Question 19M.3.HL.TZ1.11
| Date | May 2019 | Marks available | [Maximum mark: 4] | Reference code | 19M.3.HL.TZ1.11 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Identify, Outline, State, Suggest | Question number | 11 | Adapted from | N/A |
Some halophilic bacteria biodegrade benzene, which makes them useful in treating oil spills as benzene is contained in crude oil. Investigators added cultures of the bacteria to benzene solutions at different salinities in containers. The amount of benzene remaining in the container was recorded once a week for two weeks.
[Source: adapted from C A Nicholson and B Z Fathepure, (2004),
Applied and Environmental Microbiology, 70 (2), pages 1222–1225]
Outline what is meant by halophilic when describing the bacteria.
[1]
thrive/live in a salt rich environment ✔
(a) to (c) These three questions were often answered well.
Identify the salt concentration with the greatest rate of benzene biodegradation.
………………......… mol m–3
[1]
1 mol m–3 ✔
(a) to (c) These three questions were often answered well.
State one genus of halophilic bacteria known to biodegrade benzene.
[1]
Marinobacter ✔
Allow other correct responses eg: Dechloromonas, Haloferax, Pseudomonas, Fusarium, Halomonas, Halococcus,
Halobacterium, Haloarcula, Haloarchaea, Fundibacter, Fusarium, Alcanivorax, Dietzia
(a) to (c) These three questions were often answered well.
Suggest one advantage to the bacteria of breaking down benzene.
[1]
a. energy gained from the benzene ✔
b. benzene acts as a source of carbon ✔
Very few students could state that the breakdown of benzene could be used as a source of carbon or energy.