Biology - Humans and the Enviornment

Pollution defintion

The addition of substances to the environment which harms life

Air pollution examples

Sulphur dioxide and Carbon monoxide

Sulphur Dioxide SO₂ problem

It reacts with water in the clouds to form sulfuric acid which can fall as acid rain. Wind can carry rain clouds many miles and the acid rain falls on the countryside, making ponds, rivers and lakes more acidic. Acid rain damages the leaves of plants and kills fish

Carbon Monoxide CO problem

It’s released from car exhausts due to incomplete combustion. It’s dangerous due to it being a colourless, odourless and poisonous gas. When it’s breathed in, it enters the blood and binds irreversibly with haemoglobin. This means less oxygen is carried by red blood cells so tissues and organs receive less oxygen for respiration so if a lot of CO is inhaled, the person can die from a lack of oxygen

Water pollution examples

Sewage, fertilisers

Sewage problem

More sewage = more microorganisms such as bacteria and fungi which breaks down the sewage. This microorganisms reproduce and respire, using up all the oxygen in the water. This kills the fish so the number of fish in the river decreases

Fertilisers problems

Leaching, eutrophication

Leaching problem

When the nitrates (which are very soluble in water) are washed out of the soil when it trains into the river

Eutrophication problem

When the nitrates are absorbed by the green algae in the water which multiply rapidly and may completely cover the water, which is called algae bloom. It then blocks out sunlight for other plants which are unable to photosynthesise and die. The algae then dies too. The dead remains provide a good source of food for bacteria which multiply rapidly, using up all the oxygen in the water, killing other organisms in the water e.g. fish

Deforestation definition

When people cut down forests to grow food to earn a loving or sell the timber to generate income

Effects of deforistation

Soil erosion, patterns of rainfall, balance of CO₂ and O₂ in the air, destruction of habitats

Soil erosion problem

Without trees there are no leaves to shield the soil directly from the rain and no roots to bind the soil together. When raindrops hit the soil, they wash it away and this erosion might cause the silting of rivers and leads to flooding

Patterns of rainfall problem

Water evaporates from leaves in a process called transpiration therefore fewer trees = less transpiration therefore less rainfall and even drought

Balance of CO₂ and O₂ problem

Fewer trees = less photosynthesis therefore less CO₂ is removed from the air therefore less O₂ released into the air therefore the balance changes

Destruction of habitats problem

Fewer trees = loss of habitats and loss of food for animals which may lead to extinction

Examples of greenhouse gases

Carbon dioxide, water vapour, nitrous oxide, methane, CFCs

How are humans increasing amount of greenhouse gases?

Combustion of fossil fuels (cars) releases carbon dioxide and nitrous oxide; aerosols releases CFCs; deforestations = more carbon dioxide in the air

How do greenhouse gases cause global warming?

Infra-red is reflected by the gases in the atmosphere back to earth. The temperature of the earth rises. This is called enhanced greenhouse effect and leads to global warming.

Consequences of global warming

• Ice caps melt

• Sea levels rise

• Flooding

• Habitats and food for animals are lost

• This may lead to a change in the distribution of animals as they move away to find new habitats

• It may even cause extinction