Question

In anaerobic respiration, from one glucose molecule how many net ATP molecules are formed?
A. 2
B. 8
C. 6
D. 4

Answer 1

Glycolysis is the breakdown of one glucose molecule. The glycolysis yields only two ATP molecules in both aerobic and anaerobic respiration. In anaerobic respiration, NADH is not converted to ATP.

Complete answer: Cellular respiration is the set of reactions that benefit the organism by producing energy or using energy. They are known as catabolism and anabolism. The source of energy is glucose. The breakdown of glucose is known as glycolysis. Glycolysis takes place in the cytosol of a cell. Glycolysis involves converting glucose into pyruvate in both conditions, aerobic and anaerobic. Glycolysis actually ends up with one pyruvate, four ATP molecules, and two NADH. Two molecules of ATP are used in the process of glycolysis. Thus, the net gain of ATP is 2 ATPs. Glycolysis has two phases: the preparatory phase where ATP is consumed and the payoff phase where the ATP is produced. The steps at which the ATP are produced are:
-1,3-Bisphosphoglycerate to 3-phosphoglycerate
-Phosphoenolpyruvate (PEP) to pyruvate
In aerobic conditions, there is the conversion of NADH to ATP. One NADH gives three molecules of ATP in the electron transfer system. Thus during aerobic respiration, one glucose molecule gives 2+3+3 molecules of ATP in glycolysis only. The pyruvate enters mitochondria and is reduced to carbon dioxide.
In anaerobic conditions, there is no conversion of NADH to ATP. There is lactate production in animals and ethanol plus carbon dioxide in plants. Thus, the ATP molecules produced in anaerobic respiration is 2 ATP.
Hence, the correct answer is option A.

Note: Though glycolysis produced four ATP molecules and two NADH molecules, the net gain is two ATPs only. The ATP net gain is ATP consumed subtracted from the total ATP produced as in anaerobic condition there is no conversion of NADH to ATP.