Alevel Biology key terms

Abiotic

An ecological factor that makes up part of the non-biological environment of an organism, e.g. temperature, pH, rainfall and humidity

Acetylcholine

A group of chemicals called neurotransmitters, released by neurones. It diffuses across the synapse between adjacent neurones and passes an impulse from one neurone to the next

Action Potential

Change that occurs in the electrical charge across the membrane of an axon when it is stimulated and a nerve impulse passes

Actin

Filamentous protein which is involved in contraction within cells, specifically muscle cells.

Activation Energy

Energy required to bring about a reaction

Active Immunity

Resistance to disease resulting from the activities of an individual's own immune system whereby an antigen induces plasma cells to produce antibodies

Active Site

A group of amino acids that makes up the region of an enzyme into which the substrate fits in order to catalyse a reaction

Active Transport

Movement of a substance from a region where it is in a low concentration to a region where it is in a high concentration. The process requires the expenditure of metabolic energy

Adenosine Triphosphate (ATP)

An activated nucleotide found in all living cells that acts as an energy carrier. The hydrolysis of ATP leads to the formation of ADP and inorganic phosphate, with the release of energy.

Adrenaline

A hormone produced by the adrenal glands in times of stress that prepares the body for an emergency

Aerobic

Connected with the presence of free oxygen. Aerobic respiration requires free oxygen to release energy from glucose

Alelle

One of a number of alternative forms of a gene.

For example, the gene for the shape of pea seeds has two alleles: one for 'round' and one for 'wrinkled'

Allergen

A normally harmless substance that causes the immune system to produce an immune response.

Allergy

The response of the immune system to an allergen

Examples include hay fever and asthma

Anaerobic

Connected with the absence of oxygen. Anaerobic respiration releases energy from glucose or other foods without the presence of oxygen

Antibiotic

A substance produced by living organisms that can destroy or inhibit the growth of microorganisms

Antibiotic Resistance

The development in microorganisms of mechanisms that prevent antibiotics from killing them

Antibody

A protein produced by lymphocytes in response to the presence of the appropriate antigen

Anticodon

A sequence of three adjacent nucleotides on a molecule of transfer RNA that is complementary to a particular codon on a messenger RNA molecule

Antidiuretic Hormone (ADH)

A hormone produced by the hypothalamus that passes to the posterior pituitary gland from where it is secreted. Reduces the volume of water in urine by increasing water reabsorption in the kidneys

Antigen

A molecule that triggers an immune response by lymphocytes

Antioxidant

Chemical which reduces or prevents oxidation. Often used as an additive to prolong the shelf-life of certain foods

Apoplastic Pathway

Route through the cell walls and intercellular spaces of plants by which water and dissolved substances are transported

Artificial Selection

Breeding of organisms by human selection of parents/gametes in order to perpetuate certain characteristics and/or to eliminate others

Asthma

A chronic illness in which there is resistance to air flow to the alveoli of the lungs as a result of the airways becoming inflamed due to an allergic response to an allergen

Atheroma

Fatty deposits in the walls of arteries, often associated with high cholesterol levels in the blood

Autonomic Nervous System

Part of the nervous system that controls the muscles and glands but is not under voluntary control

Autosomes

A chromosome which is not a sex chromosome

Axon

A process extending from a neurone that conducts action potentials away from the cell body

B Cell (B Lymphocyte)

Type of white blood cell that is produced and matures within the bone marrow. B lymphocytes produce antibodies as part of their role in immunity

Benedict's Test

A simple biochemical reaction to detect the presence of reducing sugars

Biodiversity

The range and variety of genes, species and habitats within a particular region

Biomass

The total mass of living material, normally measured in a specific area over a given period of time

Biotic

An ecological factor that makes up part of the living environment of an organism. e.g. food availability, competition and predation

Biosensor

A device that uses biological molecules to measure the level of certain chemicals

Biuret Test

A simple biochemical reaction to detect the presence of protein

Body Mass Index (BMI)

A person's body mass in kilograms divided by the square of their height in metres

Cancer

A disease, resulting from cells that break away from an original tumour to form secondary tumours elsewhere in the body

Carcinogen

A chemical, a form of radiation, or other agent that causes cancer

Cardiac Cycle

A continuous series of events which make up a single heart beat

Cardiac Output

The total volume of blood that the heart can pump each minute (stroke volume x heart rate)

Carrier Molecule (Carrier Protein)

A protein on the surface of a cell that helps to transport molecules and ions across plasma membranes

