The blastomeres in the blastocyst are arranged into an outer layer `____A____` and inner group of cells attached to trophoblast called the `___B____`.

Options

A. A is trophoblast and B are inner cell mass
B. A are inner cell mass and B is trophoblast
C. Both are trophoblast
D. Both are inner cell masses

Answer

To solve the question regarding the arrangement of blastomeres in the blastocyst, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Blastocyst Structure**:
- The blastocyst is a structure formed in the early stages of embryonic development. It consists of a hollow ball of cells known as blastomeres.

2. **Identifying the Layers**:
- The blastomeres are organized into two main components: an outer layer and an inner group of cells.

3. **Outer Layer**:
- The outer layer of the blastocyst is known as the **trophoblast**. This layer plays a crucial role in implantation into the uterine wall and contributes to the formation of the placenta.

4. **Inner Group of Cells**:
- The inner group of cells that are attached to the trophoblast is referred to as the **inner cell mass** (ICM). This group of cells will eventually develop into the embryo itself.

5. **Filling in the Blanks**:
- Therefore, for the blanks in the question:
- A = **trophoblast**
- B = **inner cell mass**

### Final Answer:
The blastomeres in the blastocyst are arranged into an outer layer **trophoblast** (A) and an inner group of cells attached to the trophoblast called the **inner cell mass** (B).

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