Which of the following is absent in nerve cell?

Options

A. (1) mitrochondria
B. (2) Nissl granules
C. (3) nucleus .
D. (4)Centriole

Answer

To determine which structure is absent in a nerve cell, we need to analyze the options provided:

1. **Mitochondria**: These organelles are responsible for energy production in cells. Nerve cells, like all other cells, require energy to function, so mitochondria are present in nerve cells.

2. **Nissl granules**: These are rough endoplasmic reticulum and ribosomes found in nerve cells, which are involved in protein synthesis. Nissl granules are indeed present in nerve cells.

3. **Nucleus**: The nucleus contains the cell's genetic material and is essential for cell function and regulation. Nerve cells have a nucleus.

4. **Centrioles**: These are cylindrical structures involved in cell division. In mature neurons, centrioles are typically absent because nerve cells do not divide after they have fully matured.

Based on this analysis, the structure that is absent in nerve cells is **centrioles**.

### Step-by-Step Solution:
1. **Identify the structures listed in the options**: Mitochondria, Nissl granules, nucleus, and centrioles.
2. **Evaluate the presence of each structure in nerve cells**:
- Mitochondria: Present for energy production.
- Nissl granules: Present for protein synthesis.
- Nucleus: Present for genetic material and regulation.
- Centrioles: Absent in mature nerve cells.
3. **Conclude which structure is absent**: Since centrioles are not present in mature nerve cells, the answer is centrioles.

### Final Answer:
The structure that is absent in nerve cells is **centrioles** (Option D).