Question

Differentiate between

(a) Respiration and Combustion

(b) Glycolysis and Kreb's cycle

(c) Aerobic respiration and fermentation

Answer 1

(a)

Respiration	Combustion
1. It takes place in living cells only.	1. It does not take place in the living cell.
2. It is carried out with the help of various enzymes.	2. Enzymes are not involved in this process.
3. The oxidation of food and the liberation of energy occur in a step-wise manner.	3. The substances are oxidized spontaneously with sudden release of energy.
4. It occurs at the body temperature of the organism.	4. Sudden release of energy generates high temperature of a fire.
5. 60% of energy escapes as body heat and 40% of energy is packaged directly into new chemical energy (ATP).	5. Energy released in combustion is dissipated as heat and to some extent as light.

(b)

Glycolysis	Krebs cycle
1. It is a linear pathway.	1. It is a cyclic pathway.
2. It occurs in the cell cytoplasm.	2. It occurs in the mitochondrial matrix.
3. It occurs in both aerobic as well as anaerobic respiration.	3. It occurs in aerobic respiration only.
4. Net generation of 2 $NAD{H}^{+}{H}^{+}$ and 2 ATP molecules occurs on the breakdown of one glucose molecule.	4. It produces 6 $NAD{H}^{+}{H}^{+}$, 2FADH${}_2$, and 2 ATP molecules on the breakdown of two acetyl-CoA molecules generated after glycolysis of one glucose molecule.

(c)

Aerobic respiration	Fermentation
1. Oxygen is used for deriving energy.	1. Occurs in the absence of oxygen.
2. Occurs in the cytoplasm and mitochondria.	2. Occurs in the cytoplasm.
3. End products are carbon dioxide and water.	3. End products are ethyl alcohol and carbon dioxide.
4. Complete oxidation of the respiratory substrate takes place.	4. Incomplete oxidation of the respiratory substrate takes place.
5. About 36 ATP molecules are produced.	5. Only 2 ATP molecules are produced.