ORT Biology key terms

A thin double layer of lipid molecules studded with proteins that surrounds every cell and controls which substances enter or leave it.

The random spreading of particles from a region of higher concentration to one of lower concentration, driven by their own kinetic energy and needing no energy input.

The movement of water across a partially permeable membrane from a dilute solution to a more concentrated one, tending to equalise solute concentrations on the two sides.

A protein that speeds up a specific chemical reaction by lowering its activation energy, without being used up itself; its shape determines which substrate it acts on.

The small region of an enzyme molecule, formed by its folded shape, where the substrate binds and the reaction is catalysed.

Loss of a protein's functional three-dimensional shape caused by heat, extremes of pH or chemicals, so that enzymes stop working and structures break down.

The release of energy from glucose using oxygen, producing carbon dioxide and water in mitochondria and yielding far more ATP per glucose than anaerobic pathways.

Adenosine triphosphate, the small molecule that stores and transfers chemical energy in cells; releasing its terminal phosphate group powers many cellular processes.

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

The green pigment inside chloroplasts that absorbs mainly red and blue light and passes the captured energy into the reactions of photosynthesis.

A membrane-bound organelle with folded inner membranes where the later stages of aerobic respiration take place, supplying most of a cell's ATP.

A length of DNA that carries the instructions for making a particular protein or functional RNA, and is inherited from parent to offspring.

One of the alternative versions of a gene that can occupy the same position on a chromosome, such as the versions producing brown or blue eye colour.

The combination of alleles an organism carries for a particular gene, for example homozygous dominant, heterozygous or homozygous recessive.

The observable characteristics of an organism, which result from its genotype interacting with the environment it has experienced.

A long thread-like structure of DNA wrapped around proteins, found in the nucleus of eukaryotic cells and carrying genes in a fixed linear order.

A type of cell division that halves the chromosome number and shuffles alleles, producing genetically varied gametes for sexual reproduction.

A change in the base sequence of DNA, which may alter the protein produced and so create a new allele that can be inherited.

The maintenance of a stable internal environment, such as constant body temperature or blood glucose, despite changes in the surroundings.

A control mechanism in which a change away from the normal level triggers a response that reverses the change and brings conditions back towards the set point.

A chemical messenger released by an endocrine gland into the blood, which travels to target organs and alters their activity.

One of the tiny air sacs in the lungs whose thin, moist, richly supplied walls allow efficient exchange of oxygen and carbon dioxide with the blood.

The microscopic filtering unit of a kidney, which removes wastes from the blood and reabsorbs useful substances such as glucose and water.

A sequence showing the feeding relationships in a community, in which each organism eats the one before it and is eaten by the one after it.

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

A feeding position within a food chain or web, such as primary producer, primary consumer or secondary consumer, each step representing a transfer of energy.

An organism such as a bacterium or fungus that breaks down dead material and wastes, releasing nutrients back into the soil for reuse.

A community of living organisms together with the non-living parts of their environment, such as soil, water and climate, interacting as a unit.

The process by which individuals with inherited features better suited to their environment survive and reproduce more, so those features become more common over generations.

An inherited feature of a population that improves its chance of survival and reproduction in a particular habitat, such as thick fur in cold regions.

A group of organisms with similar characteristics that can breed together to produce fertile offspring, but cannot do so with other such groups.

The loss of water vapour from the leaves of a plant, mainly through stomata, which pulls water up the stem and cools the plant.

Tiny pores in the surface of a leaf, each bounded by guard cells, through which carbon dioxide enters and water vapour and oxygen leave.

Tissue of hollow, dead, lignified cells that carries water and dissolved minerals upward from the roots to the leaves of a plant.

A green organelle in plant cells that contains chlorophyll and is the site where photosynthesis makes glucose from carbon dioxide and water.

A sex cell such as a sperm, egg or pollen nucleus, which carries half the normal chromosome number and fuses with another at fertilisation.

The fusion of a male and a female gamete to form a single cell with a complete set of chromosomes, the first step in forming a new individual.

The single cell formed when two gametes fuse, which then divides repeatedly by mitosis to develop into an embryo.

Cell division that produces two genetically identical daughter cells, used for growth, repair and asexual reproduction.

A human-directed process in which organisms with desired traits are repeatedly mated so that those traits become more common in later generations.

Deliberately transferring a gene from one organism into another, often of a different species, so the recipient produces a useful new product.