Read the following statements and write the appropriate term against each statement.
I am like a policeman. I do not allow anything and everything to get in and out of the cell. Who am I? ...................

Explanation

To answer the question, we need to identify the term that corresponds to the description given in the statement. Let's break it down step by step:

### Step-by-Step Solution:

1. **Understanding the Statement**: The statement describes something that controls what enters and exits the cell, comparing it to a policeman who regulates access.

2. **Identifying the Function**: The function described is that of a barrier or gatekeeper. In biological terms, this refers to a structure that selectively allows certain substances to pass while blocking others.

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