Differentiate a tergum and a sternum.

Explanation

### Step-by-Step Solution:

1. **Definition of Tergum**:
- Tergum refers to the dorsal (upper) surface of an insect's body. It is part of the exoskeleton and is made up of sclerites, which are hardened plates composed primarily of chitin.

2. **Definition of Sternum**:
- Sternum, on the other hand, is the ventral (lower) surface of an insect's body. Like the tergum, it is also part of the exoskeleton and consists of sclerites made of chitin.

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