Biology Terms +

(a glossary of biological terms about living creatures including plants and all kinds of animal species and organisms)

ABO blood typing
A method of using the presence of proteins "A", "B", or both at the surface of red blood cells to characterize an individual's blood type; while "O" signifies the absence of both of the proteins.
abortion
Premature, spontaneous, or induced expulsion of the embryo or fetus from the uterus.

Spontaneous abortion is also called miscarriage.

absorption
The uptake of water and solutes from the environment by a cell or a multi-celled organism; that is, the movement of nutrients, fluid, and ions across the gut lining and into the internal environment.
accessory pigment
Any of a variety of light trapping pigments which extend the range of wavelengths for photosynthesis beyond those absorbed by chlorophylls (green coloring matter of leaves and plants which are essential to the production of carbohydrates by photosynthesis).
acid rain
Wet acid deposition or the falling of rain (or snow) rich in sulfur and nitrogen oxides.
acidity
1. A reference to a solution which consists of an excess of hydrogen ions relative to hydroxyl ions (having one oxygen and one hydrogen atom).
2. The concentration of acid in a substance.
acoelomate
The absence of a fluid-filled cavity between the gut and the body wall.
acoustical signal
Sounds used as a form of intraspecific communication; that is, being within or occurring among the members of the same species.
actin
1. Cytoskeletal protein (microtubules, microfilaments, and larger filaments, functioning as a structural support and transport mechanism); a subunit of microfilaments or the smallest of the cytoskeletal filaments.
2. A protein which is abundantly present in many cells; especially, muscle cells, that significantly contributes to the cell's structure and motility.

Actin can very quickly assemble into long polymer rods called microfilaments. These microfilaments have a variety of roles in that they form part of the cell's cytoskeleton, they interact with myosin to permit movement of the cell, and they pinch the cell into two during cell division.

In muscle contraction, filaments of actin and myosin alternately unlink and chemically link in a sliding action.

The energy for this reaction is supplied by adenosine triphosphate; which is, the major energy source within a cell to drive a number of biological processes; such as, photosynthesis, muscle contraction, and the synthesis of proteins.

action potential
The change in the potential difference (voltage) across the membrane of a nerve cell when an impulse passes along it.

A change in potential (from about -60 to +45 millivolts) accompanies the passage of sodium and potassium ions across the membrane.

action potentiality
1. An abrupt, brief reversal in the resting membrane potential of a neuron and other excitable cells.
2. The local voltage change across a cell wall as a nerve impulse is transmitted.
3. A momentary change in electrical potential on the surface of a nerve or muscle cell that takes place when it is stimulated; especially, by the transmission of a nerve impulse.
activation energy
For each type of reaction, the minimum amount of collision energy that will drive reactant molecules to an activated condition, from which the reaction will proceed spontaneously.
adaptive trait
Any aspect of form, function, or behavior which helps the individual organism survive and reproduce under prevailing conditions.
adaptive zone
A way of life available for organisms which are physically, ecologically, and evolutionarily equipped to live it; such as, "catching insects in the air at night".
adipose tissue
1. A connective tissue having an abundance of fat-storing cells and blood vessels for transporting fats.
2. Connective tissue that serves as an energy reserve and also pads some organs.

It is normally called "fat tissue" and consists of large spherical cells filled with fat. Major layers are in the inner layer of the skin and around the kidneys and heart.

Also check out the Index for other Scientific and Technological Topics.