| Date | November 2017 | Marks available | 6 | Reference code | 17N.3.HL.TZ0.18 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Discuss | Question number | 18 | Adapted from | N/A |
Question
Discuss the causes and consequences of eutrophication.
Markscheme
causes:
a. excess nutrients/nitrates/phosphates in an aquatic system
b. natural runoff from soil/erosion/weathering of rocks
c. runoff of fertilizers «from agricultural land/golf courses»
d. partially treated sewage/animal waste discharged into waterways
consequences: [4 max]
e. algal blooms
f. blocks light for photosynthetic organisms
g. dead organisms sink to bottom of water and decompose
h. decomposers/microorganisms increase BOD/use oxygen
i. oxygen/DO availability for other organisms decreases
j. decrease in biodiversity/disappearance of organisms
OWTTE
[Max 6 Marks]
Examiners report
[N/A]
Syllabus sections
Option C: Ecology and conservation » Option C: Ecology and conservation (Additional higher level topics) » C.6 Nitrogen and phosphorus cycles
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