Question

During strenuous exercise, glucose is converted into -
(a)Glycogen
(b)Pyruvic acid
(c)Starch
(d)Lactic acid

Answer 1

During strenuous exercise, we tend to breathe harder and faster, and thus we cannot inhale oxygen as efficiently as during resting, thus depriving the cells in our body of oxygen. These cells will undergo a form of respiration that occurs in the absence of a lower level of oxygen. Glucose can form molecules of alcohol or acids under various circumstances.

Complete answer:
- When we do strenuous exercise, the muscle cells of our body are deprived of oxygen as the rate at which we are using and require energy is not enough to the rate being produced by the cells. Hence, the muscle cells undergo anaerobic respiration where the energy produced is much lower compared to aerobic respiration.
- Here, the pyruvate obtained from glucose is converted into lactic acid.
- Lactic dehydrogenase enzyme is responsible for the interconversion of pyruvate and lactate.

Additional Information: - Glucose is converted into glycogen through the process of glycogenesis in the presence of insulin. When a high blood glucose level is detected, insulin helps in converting free glucose back into glycogen.
- Glucose is converted into pyruvic acid at the end of glycolysis, the first step of both aerobic and anaerobic respiration.
- Glucose is converted into starch and stored in plants to provide food and stored energy for them.

So, the correct answer is ‘lactic acid’.

Note: - The equation of conversion of glucose to lactic acid is -
${ C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 }\overset { 2ADP\quad +\quad 2{ P }_{ i }\rightarrow \quad 2ATP\quad +\quad 2{ H }_{ 2 }O\quad }{ \rightarrow } 2{ C }_{ 3 }{ H }_{ 6 }{ O }_{ 3 }$
- Lactic acid fermentation of glucose is of two types - Homolactic fermentation, where one molecule of glucose yields only two molecules of lactic acid, and heterolactic fermentation where one molecule of glucose yields carbon dioxide and ethanol in addition to lactic acid.
- Lactic acid formation in muscle cells was previously believed to cause muscle cramps after heavy exercise.