An embryo is made up of a single cell.

Explanation

### Step-by-Step Solution

1. **Understanding the Statement**: The statement claims that "an embryo is made up of a single cell." We need to evaluate whether this statement is true or false.

2. **Definition of an Embryo**: An embryo is the early stage of development in multicellular organisms. It begins its development from a single cell called a zygote.

3. **Formation of the Zygote**: The zygote is formed when a male gamete (sperm) fuses with a female gamete (egg) during the process of fertilization. This fusion creates a diploid cell, which is the zygote.

4. **Characteristics of the Zygote**: The zygote is indeed a unicellular structure, meaning it consists of only one cell at this stage.

5. **Development of the Embryo**: After the formation of the zygote, it undergoes a series of cell divisions known as mitosis. Through these divisions, the single zygote cell divides to form multiple cells.

6. **Transition from Zygote to Embryo**: As the zygote continues to divide and differentiate, it develops into a multicellular structure known as the embryo. This process involves both cell division and cell differentiation.

7. **Conclusion**: Since an embryo is formed from the zygote, which starts as a single cell but eventually becomes a multicellular structure, the original statement "an embryo is made up of a single cell" is false.

### Final Answer
The statement "an embryo is made up of a single cell" is **false**. An embryo is a multicellular structure that develops from a single-celled zygote through cell division.

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