What is the nature of cell-walls in diatoms?

Explanation

### Step-by-Step Solution:

1. **Identify the Organism**: Diatoms are a type of algae, specifically classified as microalgae. They are commonly found in aquatic environments such as oceans, waterways, and even in soil.

**Hint**: Remember that diatoms belong to the broader category of algae.

2. **Understand the Structure**: Diatoms have a unique outer protective layer known as the cell wall. In the case of diatoms, this cell wall is specifically referred to as the frustule.

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