Question

Given below are some characteristics of photosynthetic plants. Which of these are true for $C_{4}$ plants?
(i) Rubisco is present in the mesophyll cells
(ii) 3-carbons in the primary $CO_{2}$ acceptor
(iii) The primary $CO_{2}$ fixation product is $PGA$
(iv) Possess $PEP$ Case
(v) The initial carboxylation reaction occurs in bundle sheath cells
(vi) The calvin cycle takes place in bundle sheath cells
(vii) $4-$ carbon atoms in the primary $CO_{2}$ fixation product

• A. $\left(\right.i\left.\right),\left(\right.iv\left.\right),\left(\right.v\left.\right),\left(\right.vii\left.\right)$
• B. $\left(\right.i\left.\right),\left(\right.ii\left.\right),\left(\right.iii\left.\right),\left(\right.iv\left.\right),\left(\right.vii\left.\right)$
• C. $\left(\right.ii\left.\right),\left(\right.iii\left.\right),\left(\right.iv\left.\right),\left(\right.vi\left.\right),\left(\right.vii\left.\right)$
• D. $\left(\right.ii\left.\right),\left(\right.iv\left.\right),\left(\right.vi\left.\right),\left(\right.vii\left.\right)$

Answer 1

Answer: (D)

The C_{​​​​​​4} pathway is also known as Hatch and Slack pathway, occurs in the plants that are adapted to dry tropical regions, e.g., Sugarcane, Maize. It is a cyclic process in which the primary CO_{​​​​​2} acceptor is three-carbon molecule phosphoenolpyruvate which is present in mesophylls cells. PEP carboxylase or PEPcase is the enzyme that catalyzes the CO_{​​​​​2} fixation. In the C_{​​​​​​4} 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 CO_​​​2 and a 3-carbon molecule in the bundle sheath cells, these C_{​​​​​4} acids are broken down, and the CO_{​​​​​2} released in the bundle sheath cells enter the Calvin pathway.