| Date | November 2012 | Marks available | 2 | Reference code | 12N.3.SL.TZ0.18 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Outline | Question number | 18 | Adapted from | N/A |
Question
Outline the role of saprotrophic bacteria in the treatment of sewage.
Markscheme
saprotrophs/decomposers feed on/break down organic material;
requires high oxygen/aerobic environment;
nitrifying bacteria convert ammonia to nitrates;
trickle filter bed/reed bed systems optimize environment for saprotrophs;
Examiners report
In (b) (i), there were many poor responses on sewage and the role of saprotrophs.
Syllabus sections
Option B: Biotechnology and bioinformatics » Option B: Biotechnology and bioinformatics (Core topics) » B.3 Environmental protection
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