In plant cells the vacuoles can occupy upto 90% of the volume of the cell

Answer

### Step-by-Step Solution

1. **Understanding Vacuoles in Plant Cells**:
- In plant cells, vacuoles are large, membrane-bound organelles that can occupy a significant portion of the cell's volume, sometimes up to 90%.

2. **Structure of Vacuoles**:
- Vacuoles are surrounded by a membrane known as the **tonoplast**. This membrane is crucial for maintaining the internal environment of the vacuole.

3. **Contents of Vacuoles**:
- The vacuole contains a liquid known as **cell sap**, which is primarily composed of water, but also includes various substances such as nutrients, waste products, and other materials that the plant may not need.

4. **Function of Vacuoles**:
- The primary functions of vacuoles include:
- **Storage**: They store nutrients and waste products.
- **Regulation of Turgor Pressure**: By maintaining high internal pressure, vacuoles help keep the plant cell turgid, which is important for maintaining the structure of the plant.
- **Excretion**: They act as a storage site for waste materials that are not useful for the plant.

5. **Movement of Materials**:
- The tonoplast facilitates the movement of ions and other substances into the vacuole against their concentration gradient. This means that the concentration of certain ions can be higher in the vacuole than in the cytoplasm, which is essential for various cellular processes.

6. **Conclusion**:
- The ability of vacuoles to occupy up to 90% of the cell volume is a key feature of plant cells, allowing them to store essential substances, manage waste, and maintain turgor pressure, which is vital for plant health and structure.