Which statement regarding cycling flow of electrons during light reactions is false

Options

A. The process takes place in stromal lamella
B. ATP synthesis takes place
C. `NADP + H^(+)` is synthesised
D. Takes place only when light of wavelength beyond 680 nm is available for excitation.

Answer

To determine which statement regarding the cyclic flow of electrons during light reactions is false, we need to analyze the characteristics of the cyclic electron flow in photosynthesis. Here’s a step-by-step breakdown:

### Step 1: Understand the Process of Cyclic Electron Flow
Cyclic electron flow occurs in the thylakoid membranes of chloroplasts, specifically involving Photosystem I (PSI). When light energy is absorbed by PSI, it excites electrons.

**Hint:** Focus on the role of Photosystem I in the cyclic flow of electrons.

### Step 2: Identify the Components Involved
In cyclic electron flow, the excited electrons from PSI are transferred to an electron transport chain (ETC) and eventually return to PSI. This process does not involve Photosystem II (PSII) and does not produce NADPH.

**Hint:** Remember that cyclic flow involves only PSI and does not lead to the production of NADPH.

### Step 3: Analyze the Role of ATP and NADPH
During cyclic electron flow, ATP is produced through photophosphorylation, but NADPH is not synthesized because the enzyme NADP reductase is absent in this pathway.

**Hint:** Consider what products are generated in cyclic flow versus non-cyclic flow.

### Step 4: Evaluate the Statements
Now, let’s evaluate the statements regarding cyclic electron flow:
1. The process occurs in the stromal lamellae.
2. ATP synthesis occurs due to the presence of ATP synthase.
3. NADP reductase is present, allowing for NADPH synthesis.
4. The process takes place only when wavelengths beyond 680 nm are available for excitation.

**Hint:** Identify which statement contradicts the known facts about cyclic electron flow.

### Step 5: Identify the False Statement
From the analysis:
- Statement 1 is true: Cyclic flow occurs in the stromal lamellae.
- Statement 2 is true: ATP synthesis occurs.
- Statement 3 is false: NADP reductase is absent, so NADPH is not synthesized.
- Statement 4 is true: Cyclic flow requires light wavelengths beyond 680 nm.

Thus, the false statement is **option number 3**: "NADP reductase is present, allowing for NADPH synthesis."

**Final Answer:** The false statement regarding the cyclic flow of electrons during light reactions is option number 3.