| Date | May 2015 | Marks available | 4 | Reference code | 15M.3.SL.TZ2.18 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | Explain | Question number | 18 | Adapted from | N/A |
Question
State the role of Rhizobium, Nitrobacter and Azotobacter in the nitrogen cycle.
Rhizobium: .....................................................................
Nitrobacter: .....................................................................
Azotobacter: .....................................................................
Explain the production of methane from biomass.
Markscheme
a. Rhizobium: nitrogen fixation;
b. Nitrobacter: oxidizes/changes nitrites to nitrates;
c. Azotobacter: nitrification / bind atmospheric nitrogen / nitrogen fixation;
a. anaerobic digestion of biodegradable material;
b. fermentation (of carbohydrates) by bacteria;
c. methanogens produce methane;
d. methane/biogas used as energy;
e. waste products used as fertilizer;
f. CO2 produced (as a by-product);
Examiners report
N/A
Some students gave comprehensive explanations of the production of methane from biomass. Most students scored at least one point.
