Science / Biology Glossary

Huntington Disease: A progressive and fatal disorder of the nervous system that develops between the ages of 30 and 50 years; caused by an expansion of a trinucleotide repeat and inherited as a dominant trait.

Hydrogen Bond: A weak bond between two atoms (one of which is hydrogen) with partial but opposite electrical charges.

Hydrophilic: Water-loving. Term applied to polar molecules that can form a hydrogen bond with water.

Hydrophobic: Water-fearing.Term applied to nonpolar molecules that cannot bond with water.

Hydrophytic Leaves: The leaves of plants that grow in water or under conditions of abundant moisture.

Hydrosphere: The part of the physical environment that consists of all the liquid and solid water at or near the Earths surface.

Hydrostatic Skeleton: Fluid-filled closed chambers that give support and shape to the body in organisms such as jellyfish and earthworms. No to be confused with the water-vascular system of echinoderms.

Hypertension: High blood pressure; blood pressure consistently above 140/90.

Hypertonic: A solution having a high concentration of solute.

Hyphae: The multinucleate or multicellular filaments that make up the mycelium (body) of a fungus (sing.: hypha).

Hypothalamus: A region in the brain beneath the thalamus; consists of many aggregations of nerve cells and controls a variety of autonomic functions aimed at maintaining homeostasis.

Hypothesis: An idea that can be experimentally tested; an idea with the lowest level of confidence.

Hypotonic: A solution having a low concentration of solute.

Ice Age: Interval of geologic time between 2 million and 10,000 years ago during which the northern hemisphere experienced several episodes of continental glacial advance and retreat along with a cli . . . View Full Definition

Ileum: The third and last section of the small intestine.

Immovable Joint: A joint in which the bones interlock and are held together by fibers or bony processes that prevent the joint from moving; e.g., the bones of the cranium.

Immune System: One of the eleven major body organ systems in vertebrates; defends the internal environment against invading microorganisms and viruses and provides defense against the growth of cancer cells.

Immunoglobulins: The five classes of protein to which antibodies belong (IgD, IgM, IgG, IgA, IgE).

Implantation: The process in which the blastocyst embeds in the endometrium.

Incomplete Dominance: A type of inheritance in which the heterozygote has a phenotype intermediate to those of the homozygous parents.

Incomplete Flower: Condition in which one or more typical flower parts are absent. Example: grass flowers such as corn tassels which are male.

Incus: One of the three bones comprising the middle ear of mammals.

Inflammation: A reaction to the invasion of microorganisms through the skin or through the epithelial layers of the respiratory, digestive, or urinary system; characterized by four signs: redness, swellin . . . View Full Definition

Inflammatory Response: The bodys reaction to invading infectious microorganisms; includes an increase in blood fiow to the affected area, the release of chemicals that draw white blood cells, an increased fiow of . . . View Full Definition

Ingestive Feeders: Animals that ingest food through a mouth.

Page: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53