What is a tonoplast ?

Options

A. Outer membrane of mitochondria
B. Inner membrane of chloroplast
C. Membrane boundry of the vacuole of plant cells
D. Cell membrane of a plant cell

Explanation

### Step-by-Step Solution

1. **Definition of Tonoplast**:
- The tonoplast is a single membrane that surrounds the vacuole in plant cells.

2. **Function of Tonoplast**:
- It acts as a barrier that separates the cytoplasm of the cell from the interior of the vacuole. This separation is crucial for maintaining the cell's internal environment.

3. **Location in Plant Cells**:
- The vacuole, which is surrounded by the tonoplast, occupies a significant amount of space within the plant cell. This is important for storage and maintaining turgor pressure.

4. **Etymology of the Term**:
- The term "tonoplast" is derived from a Greek word meaning "tension" or "stretching." This is because the tonoplast helps maintain tension within the vacuole.

5. **Presence in Cells**:
- The tonoplast is specifically found in plant cells and is absent in animal cells. This distinction is important for understanding the differences between plant and animal cell structures.

6. **Correct Option**:
- Among the given options, the correct answer is that the tonoplast is the membrane boundary of the vacuole of plant cells.