Which one is not formed from ectoderm?

Options

A. Notochord
B. Epidermis
C. Internal ear
D. Branchial arches.

Answer

To determine which option is not formed from ectoderm, we can follow these steps:

### Step 1: Understand the Germ Layers
The human body develops from three primary germ layers during embryonic development: ectoderm, mesoderm, and endoderm. Each layer gives rise to different tissues and organs.

### Step 2: Identify the Ectoderm Derivatives
The ectoderm is the outermost layer and is responsible for forming:
- The epidermis (the outer layer of skin)
- The nervous system (including the brain and spinal cord)
- Sensory organs (like eyes and ears)

### Step 3: Analyze the Options
Now, let's analyze the options provided:
- **A. Notochord**: This is a flexible rod-like structure that serves as a primary axial support in the early embryo and is derived from the mesoderm.
- **B. Epidermis**: This is derived from the ectoderm.
- **C. Internal Ear**: This structure is also derived from the ectoderm.

### Step 4: Conclusion
Since the notochord is derived from the mesoderm and not the ectoderm, the correct answer to the question "Which one is not formed from ectoderm?" is option A, the notochord.

### Final Answer
**Option A: Notochord**

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