Cameroon GCE O-Level Human Biology key terms

A thin, flexible layer surrounding every cell that controls which substances enter and leave. It allows small molecules such as oxygen and water through while restricting others, so it is described as partially permeable.

A rod-shaped structure in the cytoplasm where aerobic respiration takes place. It releases energy from glucose for the cell's activities, so cells that need a lot of energy, such as muscle cells, contain many of them.

Cell division that produces two daughter cells with the same number of chromosomes as the parent cell. It is used for growth, repair of damaged tissues and replacement of worn-out cells in the body.

A type of cell division that halves the chromosome number, producing four genetically different gametes. It occurs in the testes and ovaries and creates variation through the shuffling of chromosomes.

A group of similar cells that work together to carry out one particular function. Examples include muscle tissue, which contracts, and epithelial tissue, which covers and protects body surfaces.

A structure made of several different tissues working together to perform a specific job. The stomach, heart, kidney and lungs are organs, each containing muscle, nervous and other tissues.

A protein that speeds up a chemical reaction in the body without being used up. Each enzyme works on one specific substrate, and its activity is affected by temperature and pH.

The loss of an enzyme's normal shape caused by high temperature or extreme pH. The active site no longer fits the substrate, so the enzyme stops working and the reaction slows or stops.

A green liquid made by the liver, stored in the gall bladder and released into the small intestine. It emulsifies fats into tiny droplets, increasing the surface area for lipase to act on.

Tiny finger-like projections covering the inner wall of the small intestine. They greatly increase the surface area for absorbing digested food and contain blood capillaries to carry nutrients away.

The movement of particles from a region of higher concentration to a region of lower concentration, without needing energy from the cell. It explains how oxygen and carbon dioxide move in and out of cells.

The movement of water molecules through a partially permeable membrane from a dilute solution to a more concentrated one. It explains how water is absorbed in the kidney and how cells keep their water balance.

The pale yellow liquid part of blood, mostly water, which carries dissolved glucose, salts, hormones, urea and carbon dioxide. It also transports blood cells and helps distribute heat around the body.

A disc-shaped blood cell without a nucleus that is packed with haemoglobin. Haemoglobin combines with oxygen in the lungs and releases it in the tissues, so these cells carry oxygen around the body.

A white blood cell that engulfs and digests bacteria and other foreign particles. It is part of the body's defence system and is attracted to sites of infection by chemicals released there.

One of millions of tiny air sacs in the lungs where gaseous exchange takes place. Its thin, moist wall and rich blood supply allow oxygen to diffuse into the blood and carbon dioxide to diffuse out.

The release of energy from glucose using oxygen, producing carbon dioxide and water. It happens in the mitochondria and supplies the energy needed for muscle contraction, growth and keeping warm.

The release of energy from glucose without oxygen. In human muscles it produces lactic acid, which builds up during hard exercise and causes tiredness and cramp until oxygen removes it.

The microscopic filtering unit of the kidney, of which each kidney contains about a million. It filters the blood, reabsorbs useful substances such as glucose and water, and collects urine for removal.

The control of the water and salt content of body fluids by the kidneys, guided by hormones. It keeps the concentration of the blood steady so that cells neither swell up nor shrink.

The widening of blood vessels near the skin surface, which increases blood flow and so increases heat loss. It happens when the body is too warm and helps bring the temperature back to normal.

The narrowing of blood vessels near the skin surface, which reduces blood flow and so reduces heat loss. It happens when the body is too cold and helps conserve heat.

A rapid, automatic response to a stimulus that does not involve conscious thought. A reflex arc passes from receptor through a sensory neurone, relay neurone and motor neurone to an effector such as a muscle.

The small gap between two neurones or between a neurone and a muscle. A chemical messenger diffuses across the gap to pass the impulse on, so signals travel in one direction only.

A chemical made by an endocrine gland and carried in the blood to a target organ, where it alters that organ's activity. Insulin, adrenaline, testosterone and oestrogen are examples.

A pair of muscles that work in opposition across a joint, such as the biceps and triceps at the elbow. When one contracts and shortens, the other relaxes and lengthens, producing movement.

A strong band of elastic tissue that joins one bone to another at a joint. It holds the bones in place while still allowing them to move against each other.

A tough, inelastic cord that attaches a muscle to a bone. It transmits the pull of the contracting muscle to the bone so that the joint moves.

A sex cell, either a sperm or an egg, containing half the normal number of chromosomes. Two gametes join at fertilisation to form a zygote with the full chromosome number.

The organ formed in the uterus during pregnancy, through which the fetus obtains oxygen and nutrients from the mother's blood and passes out carbon dioxide and urea.

A protein produced by white blood cells in response to a particular antigen. It binds to that antigen and helps destroy the pathogen, and it remains in the blood giving long-lasting immunity.

The introduction into the body of weakened or harmless forms of a pathogen, or their antigens. This stimulates white blood cells to make antibodies without causing the disease, so later infection is resisted.

One of the alternative forms of a gene that controls a characteristic, such as the alleles for brown or blue eye colour. An individual inherits two alleles, one from each parent.

An allele whose effect appears in the phenotype even when only one copy is present. It masks the effect of the recessive allele paired with it, so one copy is enough to show the characteristic.

The combination of alleles an organism carries for a particular characteristic, written as pairs of letters. It may be homozygous, with two identical alleles, or heterozygous, with two different ones.

A diagram showing the feeding relationship between organisms, with arrows pointing from each organism to the one that eats it. It begins with a producer and ends with a top carnivore.

An organism such as a bacterium or fungus that breaks down dead plants and animals. It releases minerals back into the soil so that producers can use them again.

The enrichment of water with nutrients such as nitrates from fertiliser, which causes rapid growth of algae. When these decay, oxygen is used up and fish and other animals die.