(d) : Rate of net photosynthesis in C3 plants is 15−35mg‌CO2∕dm2∕hr while in C4 plants it 40−80mgCO2∕dm2∕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 C4 plants and present only in C3 plants. So C4 plants are photosynthetically more efficient.