NCERT Solutions for Class 11 Biology Chapter 12 Respiration in Plants

Short Note:

• Glycolysis (the common pathway in both aerobic and anaerobic respiration) occurs in the cytoplasm, breaking down one molecule of glucose into two molecules of pyruvate, with a net gain of 2 ATP and 2 NADH.

Short Note:

• In the absence of oxygen, pyruvate undergoes fermentation: converted to ethanol + CO2 (alcoholic fermentation, e.g. in yeast) or to lactic acid (lactic acid fermentation, e.g. in muscle cells), regenerating NAD+ needed to sustain glycolysis.

Short Note:

• In the presence of O2, pyruvate enters the mitochondria and is converted to Acetyl CoA, which enters the Krebs Cycle (Citric Acid Cycle) in the mitochondrial matrix, generating NADH, FADH2, ATP, and releasing CO2.

• NADH and FADH2 then feed electrons into the Electron Transport System (ETS) on the inner mitochondrial membrane, generating a large amount of ATP via oxidative phosphorylation, with O2 as the final electron acceptor (forming water).

Short Note:

• The complete aerobic oxidation of one glucose molecule theoretically yields a maximum of about 36-38 ATP molecules (through glycolysis, Krebs cycle, and ETS combined), although actual yield varies due to factors like transport costs across membranes.