Human Biology - EDEXCEL IGCSE - Environment

Environment:

Humans inhabit many of the Earth’s ecosystems. An ecosystem is a distinct, self-supporting system interaction with each other and with their physical environment.

Ecosystems have:

• Producers - green plants that photosynthesise.
• Consumers - animals that eat plants or other animals.
• Decomposers - Microorganisms that break down dead material and help in recycling nutrients.
• Physical environment - the non-biological components such as water, soil and air.

Plants are the source of all the food that animals, including humans, eat. They also create oxygen which aerobic organisms need for respiration. Plants can create from glucose, starch, sugars such as fructose or sucrose, cellulose and lipids.

Photosynthesis:

Carbon Dioxide + Water —> Glucose + Oxygen

Food chains are made up of trophic levels:

Producer —> consumer—> decomposers

Energy and substances are transferred along a food chain. Every time energy is transferred, a large amount of it is lost through the lack of digestion and therefore passes out as faeces. Some form excretory products such as urea and some is respired to release energy. Not only this, but a large amount of energy is also lost through respiration. Because of this, only around 10% of energy is used to create new cells and therefore can be passed on to the next trophic level.

Transfer of energy:

1. Photosynthesis creates glucose.
2. Respiration releases energy from compounds such as glucose.
3. Almost all biology processes use the energy released in respiration.
4. If the energy is used to create new cells then it can be passed on to the next trophic level.
5. If not then once used it will eventually escape as heat.

Food preparation, storage and preservation:

Preparation: cooking food properly to kill any microorganisms present.

Storage:

• Packaging of food to prevent transmission of microorganisms.
• Display before and best before dates to tell you when the food is unsafe to eat.
• Placing cooked and raw food separately.
• Not refreezing after cooking as bacteria will multiply very quickly.
• Food should not be left open to the air on a work surface.

Preservation:

• Salting - bacteria lose water by osmosis and are killed. (e.g.fish, some meats)
• Pickling - food butler in vinegar (ethanoic acid). The low pH inactivates most microorganisms.
• Pasteurisation - 63-65°C for 30 minutes or 71.5°C for 15 seconds (milk)
• Canning - packed in cans, heated, sealed, then finally heats to 105-160°C. (e.g. soup, beans).
• Drying - blowing hot air to remove water (e.g.cereal, grains)
• Freezing - frozen to -10°C rapidly (e.g. meats, prepared meals)
• Irradiation - high energy gamma rays are passed through food (e.g.potatoes, onions)

Water purification:

1. Water is taken from a source.
2. It is then passed through a screen to filter large solid objects such as weeds and other debris.
3. It is pumped to a settling tank for particles to settle. The sludge is removed at intervals and used as fertiliser or in landfill.
4. Pumped to a filter bed where it is sprayed onto it from a revolving arm. It slowly trickles down from sand at the top to stones and gravel at the bottom. Bacteria and fungi among the particles break down any organic matter and protozoa feed on the bacteria, including pathogens.
5. Chlorine is added to kill any remaining pathogens.
6. It is then stored in covered reservoirs which prevent the growth of algae and contaminants from entering.
7. Water is finally pumped to homes.

Air pollution:

Carbon Monoxide:

This is a colourless, odourless and tasteless gas which can cause death by asphyxiation. Haemoglobin bind with this rather than oxygen and so a person may become unconscious if it’s breathed in for a certain time as a result of a lack of oxygen.

Sulfur Dioxide:

This is a major constituent of acid rain which kills plants and also ruins the landscape.

Green House Gases:

These include water vapour, carbon dioxide, nitrous oxide, methane and CFCs (chlorofluorocarbons).

The level of greenhouse gases has risen rapidly in the past 100 years. The increasing burning of fossil fuels such as coal, oil and natural gases as well as petrol and diesel in vehicle engines has led to this. The increasing deforestation also means that the greenhouse gas carbon dioxide is used less in photosynthesis.

The increasing levels of greenhouse gases have resulted in the enhanced greenhouse effect. The normal greenhouse effect is where gases absorb some long wavelength infra-red radiation from the sun and re-emit some as longer wavelength IR. This heats up the surface of the Earth. However, with too much greenhouse gases, global warming has occurred where the earth heats up quicker than it should. This has caused the melting of the ice caps and, therefore, sea level rises, changing ocean currents meaning warm water is redirected to cooler areas, more rainfall in some areas (climate changes), species to become extinct as they cannot adapt fast enough and changes to agricultural practices as some pests become more abundant.

Deforestation:

Each year tens of thousands of hectares of rainforests are cut down. This causes several problems:

• Soil erosion occurs as it is exposed due to lack of a canopy meaning the soil is down or washed away.
• Leeching occurs where minerals are washed out by rain. This occurs as there are no tree roots to hold the soil together.
• Destruction of habitats and reduced biodiversity occurs. Around 50-70% of all species live in rainforests.
• The water cycle is disturbed as trees are an important part of returning water vapour from the soil.
• The balance in atmosphere oxygen and carbon dioxide changes as photosynthesis decreases. This will cause global warming.