Page 37 - Science Coursebook

2.7 Pollution

The algae that cause algal blooms This photo was taken by a NASA satellite. It
often produce toxic chemicals. Animals shows the Black Sea. The green colour around

that drink the water may be poisoned. the edges is caused by an algal bloom.
Questions
1 What do fertilisers contain, that make plants and algae grow faster?
2 Explain why the plants die when they do not get enough light.
3 Explain why the population of bacteria in the water increases after the
plants die.

A+I 4 Explain why fish die when they do not get enough oxygen.

A+I 5 Suggest what happens to the populations of birds that feed on fish.
6 Look at the satellite photograph of the Black Sea. Suggest why the algal
bloom is around the edges of the sea, rather than spread all over it.

Activity 2.7
Pollution poster

Most farmers try not to pollute lakes and rivers with fertilisers. Fertilisers are
expensive, so they do not want to waste them. But it is easy to make a mistake.
Make a poster to go on the wall of a store where farmers come to buy fertilisers.
Your poster should:
• catch the eyes of the farmers
• explain clearly why they should not let fertilisers get into lakes or rivers
• tell them what clues to look out for that would show that pollution may have
happened.

Summary
• Pollution is the addition of harmful substances to the environment.
• Adding fertilisers to water can cause algal blooms.
• When the algae die, bacteria feed on them, using up the oxygen that
was dissolved in the water.
• Aquatic animals may die, or move away, because they cannot get
enough oxygen.

2 Living things in their environment 35