Which of these microorganisms is made up of only one cell?

Options

A. Spirogyra
B. Rhizopus
C. Agaricus
D. Yeast

Answer

To determine which of the listed microorganisms is made up of only one cell, we can analyze each option provided:

1. **Spirogyra**: This is an example of green algae. It is a multicellular organism, meaning it is made up of many cells. Therefore, this option is not correct.

2. **Rhizopus**: Commonly known as bread mold, this is a type of fungus. Rhizopus is also a multicellular organism. Hence, this option is incorrect as well.

3. **Agaricus**: This is a genus of mushrooms, which are also fungi. Agaricus includes both edible and poisonous species, and like the previous two, it is multicellular. Thus, this option is not correct.

4. **Yeast**: Yeast is a type of fungus that is unicellular. It belongs to the Ascomycetes class and is commonly used in baking and brewing. This option is correct as it is made up of only one cell.

**Conclusion**: The microorganism made up of only one cell is **Yeast**.