Which of the cells are the ones that actually develop into the embryo?
A. Trophoblast
B. Inner cell mass
C. Extraembryonic membrane
D. Endoderm

Options

A. A, B
B. A, B, C
C. Only B
D. A, B, C, D

Answer

To determine which cells develop into the embryo, we need to analyze the options provided:

1. **Understanding the Development Process**:
- The process begins with fertilization, forming a zygote.
- The zygote undergoes cleavage, leading to the formation of a morula.
- The morula then develops into a blastula, which in humans is referred to as a blastocyst.

2. **Identifying the Structure of the Blastocyst**:
- The blastocyst has a hollow structure with an outer layer and an inner cell mass.
- The outer layer is composed of cells known as trophoblasts, which are responsible for providing nutrients and forming parts of the placenta.

3. **Focusing on the Inner Cell Mass**:
- Inside the blastocyst, there is a cluster of cells called the inner cell mass.
- It is crucial to note that the inner cell mass is the part that actually develops into the embryo.

4. **Evaluating the Options**:
- **A. Trophoblast**: This layer provides support and nutrients but does not develop into the embryo.
- **B. Inner Cell Mass**: This is the correct answer as it develops into the embryo.
- **C. Extraembryonic Membrane**: These membranes support the embryo but do not form it.
- **D. Endoderm**: This is one of the germ layers that will form part of the embryo but is not a cell type that develops directly into the embryo.

5. **Conclusion**:
- The cells that actually develop into the embryo are the cells of the inner cell mass.

Thus, the correct answer is **B. Inner Cell Mass**.

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