DP Biology (last assessment 2024)

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Question 23M.3.HL.TZ1.14

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Date May 2023 Marks available [Maximum mark: 6] Reference code 23M.3.HL.TZ1.14
Level HL Paper 3 Time zone TZ1
Command term Explain Question number 14 Adapted from N/A
14.
[Maximum mark: 6]
23M.3.HL.TZ1.14

Explain how bacteria of the genus Pseudomonas can be used in bioremediation of aquatic environments.

[6]

Markscheme
  1. bioremediation involves using microorganisms to return a polluted environment to its natural state;
  2. Pseudomonas can be used in the treatment of oil spills (in marine environments);
  3. the bacteria are sprayed directly onto the oil;
  4. the bacteria use the hydrocarbons in crude oil as carbon/energy source/for respiration;
  5. breaking them down into carbon dioxide and water;
  6. process can be accelerated by providing the bacteria with essential nutrients/nitrates;
  7. mercury released into aquatic ecosystems by industrial processes/coal-fired power plants/ in garbage dumps in paints/light bulbs;
  8. can be converted into methyl mercury;
  9. methyl mercury runs off into / bioaccumulates in aquatic systems;
  10. Pseudomonas can break down methyl mercury to elemental mercury and methane gas;

a. OWTTE

Examiners report

Many candidates were able to earn one or two marks for showing some idea of how Pseudomonas could be used in remediating oil spills. However, details were not known. Almost none of the responses mentioned the role of Pseudomonas in the breakdown of methyl mercury which enters aquatic systems from industrial processes.