Recycling of solid wastes — A/L Biology

How do I practise Recycling of solid wastes?

1 question with a worked solution

1. During the anaerobic biomethanation of organic municipal solid waste in a commercial biodigester, which microbial group performs the terminal biochemical step converting acetate, hydrogen, and carbon dioxide into methane gas?
   1. A) Acetogenic sulfate-reducing bacteria
   2. B) Acidogenic fermentative bacteria
   3. C) Methanogenic archaea (Methanogens)
   4. D) Hydrolytic cellulolytic fungi
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   Correct answer: C) Methanogenic archaea (Methanogens)

   Anaerobic digestion proceeds through four stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. In the final stage, obligate anaerobic Methanogenic archaea (e.g., Methanobacterium, Methanosarcina) reduce acetate (acetoclastic methanogenesis) or CO₂ + H₂ (hydrogenotrophic methanogenesis) to produce combustible CH₄ and CO₂ (biogas).

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   Step 1: Trace stages of anaerobic digestion: 1. Hydrolysis (polymers -> monomers by hydrolytic bacteria) 2. Acidogenesis (monomers -> volatile fatty acids) 3. Acetogenesis (fatty acids -> acetic acid, CO₂, H₂) 4. Methanogenesis (acetate/CO₂/H₂ -> CH₄ + CO₂ by Methanogens) Answer: Methanogenic archaea (Methanogens).
   Modelled on: the A/L Biology examination pattern

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Where does Recycling of solid wastes fit in the syllabus?

Year 2 · Term 3