| Date | November 2017 | Marks available | 6 | Reference code | 17N.3.HL.TZ0.18 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 / no time zone |
| 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
Syllabus sections
-
19N.3.HL.TZ0.17a:
The figure below shows the effects of soil pH on nutrient availability. Thicker bars indicate higher nutrient availability.
[Source: diagram drawn from Emil Truog, 1947, The Liming of Soils, USDA Yearbook of Agriculture 1943–1947,
and N.A. Pettinger, 1935, A Useful Chart for Teaching the Relation of Soil Reaction to the Availability of Plant
Nutrients to Crops, Virginia Cooperative Extension, Virginia Tech, and Virginia State University]Identify which element is more available in strongly acid conditions.
- 16N.3.SL.TZ0.14a: Outline the trend in the number of people with malaria during the period when the use of...
- 20N.3.HL.TZ0.19: Suggest how nitrogen and phosphate cycles can be disrupted by humans or extreme weather events.
- 17M.3.HL.TZ1.16a: Some scientists estimate that available phosphorus reserves in the Earth will be completely...
- 19N.3.HL.TZ0.17b: Outline the roles of Rhizobium bacteria in the nitrogen cycle.
- 17M.3.HL.TZ1.16b: The percentage of phosphorus in an ecosystem that is recycled per year is in most cases very...
- 18N.3.HL.TZ0.16b: Explain how eutrophication can occur from the excessive use of phosphates.
-
18M.3.HL.TZ1.18:
Explain how human activities could affect the phosphorus cycle.
- 18N.3.HL.TZ0.17: Explain how an ecological community structure could be affected by the removal of a keystone...
- 18N.3.HL.TZ0.16a: Describe reasons that the availability of phosphates may become limiting to agriculture in...
- 17M.3.HL.TZ2.15d: A coat of algae builds up on coral reefs as a consequence of eutrophication. Explain the...
- 16N.3.HL.TZ0.18: Discuss how crop plants obtain the phosphorus that they need to grow and whether the supply...
-
19M.3.HL.TZ2.18:
Commercial fertilizers are often applied to agricultural land. Discuss the use of fertilizers on crops and their effect on other ecosystems.
- 19N.3.HL.TZ0.17c: Describe the major characteristics of a eutrophic lake.
