AS Biology (A words)

Abundance

The frequency of occurrence of plants in a sampled area, such as a quadrat

Activation Energy

The level of energy required to enable a reaction to take place. Enzymes reduce the amount of energy required to allow a reaction to proceed

Active immunity

Immunity that is acquired by activation of immune system

Active site

The area on an enzyme molecule to which the substrate binds

Active transport

Movement of substances across membranes against their concentration gradient, requiring the use of energy in the form of ATP. Active transport usually involves the use of transport proteins

Adaption

Feature of a living organism that increases its chances of survival, for example thick fur on an animal that lives in a cold habitat

Adenine

A nitrogen-containing organic base found in nucleic acids. It pairs with thymine in DNA and with uracil in RNA.

Adhesion

Force of attraction between molecules of two difference substances

Adipose

Describes tissue consisting of cells that store fat/lipid

Affinity

An attractive force between substances of particles

Allele

A version of a gene

Allopatric

Speciation due to organisms of a species being separated by geographical barriers so that over time members of the two populations become so difference that they cannot interbreed and are considered to be two difference species

Alveoli

Small air sacs in the lungs

Amino acid

An organic compound that contains both an amino group (-NH2) and a carboxyl group (-COOH). Amino acids are the monomers of protein molecules.

Amylase

An enzyme that catalyses the hydrolysis of starch to maltrose

Amylose

Part of a starch molecule, consisting of many thousands of glucose residues bonded together

Anaphase

In mitosis, the stage when the newly separated chromatids are pulled towards opposite poles of the nuclear spindles

Anomalous

Describes a result/data point that does not appear to fit the pattern of the other results. It may be assumed to be anomalous if the experimenter has made an error or if the apparatus used is not suitable for the measurements being taken

Antibiotics

Molecules produced by microorganisms that kill or limit the growth of other microorganisms

Antibodies

Protein molecules released by the immune system in response to an antigen, which are capable of neutralising the effects of the antigen.

Antigen

A foreign molecule (which may be protein or glycoprotein) that can provoke an immune response. Organisms have antigens on their plasma (cell surface) membranes.

Antigen-presenting cell

A macrophage that has ingested a pathogen and displays the pathogen’s antigens on its cell surface membrane.

Apoplast pathway

The route taken by water between the cells or through the cell walls in a plant.

Arteriosclerosis

Hardening of the artery walls and loss of elasticity caused by atherosclerosis or by deposition of calcium.

Artificial immunity

Immunity acquired as a result of deliberate exposure to antigens or by the injection of antibodies.

Artificial selection

Also called selective breeding – the process of improving a variety of crop plant or domesticated animal by breeding from selected individuals with desired characteristics.

Asexual reproduction

The production of genetically identical new organisms by a single ‘parent’ organism.

Alpha - helix

A protein structure - a right handed spiral held in place by hydrogen bonds between adjacent C=O and NH groups