Which is not a tissue?

Options

A. Xylem
B. Phloem
C. Collagen
D. Cambium

Explanation

To determine which option is not a tissue, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Options**: We need to look at the options provided in the question. The options include xylem, phloem, collagen, and cambium.

2. **Analyze Xylem and Phloem**:
- Xylem is a type of vascular tissue in plants responsible for the transport of water and minerals from the roots to the rest of the plant.
- Phloem is another type of vascular tissue that transports food (sugars) produced by photosynthesis from the leaves to other parts of the plant.
- Both xylem and phloem are classified as tissues because they are made up of groups of cells that work together to perform a specific function.

3. **Analyze Cambium**:
- Cambium is a type of meristematic tissue found in plants. It is responsible for the growth in thickness of stems and roots by producing new xylem and phloem cells.
- Since cambium is also a collection of cells performing a specific function, it is classified as a tissue.

4. **Analyze Collagen**:
- Collagen is described as an insoluble fibrous protein found in the connective tissues of animals. It provides strength and support to various structures like skin, muscles, and bones.
- However, collagen itself is not a tissue; it is a protein that forms fibers which contribute to the structure of connective tissues.

5. **Conclusion**: Based on the analysis, collagen is not a tissue, while xylem, phloem, and cambium are all classified as tissues.

### Final Answer:
The option that is not a tissue is **collagen**.

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