Define aerenchyma.

Explanation

### Step-by-Step Solution:

1. **Definition of Aerenchyma**: Aerenchyma is a specialized type of parenchyma tissue found in some plants, particularly aquatic plants.

2. **Characteristics of Aerenchyma**:
- It is a modified form of parenchyma, which is a simple plant tissue composed of similar types of cells.
- The cells in aerenchyma are arranged with large intercellular spaces, which form air chambers.

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