Which process also occurs when only light of wavelengths beyond 680 nm are available for excitation?

Options

A. Cyclic photophosphorylation
B. Non-cyclic photophosphoylation
C. Both (1) and (2)
D. None of these

Answer

To answer the question, "Which process also occurs when only light of wavelengths beyond 680 nm are available for excitation?", we need to analyze the types of photophosphorylation involved in photosynthesis.

### Step-by-Step Solution:

1. **Understanding Photophosphorylation**:
- Photophosphorylation is the process of ATP formation using light energy. It occurs in two forms: cyclic and non-cyclic photophosphorylation.

2. **Identifying the Types**:
- **Non-Cyclic Photophosphorylation**: Involves both Photosystem I (PSI) and Photosystem II (PSII). PSII absorbs light at around 680 nm (P680), while PSI absorbs light at around 700 nm (P700).
- **Cyclic Photophosphorylation**: Involves only Photosystem I (PSI). Here, electrons are excited by light and are transported in a cycle, returning to PSI.

3. **Analyzing the Wavelengths**:
- The question specifies light wavelengths beyond 680 nm. This means that only the absorption by Photosystem I (which has a peak absorption at 700 nm) is relevant.

4. **Conclusion**:
- Since only Photosystem I is active when light of wavelengths beyond 680 nm is available, the process that occurs is **Cyclic Photophosphorylation**. Non-cyclic photophosphorylation cannot occur because it requires light at 680 nm, which is not available in this scenario.

5. **Final Answer**:
- The correct answer is **Cyclic Photophosphorylation**.