Question

Why Does C₄ Photosynthesis Require More ATP?

Answer 1

The C₄ pathway

1. In 1966, Hatch and Slack discovered the C4 cycle, hence the name.
2. The 4-carbon oxaloacetic acid is the first stable compound of the Hatch and Slack cycle, hence is called the C4 cycle.
3. The C₄ pathway is viewed as more efficient than the C₃ pathway.
4. It is on the grounds that it comprises extra steps when contrasted with the C₃ pathway.
5. In the C₄ pathway, carbon dioxide is first fixed in the mesophyll cells to enable the formation of oxaloacetic acid (OAA).
6. Here phosphoenolpyruvate (PEP) acts as an essential/primary CO₂ acceptor.
7. C₄ gets moved to the bundle sheath cells and is decarboxylated to create CO₂ and the 3-carbon compound (pyruvate).
8. The CO₂ enters the C₃ cycle and the 3-carbon compound is shipped back to the mesophyll cells to recover PEP.
9. This extra step requires more energy as ATP.