Biology revision bites

Water is lost when we exhale, it leaves the skin when we sweat, and is also lost in urine from the kidneys.

FSH stands for follicle stimulating hormone and is first in the menstrual cycle. It is secreted by the pituitary gland and causes the ovaries to mature the eggs. It also starts the production of oestrogen.

The eyes detect colour, shape, light and motion. Ears detect pitch, vibration, sound, amplitude and pressure (balance). The nose detects smell and the tongue detects taste. Skin detects pain, pressure, temperature and texture.

Trees take in carbon dioxide and give out oxygen, which keeps the right level in the atmosphere. Forests also store water, because leaves slow the evaporation process. Deforestation changes these mechanisms.

Fertiliser is used to grow crops. When it rains, it is leached from the soil into rivers. Algae then dies and rots, and decomposers thrive in the river bed, consequently using up the oxygen. Fish and invertebrates therefore die of oxygen starvation.

Pesticides like DTT are used to kill insects. These are dangerous as they don't break down in the food chain, so they remain in the atmosphere.

Habitats are destroyed for housing space, land is quarried to extract rocks, and land is used for energy by building dams and flooding land for hydroelectricity.

Genetic modification is costly for companies and customers, insects may develop pesticide resistance, herbicide resistance may pass to weeds, there are allergy risks and unknown effects on health, and it may harm other organisms.

Plants may be resistant to pests and herbicides, crops may contain additional nutrients, plants may withstand extreme conditions, and may be resistant to disease.

Genes carry information from parents and are passed on by gametes. They are carried on chromosomes and control characteristics.

Once taken, they should be taken for life. They reduce the amount of cholesterol you produce, so cells take it from the blood. They reduce risk of heart disease and stroke by a third.

Alcohol is a depressant, which can cause brain damage, cancer and antisocial behavior. It affects the heart and circulation, mental health, lungs, liver, fertility, stomach, bones, intestines, pancreas and kidneys.

Cigarettes contain nicotine, tar and other chemicals. It affects circulation, skin, fingers and teeth, the brain, fertility, and the immune system. It causes emphysema, heart disease and cancer, and can damage unborn babies.

Cannabis affects the brain and has the same effects as nicotine, including a big impact on mental health.

Steroids enhance performance, but they can cause aggression, acne, liver disorders, hair loss, hypertension (high blood pressure), raised cholesterol and tumours.

Word equation: glucose + oxygen → carbon dioxide + water (+ energy)

Symbol equation: C6H12O6 + O2 → CO2 + H2O (+ energy)

Decomposers are organisms which feed on waste and dead animals. Examples are bacteria and fungi. They release CO2, water and minerals as waste, which plants use to grow and develop.

Decay is vital for recycling natural resources, and it helps us recycle waste. It breaks down waste in sewers and rots material in compost heaps; compost is used as plant fertiliser.

Carbon dioxide is removed by plants to make up nutrients, and released in plant respiration. Carbon from animals is released in animal respiration, and dead organisms feed the animals, who consume the carbon in the dead organisms. By the end of the whole decay process, all original energy from the plants has been transferred. Carbon dioxide is also released when fossil fuels are burned.