Read the following and answer the questions :Cells oxidise glucose in the presence of oxygen to obtain energy. This process takes place in three stages and is called aerobic respiration.(a) Name the three stages of aerobic respiration.(b) Where in th…

Answer: (a) Glycolysis, Krebs cycle and electron transfer chain; (b) cytoplasm, mitochondrial matrix, inner membrane of mitochondria; (c) 38 ATP; (d) C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (38 ATP); (e) lactic acid.

(a) and (b)

1. Glycolysis — in the cytoplasm. One glucose molecule is broken into two molecules of pyruvic acid, with a net gain of 2 ATP and 2 NADH₂.
2. Krebs cycle (tricarboxylic acid cycle) — in the matrix of the mitochondria. Pyruvic acid is first changed to acetyl coenzyme A, which is completely oxidised to CO₂, giving NADH₂, FADH₂ and some ATP.
3. Electron transfer chain — on the inner membrane of the mitochondria. NADH₂ and FADH₂ are oxidised, oxygen accepts the electrons and hydrogen to form water, and most of the ATP is formed here.

(c) Complete oxidation of one glucose molecule gives 38 ATP molecules.

(d) C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (38 ATP)

(e) During heavy exercise the muscles do not get enough oxygen, so glucose is broken down only up to lactic acid. Lactic acid collects in the muscles and causes fatigue and pain.