BGCSE Biology 0572 key terms

The thin, partially permeable layer surrounding a cell that controls which substances enter and leave, holding the cell contents together and allowing gases, water and dissolved food to pass through selectively.

The smallest living unit of an organism, containing cytoplasm and genetic material and surrounded by a membrane; organisms may consist of one cell or many specialised cells working together.

The structure inside most cells that contains the chromosomes, which carry genetic information in DNA and control the activities and division of the cell.

A green structure found in plant cells that contains chlorophyll and absorbs light energy so that glucose can be made from carbon dioxide and water during photosynthesis.

The net movement of particles from a region of higher concentration to a region of lower concentration, caused by random motion, until the particles are evenly spread.

The movement of water molecules through a partially permeable membrane from a dilute solution to a more concentrated solution, or from pure water into a solution.

The movement of dissolved substances across a membrane from a lower to a higher concentration, using energy released by respiration rather than relying on random particle motion.

A protein that speeds up a specific chemical reaction in living things without being used up, by joining or splitting particular substrate molecules at its active site.

The breakdown of large, insoluble food molecules into smaller, soluble molecules that can be absorbed through the wall of the small intestine into the blood.

A finger-like fold of the lining of the small intestine that greatly increases the surface area for absorbing digested food, and contains a rich blood supply.

The process by which digested food molecules, water, minerals and vitamins pass from the inside of the intestine into the blood or lymph vessels.

A green liquid made in the liver, stored in the gall bladder and released into the small intestine, where it emulsifies fats and neutralises acid from the stomach.

The chemical reactions inside living cells in which glucose is broken down to release energy, with oxygen (aerobic) or without oxygen (anaerobic), producing carbon dioxide and water in aerobic conditions.

The release of energy from glucose in cells without using oxygen, producing lactic acid in human muscle cells or ethanol and carbon dioxide in yeast.

The breakdown of sugar by microorganisms such as yeast without oxygen, producing ethanol and carbon dioxide; used in bread making and in brewing.

A tiny air sac in the lungs where gas exchange happens; its thin, moist wall and dense capillary network allow oxygen to diffuse into the blood and carbon dioxide to diffuse out.

A blood vessel that carries blood away from the heart under high pressure; its thick, elastic, muscular wall helps it stretch and recoil with each heartbeat.

A blood vessel that carries blood towards the heart at low pressure, has a thinner wall than an artery and contains valves that prevent the blood from flowing backwards.

A very narrow blood vessel with a wall one cell thick, linking arteries to veins and allowing substances to diffuse easily between the blood and surrounding tissues.

The control of conditions inside the body, such as temperature, blood glucose and water content, so that they stay close to the levels needed for cells to work properly.

The control of the water and salt content of body fluids by the kidneys, which adjust how much water is reabsorbed into the blood and how much is lost in urine.

A control mechanism in which a change from the normal level triggers a response that reverses the change, bringing the condition back towards its set point.

A rapid, automatic response to a stimulus that does not involve conscious thought, travelling along a pathway from receptor through a relay neurone to an effector.

A nerve cell specialised for carrying electrical impulses quickly, having a long fibre and many branched endings that connect with other cells.

The small gap between two neurones, or between a neurone and a muscle, across which a chemical transmitter diffuses so the impulse can be passed on.

A chemical messenger made by an endocrine gland and carried in the blood to a target organ, where it alters the activity of particular cells.

A specialised cell or nerve ending that detects a particular stimulus, such as light, temperature or pressure, and starts an impulse in a sensory neurone.

Cell division that produces four genetically different gametes, each with half the normal number of chromosomes, so that fertilisation restores the full number.

Cell division producing two genetically identical daughter cells with the same chromosome number as the parent, used for growth, repair and asexual reproduction.

A permanent increase in size and mass of an organism, brought about by cell division and by cells becoming larger or more specialised.

One of the different forms of a gene that can occupy the same position on a chromosome and control the same characteristic, for example the alleles for tall and short stems.

The combination of alleles an organism carries for a particular characteristic, which may be homozygous (two identical alleles) or heterozygous (two different alleles).

The visible or measurable characteristics of an organism, resulting from its genotype interacting with the environment in which it grows.

Describing an allele that produces its effect in the phenotype even when only one copy is present, masking the effect of a recessive allele.

A sequence showing the transfer of energy from one organism to the next, beginning with a producer and continuing through consumers, with arrows showing direction of energy flow.

An organism, usually a green plant or alga, that makes its own organic food by photosynthesis and so forms the starting point of a food chain.

An organism such as a bacterium or fungus that breaks down dead organisms and waste materials, releasing minerals back into the soil for plants to use.

The process in green plants in which light energy is used to combine carbon dioxide and water into glucose, releasing oxygen as a by-product.

The grouping of organisms into categories based on shared features, such as cell type, body plan and method of feeding, to show their relationships.

A group of organisms with very similar features that can breed together to produce fertile offspring, and which do not normally breed with other groups.

A factor in an experiment that can change; the independent variable is deliberately altered, the dependent variable is measured, and others must be controlled.

The extent to which repeated measurements or repeated experiments give consistent results, improved by taking repeats, using larger samples and averaging the data.

An investigation in which only the independent variable is changed while all other relevant factors are kept the same, so that any effect can be attributed to that variable.