Distinguish between anaerobic pathways in eukaryotes (e. g. yeasts) and anaerobic respiration in anaerobic microbes

Anaerobic respiration refers to the break down of food (sugar) in absence of oxygen in order to produce energy (ATP or adenosine triphosphate).

In yeast, alcoholic fermentation takes place by which glucose is converted into ethanol (alcohol), carbon dioxide (CO₂), and energy (ATP). It helps in regeneration of NAD⁺ lost during glycolysis. No electron transport chain is required in this process.

The overall reaction can be written as:

Glucose → Pyruvate → Ethanol + Carbon dioxide + ATP.

Contrary, in anaerobic bacteria respiration takes place by using electron acceptor other than oxygen such as sulfate, nitrate, sulfur, fumarate etc. Hence, electrons are passed through a electron transport chain which are finally accepted by any molecule other than oxygen.

Other molecules have less oxidizing potential as compared to the oxygen and thus less energy is released per oxidizing molecule. It makes the anaerobic respiration less efficient as compared to the aerobic respiration.

Examples of anaerobic microbes are methanogens (Methanosarcina barkeri uses CO₂ as final electron acceptor),  Desulfuromonadales (uses sulfur as final electron acceptor) etc.

sulfur dioxide

explanation: acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. these substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.