Abiotic

A physical or chemical factor affecting an ecosystem e.g. light intensity or temperature.

Absorption

The movement of digested food molecules through the wall of the intestine into the blood.

Accommodation

Adjustments made by the eye to produce a clear image on the retina.

Accuracy

How close the result is to the 'true value'.

Acid rain

Rain that is more acidic than normal because various gases (such as sulphur dioxide) have dissolved in it.

Active

A process which requires energy to occur.

Active site

The part of an enzyme into which a substrate fits during a reaction.

Active transport

Active movement of molecules from an area of low concentration to an area of high concentration, against a concentration gradient, using carrier proteins.

Adaptation

A feature of an organism that is well suited to its function and helps the organism survive.

Adenine

One of the nitrogenous bases found in DNA and RNA. Pairs with thymine in DNA and uracil in RNA.

ADH

A hormone produced by the pituitary gland which is involved in control of water levels in the body, makes the collecting duct more permeable to water.

Adrenaline

A hormone produced by the adrenal gland in response to stressful situations. Affects the circulatory, respiratory and digestive systems.

Aerobic respiration

Respiration that requires the presence of oxygen.

Algal bloom

The rapid growth of algae resulting from an increased nutrient supply.

Allele

One of the alternative forms of a gene.

Alveoli

The air sacs in the lungs where gas exchange takes place, site of gas exchange in the lungs.

Amino acid

The monomer from which proteins are made, contain carbon, hydrogen, oxygen and nitrogen (some have sulphur).

Amnion

Membrane enclosing the embryo during pregnancy.

Amniotic fluid

Fluid secreted by the amnion, which supports and protects the developing embryo.

Amylase

An enzyme that digests starch into maltose. Produced in the mouth and pancreas.

Anaerobic respiration

Respiration that takes place in the absence of oxygen.

Animal

Multicellular organisms that have no cell walls, form zygotes after fertilisation and ingest their food.

Anomaly

A reading which falls outside the normal, expected, range of measurements.

Anther

The part of the stamen in which pollen is formed and from which it is released.

Antibody

Proteins secreted by lymphocytes in response to pathogens, attach to pathogens and destroy them.

Anticodon

A group of three bases on a tRNA molecule that are complementary to the codon on the mRNA.

Antigen

A chemical 'marker' on the surface of a cell that identifies it.

Anus

The passage through which faeces are egested.

Aorta

The artery which leaves the left ventricle of the heart.

Arteriole

A small artery.

Artery

A blood vessel which takes blood away from the heart towards the capillaries.

Asexual reproduction

Reproduction which does not involve the fusion of gametes, produces genetically identical offspring.

ATP

A chemical produced in respiration and used in processes that require energy.

Atrium

A chamber in the heart which receives blood returning to the heart, smaller than a ventricle.

Auxin

Plant growth factor involved in the control of cell elongation.

Axon

A long projection in a neurone that carries nerve impulses away from the cell body.

Baby

A child which has just been born.

Bacteria

Single celled organisms that do not contain any membrane bound organelles and possess circular DNA in chromosomes and plasmids.

Bacterial chromosome

The large loop of DNA found within bacterial cells.

Bacteriophage

A virus that infects bacteria that can be used as a vector in genetic engineering.

Balanced diet

A diet that contains all the basic nutrients in the proportions necessary to maintain health.

Benedict's reagent

Used to test for sugar in the Benedict's test.

Bicuspid valve

Valve in the heart between the left atrium and ventricle.

Bile

Produced by the liver and stored in the gall bladder. Bile emulsifies fats to increase the surface area for lipase to act on.

Bioaccumulation

Build up of pollutants in an organism.

Biodiversity

The amount of variation shown by organisms in an ecosystem; it takes into account the number of species and abundance (number) of each species.

Biological control

The use of natural predators or parasites to control pest populations.

Biomagnification

The increase in concentration of bioaccumulated substances (e.g. pollutants) along a food chain.

Biomass

The measure of mass of living material present of a species, measured in g per meter squared.

Biotic factor

A biological factor affecting an ecosystem e.g. predation.

Bladder

The organ where urine is stored before being lost through the urethra.

Blind spot

Area of the retina where the optic nerve leaves the eye.

BOD

Biological Oxygen Demand; the amount of oxygen in water used up by organisms, measured in mg per litre.

Bowman's capsule

The first part of the nephron, site of ultrafiltration.

Brain

The organ which coordinates the activities of the nervous system. Part of the CNS.

Bronchiole

One of the smaller airways of the respiratory system, connects the main airways (bronchi) to the alveoli.

Bronchus

One of the main airways of the respiratory system, connects the trachea to the bronchioles.

Calcium

An important mineral ion used in the formation of bones and teeth. Found in dairy products, fish and vegetables.

Capillary

The smallest of the blood vessels and the site of substance exchange.

Capsule

An layer found outside the cell wall of in some bacterial species.

Carbohydrase

Enzyme that digests carbohydrates.

Carbohydrate

Starches and sugars; biological molecules containing carbon, hydrogen and oxygen only.

Carbon cycle

The way in which carbon cycles in an ecosystem.

Carbon monoxide

Toxic gas present in car exhaust and cigarette smoke.

Carnivore

An organism which feeds on other organisms.

Carpel

The female reproductive organ of plants, made up of the stigma, style and ovary.

Carrier protein

A protein found in the membrane which helps transport substances into and out of the cell; involved in active transport.

Catalyst

A substance that speeds up the rate of reaction and is not used up in the process.

Cell

The basic unit of living organisms.

Cell division

The process by which one cells forms two daughter cells. Can be by mitosis or meiosis.

Cell membrane

A thin layer that marks the boundary between the cell and the outside. Is selectively permeable and controls what gets into and out of the cell.

Cell sap

Found in the vacuole, a store of sugars, mineral ions, other solutes and water.

Cell wall

A layer outside of the cell membrane that supports cells and helps them to keep their shape. They are made of cellulose in plants, chitin in fungi and a carbohydrate-protein mixture in bacteria.

Cellulose

A carbohydrate found in plants, the main component of cell walls in plants.

CHD

Disease caused by blockage of the coronary arteries due to build up of fatty material, which can lead to a heart attack.

Chitin

Chemical that makes up the cell wall of fungi.

Chlorophyll

A green, magnesium containing pigment involved in photosynthesis.

Chloroplast

The site of photosynthesis in plant cells, contains the pigment chlorophyll.

Cholesterol

Lipid substance present in the blood that can lead to CHD.

Chromosome

A threadlike structure in the nucleus formed of DNA.

Cilia

Microscopic hair-like projections on the surface of cells lining the trachea and bronchi that can move mucus and trapped particles out of the lungs.

Ciliary muscles

Muscles in the eye responsible for altering the shape of the lens.

Clone

Organisms which are genetically identical to each other.