In frustule

Options

A. Epivalve is younger and larger
B. Hypovalve is younger and larger
C. Hypovalve is older and larger
D. Hypovalve is younger and smaller

Answer

### Step-by-Step Solution:

1. **Understanding Frustule**:
- The frustule is the hard and porous cell wall of diatoms. It serves as an external protective layer.

2. **Composition of Frustule**:
- The frustule is primarily composed of silica (SiO2), which is derived from silicic acid. It may also have a layer of organic substances.

3. **Structure of Frustule**:
- The frustule consists of two main parts known as valves:
- **Epivalv (or Epitheca)**: This is the larger valve.
- **Hypovalv (or Hypotheca)**: This is the smaller valve.

4. **Age and Size Relationship**:
- In terms of age and size, the epivalv is typically considered younger and larger, while the hypovalv is older and smaller.

5. **Analyzing the Options**:
- The options provided are:
- A) Epivalv is younger and larger.
- B) Hypovalv is younger and larger.
- C) Hypovalv is older and larger.
- D) Hypovalv is younger and smaller.
- Based on the information, the correct option is A: Epivalv is younger and larger.

### Final Answer:
The correct option is A) Epivalv is younger and larger.