Question

Explain the process of cellular respiration.

Answer 1

Cellular Respiration

It is the process by which each cell performs oxidation of organic compound (glucose) and releases energy in the form of ATP (Adenosine triphosphate) in gradual steps. Cellular respiration is of two types:

• Aerobic respiration is the type of respiration that takes place in the presence of oxygen and hence, complete oxidation of organic compounds takes place. This results in the release of a large amount of energy.

$\mathrm{Glucose}\left({\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6\right)+\mathrm{Oxygen}\left(6{\mathrm{O}}_2\right)\to \mathrm{Carbon}\mathrm{dioxide}\left(6{\mathrm{CO}}_2\right)+\mathrm{Water}\left(6{\mathrm{H}}_2\mathrm{O}\right)+38\mathrm{ATP}\left(\mathrm{Energy}\right)$

• Anaerobic respiration is the type of respiration that occurs in the absence of oxygen with incomplete oxidation of glucose. It releases a low amount of energy.

$\mathrm{Glucose}\left({\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6\right)\to \mathrm{Alcohol}\left(2{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\right)+\mathrm{Carbon}\mathrm{dioxide}\left(2{\mathrm{CO}}_2\right)+2\mathrm{ATP}\left(\mathrm{Energy}\right)/\mathrm{Lactic}\mathrm{acid}\left(2{\mathrm{C}}_3{\mathrm{H}}_6{\mathrm{O}}_3\right)+\mathrm{ATP}\left(\mathrm{Energy}\right)$

Process of Aerobic Respiration

Aerobic respiration occurs in the following steps:

1. Glycolysis: It is the first step in respiration. In this step, one molecule of glucose (C₆H₁₂O₆) is broken down into two molecules of pyruvic acid. This step occurs in the cytoplasm.
2. Krebs cycle: In this step, each pyruvic acid molecule is first converted into acetyl Co-A, followed by a series of reactions. This step occurs in the mitochondria.
3. Electron transport system (ETS) and Oxidative phosphorylation: These steps also occur in mitochondria (mitochondrial membrane). ETS is a series of electron carriers through which electrons are passed and along with it, a proton (H⁺) gradient is created across the membrane. The proton gradient energy is used to convert ADP to ATP with the help of ATPase; this is called oxidative phosphorylation.

A total of 38 ATP is created at the end of this process, of which there is a net gain of 36 ATP.

Process of Anaerobic Respiration

Anaerobic respiration takes place in the cytoplasm. Glycolysis is common in both aerobic and anaerobic respiration. However, steps like the Krebs cycle and ETS do not occur in anaerobic respiration. Glycolysis results in the formation of pyruvic acid, which then undergoes reduction. In yeasts, pyruvic acid is converted into Ethyl alcohol, Carbon dioxide and energy. When there is a lack of oxygen in the muscle cells in animals, pyruvic acid converts into lactic acid and energy.