Assertion : Chemical messengers are received at the binding sites of receptor proteins.
Reason : Chemical messenger gives messages to the cell without entering the cell.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion .
B. If both assertion and reason are true but reason is not the correct explanation of assertion .
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Chemical messengers are received at the binding sites of receptor proteins."
- This is true because receptor proteins are located on the cell membrane and are specifically designed to bind with chemical messengers (like hormones or neurotransmitters) that signal the cell to perform certain functions.

2. **Understanding the Reason**:
- The reason states that "Chemical messengers give messages to the cell without entering the cell."
- This is also true. Chemical messengers can bind to the receptors on the cell surface and initiate a response within the cell without needing to enter the cell itself.

3. **Relationship Between Assertion and Reason**:
- The reason explains how the assertion is valid. The chemical messengers interact with the receptor proteins at the binding sites, and this interaction is sufficient to convey the message to the cell without the messengers needing to penetrate the cell membrane.

4. **Conclusion**:
- Since both the assertion and reason are correct, and the reason supports the assertion, we can conclude that the correct answer is that both the assertion and reason are true, and the reason explains the assertion.

### Final Answer:
Both the assertion and reason are correct, and the reason explains the assertion.

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