OGE Biology key terms

The set of all chemical reactions in a living organism that convert nutrients into energy and building materials, and break down waste products. It includes both building-up (anabolism) and breaking-down (catabolism) processes.

The ability of a living organism to keep its internal conditions, such as temperature, water content and blood chemistry, within narrow limits despite changes in the surroundings.

The general ability of living things to respond to stimuli such as light, heat, chemicals or touch. In animals it often takes the form of rapid nervous reactions, while in plants it appears as growth movements.

The process by which organisms produce new individuals of their own kind, passing on genetic material. It may be asexual, giving genetically identical offspring, or sexual, mixing genes from two parents.

A testable, tentative explanation for an observed biological phenomenon, stated so that it can be checked by experiment or further observation. It is accepted or rejected on the basis of evidence.

A controlled procedure in which one factor is deliberately changed while others are kept constant, so that the effect of that factor can be measured and compared with a control group.

The purposeful use of the senses or of instruments such as microscopes to record facts about living things without altering them. It supplies the raw data from which questions and hypotheses are formed.

The smallest structural and functional unit of every living organism, bounded by a membrane and containing cytoplasm and genetic material. Some organisms consist of a single cell, others of many cooperating cells.

The thin, flexible outer layer of a cell made of lipids and proteins. It controls which substances enter and leave the cell and separates its contents from the surrounding environment.

The jelly-like substance filling the inside of a cell, outside the nucleus. It contains water, salts, organic molecules and the organelles, and is where many chemical reactions of the cell take place.

The membrane-bound organelle of eukaryotic cells that stores the chromosomes and directs the cell's activities by controlling which proteins are made.

A specialized structure inside a cell, such as a mitochondrion, chloroplast or ribosome, that performs a particular job for the cell. Most organelles are enclosed by their own membranes.

An organelle found in eukaryotic cells where aerobic respiration takes place, releasing energy from glucose. Cells with high energy demands, such as muscle cells, contain many of them.

The green organelle of plant cells containing chlorophyll, where photosynthesis traps light energy and uses it to build sugars from carbon dioxide and water.

The process in green plants and some other organisms that uses light energy to combine carbon dioxide and water into glucose, releasing oxygen as a by-product.

The release of energy from organic molecules such as glucose inside cells. Aerobic respiration uses oxygen and yields more energy; anaerobic respiration occurs without oxygen and yields less.

A protein that speeds up a specific chemical reaction in a living organism without being used up itself. Each enzyme works best at a particular temperature and pH.

A type of cell division producing two daughter cells with the same number of chromosomes as the parent cell. It is used for growth, repair and asexual reproduction.

A type of cell division that halves the chromosome number and produces four genetically different cells, called gametes. It takes place in the sex organs and creates variation in offspring.

A thread-like structure in the nucleus made of DNA and protein that carries genes. Human body cells contain 46 chromosomes, arranged in 23 pairs.

Single-celled organisms without a true nucleus, whose genetic material lies free in the cytoplasm. They reproduce by simple division and may be helpful, harmless or disease-causing.

An organism such as a mould, yeast or mushroom that has cells with nuclei but no chlorophyll, so it feeds by absorbing nutrients from other matter. Many fungi are decomposers.

Simple plant-like organisms, mostly living in water, that contain chlorophyll and make their own food by photosynthesis. They range from single cells to large seaweeds.

An organism, usually a fungus or bacterium, that feeds on dead organic matter, breaking it down and absorbing the nutrients. Saprophytes play a key role in recycling matter in ecosystems.

An animal with an internal skeleton and a backbone protecting a nerve cord, such as fish, amphibians, reptiles, birds and mammals. Vertebrates form one major group of the animal kingdom.

A warm-blooded vertebrate that has hair, feeds its young on milk from mammary glands, and usually gives birth to live young. Mammals breathe with lungs.

The breakdown of large food molecules into smaller ones that can be absorbed into the blood. It happens mechanically by chewing and chemically by enzymes in the digestive tract.

The movement of digested nutrients, water and minerals from the digestive tract into the blood or lymph. Most absorption occurs through the folded inner surface of the small intestine.

A fast, automatic response to a stimulus that does not require conscious thought, such as blinking or pulling the hand from a hot object. Reflexes protect the body from harm.

A nerve cell specialized for carrying electrical impulses. It has a cell body, branching dendrites that receive signals, and a long axon that transmits signals to other cells.

The body's ability to resist a particular infection, either because it has produced antibodies after exposure or vaccination, or because it has received ready-made antibodies.

The introduction of weakened or harmless forms of a pathogen into the body so that it produces protective antibodies and memory cells. This creates immunity without causing the disease.

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

A self-regulating natural community of plants, animals, fungi and microbes living in a particular area with a uniform set of environmental conditions, linked by flows of matter and energy.

A sequence of organisms in which each is eaten by the next, showing how energy and matter pass from producers to consumers and finally to decomposers.

An organism, usually a green plant or alga, that makes its own organic food from sunlight by photosynthesis. Producers form the base of every food chain.

An organism such as a bacterium or fungus that breaks down dead bodies and waste into simple substances, returning nutrients to the soil and water for reuse.

A feature or behaviour of an organism that improves its chances of surviving and reproducing in its particular environment, usually shaped over many generations by natural selection.

The process by which individuals with inherited features that suit their environment survive and leave more offspring, so those features become more common in later generations.

The gradual change in the inherited characteristics of populations over many generations, which can lead to new species and to the diversity of life on Earth.