Glossary  (Page 9/18)

Hermaphrodite When one organism has both male and female sex organs eg earthworms and most flowering plants

Heterotrophic Uses complex organic foods to get its nutrients (compare with autotrophic)

Hexose A sugar which has 6 carbon atoms in its molecule

Histamine A chemical given out by mast cells during the allergic response; it causes dilation of blood vessels

Histone A special protein that attaches to DNA molecules and is used to package the DNA; DNA plus histone makes chromatin

Histogram Graph using columns that is used when the independent variable data is grouped according to classes

Homeostasis Maintaining a constant internal environment

Homeothermic Having a constant body temperature which is maintained by homeostasis

Hominid The group of primates that use two legs for walking; only Homo sapiens still lives, the other species are extinct

Homologous Structures that look similar to each other or have the same origin

Hormone A chemical messenger substance made in ductless glands and carried in the blood to act somewhere else

Humid The air contains a lot of water vapour.

Hydathode A gland on the surface of a leaf that forms water drops for guttation

Hydrogen bond A very weak chemical bond between the negatively charged part of one molecule and the positively charged part of another molecule

Hydrolysis When a large molecule is split into two smaller parts by adding a water molecule to it (compare with Condensation)

Hydrostatic The pressure caused by a liquid such as water when at rest

Hypertonic Having a lower solute potential than the reference solution

Hypophysis Another name for the pituitary gland in the middle of the head, below the brain

Hypothalamus The floor of the thalamus (front brain) which links the nerve and hormone systems for better body co-ordination

Hypothesis Statement that is a possible explanation which can be tested by experiment to find out if it is true or not

Hypotonic Having a higher solute potential than the reference solution (compare with

Hypertonic)

Ileum The longest part of the small intestine. It is about 4 m long in humans. Most

absorption happens in it

Impermeable Substances are not able to pass through it

Implantatio n The process in which a new embryo settles onto the wall of the uterus

Impotent In males, unable to have sexual relations because the penis will not erect

Incomplete dominance The blending of the expression of two alleles because neither of the pair is dominant to the other

Impulse In life sciences, the message that passes along a nerve

Incisor The front chisel shaped teeth

Indicator A substance which changes colour to show that another substance is present eg. litmus goes red if acid present

Indigenous Native to the place and not introduced there by people

Infectious A disease caused by a living organism that can pass from one person to another

Inflammation A redness or swelling of tissue in response to an injury

Ingestion Taking in food at the mouth

Inhale To breathe in

Inhibit To slow down or reduce the effect

Inorganic Substance that is not organic, it usually does not have large molecules and usually does not have carbon.