Which of the following primary products of carbon fixation are the 4 carbon compounds in \(C_4\) plants?
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The Hatch-Slack pathway is also known as the \(C_4\) dicarboxylic acid pathway because its first stable intermediates are 4-carbon dicarboxylic acids, specifically malic acid and aspartic acid.
Step 1: Understanding the Concept:
\(C_4\) plants utilize a highly efficient carbon fixation pathway (Hatch-Slack pathway) designed to concentrate carbon dioxide around RuBisCO to suppress photorespiration. Step 3: Detailed Explanation:
1. In the mesophyll cells of \(C_4\) plants, \(\text{CO}_2\) is initially fixed by PEP carboxylase, yielding the unstable 4-carbon compound Oxaloacetate (OAA).
2. OAA is quickly converted into other stable 4-carbon organic acids:
- Malic acid (by malate dehydrogenase)
- Aspartic acid (by aspartate aminotransferase)
3. These 4-carbon compounds are then transported into the adjacent bundle sheath cells, where they are decarboxylated to release \(\text{CO}_2\) directly into the Calvin cycle.
Tartaric acid is not part of this photosynthetic pathway.
Thus, the primary stable 4-carbon products of carbon fixation are malic acid and aspartic acid. Step 4: Final Answer:
The correct option is 1, which corresponds to Malic acid and aspartic acid.
