Question

The first step in respiration is
A. Anaerobic oxidation of pyruvic acid
B. Liberation of carbon dioxide
C. Glycolysis
D. Electron transport system

Answer 1

We know that the process of producing energy by breaking down complex carbohydrates inside the cell is called respiration. As it happens inside the cell, it is also called cellular respiration. The energy produced in cellular respiration is stored in the form of ATP.

Complete answer:
Plants prepare food by using solar energy, water and oxygen. This process happens in the leaves in a green coloured pigment called chlorophyll and is called photosynthesis. The food is produced in the form of glucose and is used to make energy by cellular respiration. The first step involved in the respiration is glycolysis. It occurs in the cytoplasm of a cell. In this process, oxygen is not required. Glucose which is formed by photosynthesis is partially oxidised to produce two molecules of pyruvic acid. Glycolysis is also called the EMP pathway and it is seen in almost all living organisms. In this process, energy molecules such as ATP and NADH are produced. The NADH produced enters the “Electron transport chain” later giving rise to more ATP molecules. Pyruvic acid is formed as a product of glycolysis. The tricarboxylic acid cycle is the second cycle that is involved in cellular respiration. It produces more ATP than glycolysis.
Hence, the correct answer is option C.

Note: Pyruvic acid produced by glycolysis can also enter the process of anaerobic respiration. This process does not require oxygen and the pyruvic acid is either converted into ethanol and carbon dioxide or lactic acid. These steps are called alcohol fermentation and lactic acid fermentation respectively.