CBSE Class 11 Biology Chapter 14: Respiration in Plants NCERT Solutions

Solution: The differences between the given pairs are as follows:

1. Respiration vs. Combustion

   Respiration is a biochemical process that occurs within living cells under biological control, requiring enzymes, and producing ATP. In contrast, combustion is a physiochemical process that occurs outside living cells, is uncontrolled, does not require enzymes, and does not generate ATP.

   Respiration	Combustion
   1. It is a biochemical process.	1. It is a physiochemical process.
   2. It occurs in the living cells.	2. It does not occur in the living cells.
   3. ATP is generated.	3. ATP is not generated.
   4. Enzymes are required.	4. Enzymes are not required.
   5. It is a biologically-controlled process.	5. It is an uncontrolled process.

2. Glycolysis vs. Krebs' cycle

   Glycolysis is the initial breakdown of glucose into pyruvic acid, occurring in the cytoplasm and forming a linear pathway. The Krebs' cycle (or citric acid cycle) is a cyclic pathway that occurs in the mitochondrial matrix, further oxidizing acetyl-CoA to release energy.

   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 and anaerobic respiration.	3. It occurs only in aerobic respiration.
   4. It generates 2 NADH2 and a net of 2 ATP molecules on the breakdown of one glucose molecule.	4. It produces 6 NADH2, 2 FADH2, and 2 ATP molecules on the breakdown of two acetyl-CoA molecules.

3. Aerobic respiration vs. Fermentation

   Aerobic respiration requires oxygen and leads to the complete oxidation of the respiratory substrate, producing a large amount of ATP. Fermentation occurs in the absence of oxygen, results in incomplete oxidation, and yields a small amount of ATP.

   Aerobic respiration	Fermentation
   1. Oxygen is used for deriving energy.	1. Occurs in the absence of oxygen.
   2. Occurs in the mitochondria.	2. Occurs in the cytoplasm.
   3. End products are carbon dioxide and water.	3. End products are ethyl alcohol and carbon dioxide (in alcoholic fermentation).
   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.

Solution: Respiratory substrates are the organic compounds that are oxidized during the process of cellular respiration to release energy. These substrates are broken down through a series of biochemical reactions. The most common respiratory substrate is carbohydrates, particularly glucose. However, fats, proteins, and organic acids can also serve as respiratory substrates depending on the organism and its metabolic state.

Solution: Glycolysis is the first stage of cellular respiration, where one molecule of glucose (a 6-carbon sugar) is broken down into two molecules of pyruvic acid (a 3-carbon compound). This process occurs in the cytoplasm and involves a series of ten enzymatic reactions. It yields a net production of 2 ATP molecules and 2 NADH molecules.

The schematic representation is as follows:

Glucose (6C) $\xrightarrow{ATP}$ Glucose-6-phosphate (6C)

Glucose-6-phosphate (6C) $\xrightarrow{}$ Fructose-6-phosphate (6C)

Fructose-6-phosphate (6C) $\xrightarrow{ATP \rightarrow ADP}$ Fructose 1,6-bisphosphate (6C)

Fructose 1,6-bisphosphate (6C) $\xrightarrow{}$ 2 $\times$ Triose phosphate (3C) (Glyceraldehyde-3-phosphate and Dihydroxyacetone phosphate)

2 $\times$ Triose phosphate (3C) $\xrightarrow{NAD^+ \rightarrow NADH+H^+}$ 2 $\times$ 1,3-bisphosphoglyceric acid (3C)

2 $\times$ 1,3-bisphosphoglyceric acid (3C) $\xrightarrow{ADP \rightarrow ATP}$ 2 $\times$ 3-phosphoglyceric acid (3C)

2 $\times$ 3-phosphoglyceric acid (3C) $\xrightarrow{}$ 2 $\times$ 2-phosphoglycerate (3C)

2 $\times$ 2-phosphoglycerate (3C) $\xrightarrow{}$ 2 $\times$ Phosphoenolpyruvate (PEP) (3C)

2 $\times$ Phosphoenolpyruvate (PEP) (3C) $\xrightarrow{ADP \rightarrow ATP}$ 2 $\times$ Pyruvic acid (3C)