Secondary 6 Biology

The physical breakdown of food by chewing and peristalsis, which grinds and mixes it without changing its chemical nature.

The process by which digestive enzymes break carbohydrates, proteins and lipids into small, absorbable molecules.

The enzyme in saliva that breaks starch down into maltose in the mouth.

The breaking of large fat masses into tiny droplets by bile, enlarging the surface for lipase; bile itself contains no enzyme.

A finger-like projection of the small intestine wall containing capillaries and a lacteal, greatly enlarging the absorbing surface.

Tiny projections on the epithelial cells of villi that enlarge the absorbing surface even further.

A tiny pouch at the end of the airways where gas exchange takes place; thin-walled, moist and wrapped in capillaries.

The muscular sheet dividing chest from abdomen; when it contracts and flattens it drives inhalation.

The movement of air into and out of the lungs, driven by pressure differences created as the chest volume changes.

The removal of undigested, unabsorbed food remains (faeces) from the body through the anus.

The circulation in which blood passes through the heart twice per full tour, comprising the systemic and pulmonary circulations.

An upper chamber of the heart that receives returning blood and passes it into the ventricle.

A lower chamber of the heart that pumps blood out; the left ventricle has the thickest wall.

Structures ensuring one-way blood flow — the atrioventricular valves (tricuspid and bicuspid) and semilunar valves — preventing backflow.

The artery supplying the heart muscle with oxygen and nutrients; its blockage starves the muscle and causes a heart attack.

A vessel carrying blood away from the heart; thick-walled with much muscle and elastic fibre to withstand high pressure.

A vessel returning blood to the heart at low pressure, with thinner walls and valves that prevent backflow.

A tiny vessel whose wall is a single flattened cell; with the slowest flow, it is where blood and cells exchange materials.

The iron-containing pigment inside red blood cells; it binds oxygen in the lungs and releases it in tissues where oxygen is scarce.

Fluid formed as plasma water and solutes leak through the capillary wall, bathing the cells and mediating exchange.

A structure that detects a stimulus and converts it into nerve signals, such as the light-sensitive cells of the retina.

The basic unit of the nervous system — sensory, intermediate or motor — transmitting information as electrical impulses.

The signal route of a reflex: receptor → sensory neurone → centre → motor neurone → effector, five stations in all.

The junction between two neurones, where chemicals pass the signal one way to the next neurone.

A chemical messenger secreted by an endocrine gland directly into the blood, acting at its target organ.

A ductless gland that secretes hormones straight into the blood, such as the islets of the pancreas and the thyroid.

The maintenance of a relatively stable internal environment (blood glucose, body temperature, water and so on).

A mechanism that detects a deviation from the normal level and corrects it in the opposite direction.

A pancreatic hormone that promotes glucose uptake by cells and its conversion to glycogen in the liver, lowering blood glucose.

A pancreatic hormone that makes the liver break glycogen into glucose for release into the blood, raising blood glucose — the opposite of insulin.

A reproductive cell for sexual reproduction — sperm in the male, egg in the female — each carrying half the chromosomes.

The union of a sperm and an egg in the oviduct, their nuclei fusing to form a fertilised egg.

The release of a mature egg from the ovary, triggered by the peak of luteinizing hormone around day fourteen of the cycle.

The roughly twenty-eight-day cycle of changes during a woman's fertile years — thickening of the uterine lining, ovulation and shedding.

A hormone secreted by follicles that builds and repairs the uterine lining, preparing it for implantation.

A hormone from the corpus luteum that maintains the uterine lining; if implantation occurs its level stays high and menstruation does not come.

The embedding of the dividing fertilised egg into the thickened uterine lining after several days.

The organ of exchange between mother and foetus: their bloods never mix, and oxygen, nutrients and wastes move across by diffusion.

The fluid surrounding the foetus, cushioning shocks, protecting it and keeping a stable temperature.

A curve of a growth parameter such as mass or height against time, used to identify the stages of growth.

All the individuals of one species within a given area and time.

All the populations sharing an environment, interacting through various relationships.

The system formed by a community interacting with its abiotic environment — the basic unit of ecological study.

The natural environment in which an organism or population lives, with its own abiotic conditions.

An autotroph such as a green plant or alga that converts light energy into chemical energy by photosynthesis — the start of every food chain.

A heterotroph that feeds on other organisms, covering herbivores and carnivores.

An organism — chiefly bacteria and fungi — that breaks dead bodies and wastes into inorganic matter, returning materials to the cycle.

The feeding position a link occupies in a food chain: producers first, herbivores second, then successive carnivore levels.

The network formed by interlinked food chains, showing how species depend on one another.

The directional change of a community over time, from pioneer species to a stable climax community.

An organism that causes infectious disease — viruses, bacteria, fungi and protists.

A disease caused by pathogens and transmissible between people through water, air, droplets, food, body fluids or vectors.

A substance on a pathogen that the immune system recognises, triggering an immune response.

A protein made by B cells against a specific antigen, binding it and disabling the pathogen.

The white blood cells of specific immunity — B cells that make antibodies and T cells that attack infected cells.

Immunity in which the body makes its own antibodies and memory cells after meeting the antigen, as after vaccination — lasting but slower to arise.

Immunity gained by injecting ready-made antibodies, as with tetanus antitoxin or antibodies in breast milk — immediate but short-lived.

Injecting weakened or killed pathogens, or their antigens, to induce active immunity and prevent infectious disease.

The survival and spread of bacteria selected by antibiotic overuse, making the drugs ineffective.

A disease that never passes between people — cancer, coronary heart disease and diabetes — linked to genes and lifestyle.