What is a plasmid?

Explanation

### Step-by-Step Solution:

1. **Definition of Plasmid**: A plasmid is defined as an extra-chromosomal DNA molecule that is distinct from the chromosomal DNA found in prokaryotic cells.

2. **Structure of Plasmids**: Plasmids are typically small, circular, double-stranded DNA molecules. They are separate from the main bacterial DNA, which is usually organized in a region called the nucleoid.

3. **Location**: While plasmids are primarily found in prokaryotic cells (like bacteria), they can also be present in some eukaryotic organisms.

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