Question

multiple choice question
where do methanogens get the hydrogens involved in reducing co₂ to ch₄ in anaerobic respiration?
from organic molecules that they produce
from fermentation
from organic molecules produced by other organisms
from photosynthesis that they conduct

Explanation:

Methanogens obtain hydrogen for reducing CO₂ to CH₄ from fermentation processes. Fermentation can produce hydrogen - rich compounds that serve as hydrogen donors in this anaerobic respiration process. Methanogens are not photosynthetic, and they don't produce the necessary organic molecules on their own for this hydrogen - donation purpose in the context of this reaction. Also, they don't rely on organic molecules produced by other organisms for the hydrogen in this specific reduction reaction.

Answer:

From fermentation