10. In prokaryotes, the terminal electron acceptor in anaerobic conditions are generally
(1) Glucose, fructose,  maltose
(2) Fatty acids
(3) SO₄^2-,  NO₃^2- , S
(4) Antioxidants such as Vitamin K

In prokaryotes, respiration is a vital process for energy production. While aerobic respiration uses oxygen as the terminal electron acceptor, many prokaryotes live in environments devoid of oxygen and rely on anaerobic respiration. Under these conditions, they use alternative terminal electron acceptors to sustain their metabolism and generate ATP.

What Are Terminal Electron Acceptors?

Terminal electron acceptors are molecules that receive electrons at the end of the electron transport chain during respiration. In aerobic respiration, oxygen serves this role due to its high reduction potential and availability. However, in anaerobic environments, oxygen is absent or limited, and prokaryotes use other compounds with lower reduction potentials.

Common Terminal Electron Acceptors in Anaerobic Prokaryotes

Prokaryotes utilize a variety of inorganic molecules as terminal electron acceptors in anaerobic respiration, including:

• Sulfate (SO4^2−): Reduced to hydrogen sulfide (H2S) by sulfate-reducing bacteria.

• Nitrate (NO3−): Reduced to nitrogen gas (N2) or nitrous oxide (N2O) through denitrification processes.

• Elemental sulfur (S): Reduced to hydrogen sulfide (H2S) by certain bacteria and archaea.

These acceptors enable the electron transport chain to function without oxygen, though the energy yield is generally lower than aerobic respiration.

Why Not Organic Molecules or Antioxidants?

• Glucose, fructose, maltose: These are electron donors (fuel molecules), not electron acceptors.

• Fatty acids: Primarily serve as energy sources, not terminal electron acceptors.

• Antioxidants like Vitamin K: Function in protecting cells from oxidative damage, not as terminal electron acceptors in respiration.

Supporting Evidence from Microbial Metabolism

• Anaerobic respiration involves electron transport chains similar to aerobic respiration but uses alternative acceptors such as nitrate, sulfate, and sulfur.

• These molecules have lower redox potentials compared to oxygen, resulting in less ATP per glucose molecule.

• This process is ecologically significant in nitrogen, sulfur, and carbon cycling in various environments like sediments, soils, and aquatic systems.

Summary Table

Conclusion

Under anaerobic conditions, prokaryotes typically use inorganic molecules such as sulfate (SO4^2−), nitrate (NO3−), and elemental sulfur (S) as terminal electron acceptors. These molecules enable the continuation of electron transport and ATP synthesis in the absence of oxygen.

Final Answer:
(3) SO4^2−, NO3−, S