[BryanC]

What determines the metabolic pathways that a biological cell is able to carry?

For example:

• human cells, eukaryotes, utilize the Kreb's cycle to generate more ATP after glycolysis, but most bacteria cannot utilise the Kreb's cycle
• plant cells can carry out the Calvin's cycle for photosynthesis but human cells cannot.
• yeast can utilise the ethanol fermentation pathway but our human cells can only utilise the lactic acid fermentation pathway.

Why can't humans use the Calvin's cycle? Or why can't yeast use the lactic acid fermentation pathway instead? What determines the metabolic pathways that a biological cell is able to utilise?
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[Babcock_Hall]

Many bacteria (E. coli, for instance) do utilize the Krebs' cycle; therefore, your first bulleted point is debatable.  What have you come up with in terms of your own thoughts, so far?

[Arkcon]

Your question is so broad, as to be practically useless.  You ask "why" three times, with no work to show for it except ..."why?"

Consider:  Polar bears live much of their lives in the open Arctic.  I would die rapidly in that same situation.  We are both warm-blooded mammals.  We both lay down body fat as insulation, and we both grow hair.  Why don't I just grow more fat, fur and live in the open Arctic?

[Babcock_Hall]

@OP, What entities catalyze biochemical reactions?