Question

Which of the following statement(s) is (are) correct?
(i) Pyruvate can be converted into ethanol and carbon dioxide by Yeast.
(ii) Fermentation takes place in aerobic bacteria.
(iii) Fermentation takes place in mitochondria.
(iv) Fermentation is a form of anaerobic respiration.

• A. (i) and (iii)
• B. (ii) and (iv)
• C. (i) and (iv)
• D. (ii) and (iii)

Answer 1

Answer: (C)

(i) and (iv)

Hint: Many bacteria and yeasts carry out fermentation in the absence of oxygen as an alternative way to get sufficient energy to support life processes.

Part 1 - Definition - Anaerobic respiration or fermentation

• Depending upon environmental conditions, individual cells and microbes have the ability to switch between the two different modes of energy production, i.e. aerobic and anaerobic (fermentation).
• Fermentation is the breaking down of sugar molecules into simpler compounds to produce substances that can be used in making chemical energy in the absence of oxygen.
  
• It involves glycolysis, i.e. conversion of glucose into pyruvic acid and conversion of pyruvate into acid or alcohol.

Part 2 - Types of fermentation

• There are three distinct types of fermentation:

Lactic acid fermentation - Pyruvic acid is converted into lactic acid and $C{O}_2$. Example - muscles cells during heavy exercises.

Alcohol fermentation - Yeasts break pyruvate molecules into alcohol and carbon dioxide molecules.

Acetic acid fermentation - Some bacteria like Acetobactor converts pyruvate into acetic acid.

Part 3 - Location

• Anaerobic respiration is divided into two parts: glycolysis and fermentation.
• Both occur in the cytoplasm, not mitochondria.

Part 4 - Conclusion

• Statement (i) is correct as yeast converts pyruvate into ethanol and $C{O}_2$ in anaerobic respiration.
• Statement (ii) is incorrect, as fermentation doesn't take place in aerobic bacteria but in anaerobic bacteria.
• Statement (iii) is also incorrect, as fermentation takes place in cytoplasm instead of mitochondria.
• Statement (iv) is correct as fermentation is a form of anaerobic respiration.

Final step: The correct statements are (i) and (iv).