Assertion : Photomorphogenetic responses are controlled by the pigment cytochrome.
Reason :Cytochrome exists in two photoreversible forms

Options

A. (a) If both A and R are true and R is the correct explanation of A
B. (b) If both A and R are true but R is not the correct explanation of A
C. (c) If A is true and R is false
D. (d) If both A and R are false

Answer

To solve the assertion-reason question, we will analyze both the assertion and the reason step by step.

### Step 1: Analyze the Assertion
The assertion states: "Photomorphogenetic responses are controlled by the pigment cytochrome."
- **Evaluation**: This statement is incorrect. Photomorphogenetic responses in plants are primarily controlled by a class of photoreceptors known as phytochromes, not cytochromes. Phytochromes are responsible for detecting light and regulating plant growth and development in response to light signals.

### Step 2: Analyze the Reason
The reason states: "Cytochrome exists in two photoreversible forms."
- **Evaluation**: This statement is also incorrect. Cytochromes are a group of heme-containing proteins that are classified into four types based on the kind of heme they possess: cytochrome a, cytochrome b, cytochrome c, and cytochrome d. They do not exist in just two photoreversible forms; rather, they have distinct types based on their heme structure.

### Step 3: Conclusion
Since both the assertion and the reason are false, we conclude that the correct answer is option D, which states that both the assertion and reason are false.

### Final Answer
Both the assertion and reason are false. Therefore, the correct option is D.

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