Question

The ratio of the number of electrons to be excited from PS II during non-cyclic photophosphorylation and PS I during cyclic phosphorylation respectively to form 120 ATPs

• A. 2:3
• B. 1:4
• C. 4:5
• D. 3:4

Hint:

Understanding the electron transport chain's role in energy conversion in photosynthesis can clarify how plants convert light energy into chemical energy.

Answer 1

The Correct Option is A

Step 1: In non-cyclic photophosphorylation, electrons are excited in PS II (Photosystem II), where water molecules are split, releasing oxygen and electrons. These excited electrons are passed along the electron transport chain and used to generate ATPs through chemiosmosis. For every two electrons excited from PS II, 3 ATP molecules are produced in the process. 
Step 2: In cyclic phosphorylation, electrons are excited in PS I (Photosystem I), but instead of being passed to NADP+ to form NADPH, they are returned to the electron transport chain. This cycle generates additional ATPs but does not contribute to the production of NADPH. For every two electrons excited from PS I during cyclic phosphorylation, 2 ATP molecules are produced. 
Step 3: To form 120 ATPs, the ratio of electrons excited from PS II during non-cyclic phosphorylation to those excited from PS I during cyclic phosphorylation is 2:3. This ratio is essential for maintaining the balance between ATP and NADPH production during the light reactions of photosynthesis. 
Conclusion: The correct ratio of electrons excited from PS II (non-cyclic) to PS I (cyclic) to form 120 ATPs is 2:3.