B13 - Human influences on ecosystems

Question 1

What is eutrophication?

Answer 1

The sudden increase in the nutrient content of a lake or river.

Question 2

What are the 10 steps of eutrophication?

Answer 2

1) Farmer adds nitrate fertiliser to farmland. Nitrates increase plant growth and profit.
2) Rain pours on the soil and soluble nitrates are washed into a lake/river.
3) Nitrates in the lake cause the rapid growth of algae on the lake’s surface.
4) A thick ‘blanket’ of algae covers the lake’s surface and blocks light to the plants below. This is an algal bloom.
5) The blanket of algae die due to their short life cycle.
6) There is an increase in the dead material in the lake due to the dead surface algae and the plants below.
7) The decomposers, bacteria and fungi, feed on the dead material, increasing their number.
8) Decomposers are aerobic, using up oxygen in respiration. Large numbers of decomposers are respiring, reducing the lake’s oxygen level.
9) Oxygen level in the lake falls.
10) Aerobic organisms die.

Question 3

What is bioaccumulation?

Answer 3

When chemicals don’t break down in living organisms, so they build up in food chains.

Question 4

What is biomagnification?

Answer 4

The increase in concentration up the food chain.

Question 5

What is the carbon cycle?

Answer 5

How carbon is taken in by plants through photosynthesis and then passed along the food chain while partially being released back into the atmosphere at the same time. Eventually, it all gets back into the air and starts the cycle again.

Question 6

What five problems does deforestation cause?

Answer 6

1) Reduction in soil fertility.
2) Flooding and landslides.
3) Changes in the recycling of materials.
4) Climatic changes.
5) Species extinction.