| Date | May 2012 | Marks available | 2 | Reference code | 12M.3.HL.TZ1.8 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | List | Question number | 8 | Adapted from | N/A |
Question
The diagram below represents the cell walls of two different bacteria. State, with a reason, which cell wall (I or II) is Gram-positive.
Microorganisms play many roles in ecosystems. List two of these roles.
1. ..................................................................
2. ..................................................................
Markscheme
I (is Gram-positive) because it has thick/outer layer of peptidoglycan/does not have outer layer (of lipids) external to peptidoglycan layer
producers / food source in aquatic environments;
nitrogen fixers / denitrifiers;
decomposers;
methane producers;
Examiners report
Many candidates were able to correctly indicate that the diagram was of a Gram-positive bacterium and why.
It was surprising that many candidates did not get the two marks for listing two roles of microorganisms in the environment as this was very basic.
