Question

Give scientific reasons :
(i) Sometimes higher plants and animals too perform anaerobic respiration.

Hint:

Key signs of anaerobic respiration: rapid ATP production under low O2, regeneration of NAD+ via fermentation, and accumulation of lactic acid (animals) or ethanol (plants).

Answer 1

Anaerobic respiration occurs in higher plants and animals when oxygen supply to cells is insufficient for aerobic respiration, or when ATP demand temporarily exceeds the rate at which oxygen can be delivered. In animal muscle cells during intense exercise, oxygen delivery to muscle fibres becomes limiting, so pyruvate from glycolysis is reduced to lactic acid to regenerate NAD+, allowing glycolysis to continue and produce a small amount of ATP rapidly; this process is called lactic acid fermentation. In higher plants, waterlogged or compacted soils restrict O2 availability to roots, so some plant tissues switch to anaerobic pathways where pyruvate is converted to ethanol and carbon dioxide (alcoholic fermentation) to regenerate NAD+ and sustain ATP production at low yield. Physiological consequences and adaptive value: anaerobic respiration yields much less ATP per glucose molecule than aerobic respiration, causes accumulation of by-products (lactic acid in animals, ethanol in plants) that can be toxic if persistent, and must be followed by recovery (oxygen repayment and removal or metabolism of by-products). Despite its low efficiency, anaerobic respiration provides a rapid short-term ATP supply that enables survival and continued function under hypoxic conditions or during bursts of high energy demand.