Question

Compared to $C_{3}$ plants, $C_{4}$ plants

• A. concentrate oxygen in cells, thereby overcoming the problem of photorespiration
• B. fix carbon dioxide into a four carbon sugar at night, and then release the carbon dioxide during the day
• C. remove oxygen from the air spaces between cells in the leaves and thereby avoid photorespiration
• D. have adaptations which concentrate carbon dioxide in the photosynthetic cells

Answer 1

Answer: (D)

The C4 pathway is also known as the Hatch and Slack pathway, occurs in the plant that is adapted to dry tropical regions, e.g., Sugarcane, Maize. As compared to the C3 plant, the C4 plants have an adaptation that constantly concentrates carbon dioxide in the photosynthetic cells. It is a cyclic process in which the primary CO₂ acceptor is three-carbon molecule phosphoenolpyruvate which is present in mesophylls cells. PEP carboxylase or PEPcase is the enzyme that catalyzes the CO₂ fixation. In the C4 plants, the mesophyll cells lack the enzyme RuBisCO. The 4-Carbon oxaloacetic acid is formed in the mesophyll cell, which is the first product of this pathway. In the mesophyll cells, the oxaloacetic acid is then converted to other 4-carbon compounds like malic acid or aspartic acid and then it is transported to the bundle sheath cells. To release CO₂ and a 3-carbon molecule in the bundle sheath cells, these C4 acids are broken down, and the CO₂ released in the bundle sheath cells enter the Calvin pathway.