Question

During strenuous exercise, which of the following changes occur?
A) Glucose is converted into glycogen
B) Glucose is converted into Pyruvic acid
C) Starch is converted into glucose.
D) Pyruvic acid is converted into lactic acid

Answer 1

Hint: In certain animal cells such as muscle cells or myocytes, two types of respiratory processes occur. Aerobic respiration is the most common pathway and occurs in normal conditions in the presence of oxygen. On the other hand under the conditions where oxygen is low in supply or absent the pathway taken is of anaerobic respiration. The end products of aerobic and anaerobic respiration processes are different.

Complete answer:
During strenuous exercise, the oxygen supply to the skeletal muscles decreases. Thus the cells take up an anaerobic respiration pathway for energy production. During anaerobic respiration, glucose, which is the stored food material in the cells, forms Pyruvate during glycolysis and further gets broken down into lactic acid and energy. In contrast to aerobic respiration, the amount of ATP produced in the process is less. After some time this lactic acid is produced to build up in the cells. Thus during strenuous exercise, pyruvic acid is converted into lactic acid.

Considering the other given options:
- The process of conversion of glucose into glycogen is known as glycogenesis. It is the process by which glucose produced after intake of food is converted into glycogen which is the reserved food material by the liver. Thus it is not the right option.
- Glucose gets converted into pyruvic acid is the common step in both aerobic and anaerobic respiration. And the process is known as Glycolysis. Thus it is not the right option.
- Conversion of starch into glucose occurs with the help of an enzyme called Amylase present in different parts of the human digestive system. Thus it is not the right option.

Therefore, the most appropriate answer is option D. That is, during strenuous exercise, pyruvic acid is converted into lactic acid.

Note: Aerobic respiration is also known as TCA or citric acid cycle. The pyruvic acid produced as a result of glycolysis gets converted into citric acid. The end products formed are ATP, water and carbon dioxide as end products.