List two functions of microtubules.

Explanation

**Step-by-Step Solution:**

1. **Definition of Microtubules**: Microtubules are structural components found in the cytoplasmic matrix of eukaryotic cells. They are hollow, unbranched cylindrical tubes with a diameter of approximately 25 nm.

2. **Composition**: Microtubules are primarily composed of tubulin protein, which is a key building block that forms these cylindrical structures.

3. **Function 1 - Maintaining Cell Shape and Rigidity**: One of the primary functions of microtubules is to help maintain the shape and rigidity of the cell. They provide structural support, ensuring that the cell retains its form and does not collapse.

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