Why the receptors embedded in cell membranes show selectivity for one chemical messenger over the other ?

Explanation

### Step-by-Step Solution:

1. **Understanding Receptors**: Receptors are specialized proteins embedded in cell membranes that respond to specific chemical messengers (like hormones or neurotransmitters).

2. **Key-Lock Principle**: The selectivity of receptors can be explained using the "key-lock" model. In this analogy, the receptor is the lock, and the chemical messenger is the key. Only the correct key (messenger) can fit into the lock (receptor) and activate it.

3. **Specificity of Shape**: Each receptor has a unique shape and structure that corresponds to a specific chemical messenger. This means that only certain messengers can bind to specific receptors, much like a key can only fit into its corresponding lock.

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