Question

$C_4$ plants are more efficient in photosynthesis than $C_3$ plants due to

• A. higher leaf area
• B. presence of larger number of chloroplasts in the leaf cells
• C. presence of thin cuticle
• D. lower rate of photorespiration.

Answer 1

Answer: (D)

Rate of net photosynthesis in $C_3$ plants is 15-35 mg $CO/d{m}^2$ /hr while in $C_4$ plants it 40-80 mg CO,/ $d{m}^2$/hr. This variation in rate is due to photorespiration. Photorespiration is an inhibitory process which decreases the rate of photosynthesis. In excess of oxygen RUBP carboxylase converts to RuBP oxygenase. As a result glycolate synthesis is enhanced and leads to begin photorespiration. Photorespiration is negligible or absent in $C_4$ plants and present only in $C_3$ plants. So $C_4$ plants are photosynthetically more efficient.