hypersaline -- adj. Extremely salty, having much more salt than normal seawater.

hypha -- n.Threadlike filaments that form the mycelium (body) of a fungus; hyphae- pl.

hypothesis -- A concept or idea that can be falsified by various scientific methods.

Last updated:2009-11-12