Casparian Strip

A distinctive band of suberin around the endodermal cells of a plant root that

prevents water passing into xylem via the cell walls. The water is forced through the living part (protoplast) of the endodermal cells

Centrifugation

Process of separating out particles of different sizes and densities by spinning them at high speed in a centrifuge

Cholesterol

Lipid that is an important component of cell-surface membranes. Excess in blood can lead to atheroma

Chromatid

One of the two strands of a chromosome that are joined together by a single centromere prior to cell division

Chromatin

The material that makes up chromosomes. It consists of DNA and the protein histone

Chromosome

A thread-like structure made of protein and DNA by which hereditary information is physically passed from one generation to the next

Climax Community

The organisms that make up the final stage of ecological succession

Clone

A group of genetically identical cells or organisms formed from a single parent as the result of asexual reproduction or by artificial means

Codon

A sequence of three adjacent nucleotides in mRNA that codes for one amino acid

Cohesion

Attraction between molecules of the same type. It is important in the movement of water up a plant

Collagen

Fibrous protein that is the main constituent of connective tissues such as tendons, cartilage and bone

Community

All the living organisms present in an ecosystem at a given time

Complementary DNA

DNA that is made from messenger RNA in a process that is the reverse of

normal transcription

Condensation

Chemical process in which two molecules combine to form a more complex one with the elimination of a simple substance, usually water

Consumer

Any organism that obtains energy by 'eating' another.

Plant eaters = primary consumers, primary consumer eaters = secondary consumers

Continuous Variation

Variation in which organisms do not fall into distinct categories but show

gradations from one extreme to the other

Coronary Arteries

Arteries that supply blood to the cardiac muscle of the heart

Coronary Heart Disease (CHD)

Any condition, for example, atheroma and thrombosis, affecting the coronary arteries that supply heart muscle

Correlation

When a change in one variable is reflected by a change in the second variable

Countercurrent System

A mechanism by which the efficiency of exchange between two substances is increased by having them flowing in opposite directions

Co-transport

The transport of one substance coupled with the transport of another substance across a plasma membrane in the same direction through the same protein carrier

Crossing over

The process whereby a chromatid breaks during meiosis and rejoins to the

chromatid of its homologous chromosome so that their alleles are exchanged

Covalent bond

Type of chemical bond in which two atoms share a pair of electrons, one from each atom

Cuticle

Exposed non-cellular outer layer of certain animals and the leaves of plants.

Waxy, impermeable to water = reduces water loss

Deciduous

Term applied to plants that shed all their leaves together at one season

Denaturation

Permanent changes due to the unravelling of the three-dimensional structure of a protein as a result of factors such as changes in temperature or pH

Depolarisation

Temporary reversal of charges on the cell-surface membrane of a neurone that takes place when a nerve impulse is transmitted

Diastole

The stage in the cardiac cycle when the heart muscle relaxes

Differentiation

The process by which cells become specialised for different functions

Diffusion

The movement of molecules or ions from a region where they are in high concentration to one where their concentration is lower

Dipolar

Having a pair of equal and opposite electrical charges

Diploid

A term applied to cells in which the nucleus contains two sets of chromosomes

Dominant Allele

An allele that is always epressed in the phenotype of an organism, even in the heterozygous

Ecological Niche

Describes how an organism fits into its environment. It describes what a

species is like, where it occurs, how it behaves, its interactions with other species and how it responds to its environment

Ecosystem

All the living and non-living components of a particular area

Effector

An organ that responds to stimulation by a nerve impulse resulting in a

change or response

Electron

Negatively charged subatomic particle that orbits the positively charged nucleus of all atoms

Emphysema

A disease in which the walls of the alveoli break down, reducing the surface area for gaseous exchange, thereby causing breathlessness in the patient

Enzyme

A protein or RNA that acts as a catalyst and so alters the speed of a biochemical reaction

Epidemiology

The study of the spread of disease and the factors that affect this spread

Eukaryotic Cell

Cell that has a membrane-bound nucleus and chromosomes. The cell also possesses a variety of other membranous organelles, such as mitochondria and endoplasmic

reticulum

Exocytosis

The outward bulk transport of materials through the cell-surface membrane

Facilitated diffusion

Diffusion involving the presence of protein carrier molecules to allow the

passive movement of substances across plasma membranes

Gamete

Reproductive cell that fuses with another gamete during fertilisation

Gene

Section of DNA on a chromosome coding for one or more polypeptides

Gene Marker

A section of DNA that is used to indicate the location of a gene or other section of DNA