Biology Pollution

Pollution

Grade 8

You learned about pollution. Pollution means adding things to the environment that harm living organisms.

Let's look at one example of pollution, and think about how it affects food webs, decomposers and the population of living organisms.

Effects of fertilisers pollution in water

Step 1 fertiliser added to a lake

A farmer sprays fertiliser into a field to help his crops to grow better. By mistake, some of the fertiliser get onto a lake.

Step 2 Increased growth of water plants and algae

The fertiliser makes the algae and plants in the lake grow faster. (Algae are very simple plant-like organisms.) Their population increase. This is known as an algal bloom.

Step 3 Plant die

The big populations of plants and algae cover the water. They stop light getting to the plants underneath them. Many plants die.

Step 4 Increase in decomposers

All the dead plants provide extra food for decomposers. The numbers of decomposers increase. Populations of bacteria get very large. The bacteria all respire, using up most of the dissolved oxygen in the water.

Step 5 Death of fish

Now there is so little oxygen in the water that most animals cannot live there. Fish die. Only animals that are adapted to live in low oxygen concentrations can survive.

Open Ended

What do fertilisers contain, that make plant and algae grow faster?

Ans: Mineral salts, for example nitrate, potassium and phosphate.

Open Ended

Explain why the plants die when they do not get enough light.

Ans: Plants need light for photosynthesis. If they cannot photosynthesise, they cannot make any food, so they die.

Open Ended

Explain why the population of bacteria in the water increases after the plants die.

Ans: The bacteria are decomposers. They get their energy by feeding on dead plants. If there are more dead plants, the bacteria can reproduce more quickly

Open Ended

Explain why fish die when they do not get enough oxygen.

Ans: Fish need oxygen for respiration. If they cannot respire, they have no energy and will die.

Open Ended

Suggest what happens to the populations of birds that feed on fish.

Ans: The population of birds that feed on fish will decrease.

Open Ended

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.

Ans:  The algal bloom occurs where there are high concentrations of mineral ions in the sea. Fertilisers have run into the sea from the land.

Summary

• Pollution is the addition of harmful substances to the enviroment.

• 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.

Watch this video

https://www.youtube.com/watch?v=706kZXlHZRw