The embryonic stage with outer layer trophoblast and inner cell mass attached at one region of the trophoblast is

Options

A. Morula
B. Blastula
C. Blastocyst
D. Gastrula

Answer

To solve the question regarding the embryonic stage characterized by an outer layer called the trophoblast and an inner cell mass attached at one region of the trophoblast, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Terminology**:
- The question mentions two key components: the **trophoblast** and the **inner cell mass**. The trophoblast is the outer layer of cells that will eventually contribute to the placenta, while the inner cell mass will develop into the embryo.

2. **Identify the Stages of Embryonic Development**:
- The stages of embryonic development include:
- **Morula**: A solid ball of cells (8-cell stage) that does not have a defined outer layer or inner mass.
- **Blastula**: A stage before the formation of the blastocyst, characterized by a hollow structure but not yet defined as a blastocyst.
- **Blastocyst**: A stage where the inner cell mass is present and attached to the trophoblast, which is the outer layer.

3. **Analyze the Options**:
- **Morula**: Incorrect, as it does not have a trophoblast or inner cell mass structure.
- **Grastula**: Incorrect, as it forms after the morula and is not yet implanted.
- **Blastula**: Incorrect, as it is a stage before the blastocyst.
- **Blastocyst**: Correct, as it has a trophoblast and an inner cell mass that is attached to it.

4. **Conclusion**:
- The embryonic stage described in the question is the **blastocyst**. This is the stage where implantation occurs in the uterus, and it features the outer trophoblast layer and the inner cell mass.

### Final Answer:
The embryonic stage with an outer layer trophoblast and an inner cell mass attached at one region of the trophoblast is the **blastocyst**.

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