Question

The given figure shows the diagramatic representation of the Hatch & Slack pathway few labelling are marked as $P,Q$ and $R$

Which of the following option shows the correct labeling of $P,Q,$ and $R$ ?

• A. P - $C_3$ acid , Q - Reduction, R - $C_4$ acid
• B. P - Fixation, Q - $C_4$ acid, R - Regeneration
• C. P - $C_4$ acid, Q - Decarboxylation, R - $C_3$ acid
• D. P - Carboxylation, Q - $C_3$ acid , R - Reduction

Answer 1

Answer: (C)

In the given diagrammatic representation of Hatch and Slack pathway (also known as $C_4$ pathway), the steps marked as $P,Q$ and $R$ are respectively $C_4$ acids, decarboxylation and $C_3$ acids. It is a metabolic cycle involved in the non-light-requiring phase of photosynthesis in certain plants having specific metabolic and anatomical modifications in their mesophyll and bundle sheath cells which facilitate the temporary fixation of carbon dioxide $\left(C{O}_2\right)$ into four-carbon organic acid. These acids are then broken down to three-carbon organic acids along with $C{O}_2$ in bundle sheath cells, where this freed $C{O}_2$ is then fixed into carbohydrates in a normal Calvin cycle pathway.