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Question 18N.3.HL.TZ0.16b

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Date November 2018 Marks available [Maximum mark: 3] Reference code 18N.3.HL.TZ0.16b
Level HL Paper 3 Time zone TZ0
Command term Explain Question number b Adapted from N/A
b.
[Maximum mark: 3]
18N.3.HL.TZ0.16b

The pie chart shows the world demand for phosphorus in 2010. The fraction used as detergents and in industries has decreased in recent years in response to evidence that phosphate pollution of surface waters causes eutrophication.

(b)

Explain how eutrophication can occur from the excessive use of phosphates.

[3]

Markscheme

a. phosphates are leached to lakes/rivers ✔

b. induces incremental growth of plants/bloom/algae ✔

c. algae do not let light go through water so less photosynthesis ✔

d. plants/algae die/decay ✔

e. bacterial decomposition consumes the oxygen ✔

f. creating state of hypoxia
OR
greater biochemical oxygen demand ✔

g. causing death of «aerobic» organisms ✔
eg: fish

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