The Most Ancient CO₂ Fixation Pathway in Methanogens is The

Question

The most ancient CO₂ fixation pathway in methanogens is the
A) reverse TCA cycle.
B) 3-hydroxypropionate cycle.
C) Calvin cycle.
D) reductive acetyl-CoA pathway.
E) Krebs cycle.

Accepted Answer

The most ancient CO₂ fixation pathway in methanogens is the reductive acetyl-CoA pathway, which is also known as the Wood-Ljungdahl pathway. This pathway is used by methanogenic archaea to convert CO₂ into methane. The reverse TCA cycle, the 3-hydroxypropionate cycle, and the Calvin cycle are carbon fixation pathways used by other organisms, not methanogens. The Krebs cycle is not involved in CO₂ fixation.