When microorganisms are made up of just one cell, they are called ________.

Options

A. unicellular
B. multicellular
C. both
D. none of these

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the term used to describe microorganisms that consist of only one cell.

2. **Defining Microorganisms**: Microorganisms are very small organisms that cannot be seen with the naked eye and can only be observed under a microscope.

3. **Types of Microorganisms**: Microorganisms can be classified into two main types based on the number of cells they have:
- **Unicellular**: This term refers to organisms that are made up of a single cell. The prefix "uni-" means one.
- **Multicellular**: This term refers to organisms that are composed of more than one cell. The prefix "multi-" means many.

4. **Identifying the Correct Term**: Since the question specifically asks for microorganisms that are made up of just one cell, the correct term is "unicellular".

5. **Examples**: An example of a unicellular microorganism is amoeba. In contrast, humans are an example of multicellular organisms.

6. **Final Answer**: Therefore, the answer to the question is "unicellular".

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