(a) Based on the Diagram , explain what ia meant by`eutrophication'.[10 m)
(b) Explain how each of the following can reduce water pollution:
(i) Treating sewage
(ii) Using organic fertilizers rather than inorganic ones. [6 marks]
(c) Explain why rainforest ecosystem has to be maintained. [4m]
Suggested Answer:
Able to explain eutrophication.
Sample answer
(a) P1 : Farmers use fertilizers that usually contains nitrates/phosphate
P2: Fertilizer/animal waste/silage which contain nitrate/phosphate may washed out in water when it rains/leaching/run into the lake.
P3: Algae/green plant in the lake grow faster (when they are supplied with extra nitrate/(phosphate)
P4: (they may grow so much) that they completely cover the water.
P5: block out the light for plants growing beneath them.
P6.Photosynthesis rate reduced
P7:Dissolve oxygen also reduced
P8: Plant on the top of water and beneath water eventually die.
P9: Their remains are good source of food bacteria //bacteria decomposed the dead plant rapidly//bacteria breed rapidly
P10:The large population of bacteria respires, using up oxygen ,so there is very little oxygen left for other living organism
P11: BOD increased
P12: Those fish which need oxygen have to move other areas or die
[ Any 10 ]
(b) (i) Treating sewage
P1: The sewage contains harmful bacteria /substance which provide
Nitrate/nutrient for microbe.
P2: Remove harmful bacteria/most of the nutrient which could course eutrophication before it is released into the rivers.
P3: When sewage has been treated, the water in it can be used again//sewage treatment enables water to be recycled.
P4: Microorganisms used in sewage treatment. Any 3
ii) Using organic fertilizers rather than inorganic
Sample answer
1. Example of organic fertilizers : Manure
2. Example of inorganic fertilizer : Ammonium nitrate
3. Organic fertilizers do not contain many nitrates(which can easily be leached out of the soil.
4. They release their nutrients gradually (over a long period of time) giving crops time to absorb them efficiently. [ Any 3]
Able to explain the relation between deforestation and flash flood
Sample answer
F ; deforestation can cause soil erosion
P1 : The leafy canopy trees protect the soil from the impact of falling rain.
P2: The roots of the trees hold soil and water
P3: (With the trees removed) the soil is exposed directly to the rain//water runoff becomes intense.
P4:Topsoil/fertile layer,get washed away during heavy rain.
P5: (heavy rainwater flows down hillside to river with) eroded soil deposited blocking the flow of water.
P6: The water levels in rivers rise rapidly causing flood to occur. [ Any 4]
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