| Date | May 2013 | Marks available | 4 | Reference code | 13M.3.SL.TZ1.18 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 18 | Adapted from | N/A |
Question
Explain the consequences of releasing raw sewage and nitrate fertilizer into rivers.
Markscheme
a. raw sewage contains pathogens;
b. can contaminate drinking water / cause disease/death;
c. nitrate fertilizers cause algal blooms/(aquatic) plant development;
d. algae release toxins that can contaminate drinking water;
e. more organic matter results / eutrophication;
f. more oxygen required to decompose organic matter / increase in BOD;
g. (leading to) death of aquatic animals/organisms;
h. recovery follows since algae/plants release more oxygen;
Examiners report
Few candidates answered this option.
In (b) most candidates only scored one or two marks in this question as few could explain the consequences of releasing raw sewage and nitrate fertilizer into rivers.
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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