Xylem is made up of tracheids and vessel elements. Tracheids and vessel elements help plants in being upright against gravity. Which-factor explains the above function of tracheids?

Options

A. Water pressure
B. Chemical composition
C. Tracheids are dead tissues ...
D. Tracheids consist of phloem

Answer

### Step-by-Step Solution:

1. **Understanding Xylem Structure**:
- Xylem is composed of various elements, primarily tracheids and vessel elements, which are crucial for water transport in plants.

2. **Function of Tracheids and Vessel Elements**:
- These components of xylem are responsible for transporting water from the roots to the rest of the plant. This transport is essential for maintaining the plant's structure and helping it stand upright against gravity.

3. **Mechanism of Water Transport**:
- Water enters the roots through osmosis, driven by the concentration of minerals in the soil. When minerals are absorbed into the root, they create a higher osmotic pressure inside the root.

4. **Osmotic Pressure**:
- The increase in osmotic pressure causes water to flow into the roots to balance the concentration gradient. This influx of water creates a pressure that pushes water upward through the tracheids and vessels.

5. **Role of Water Pressure**:
- The upward movement of water through the xylem is primarily due to water pressure, which is generated by the osmotic pressure in the roots and the cohesive properties of water molecules.

6. **Conclusion**:
- Therefore, the factor that explains how tracheids help plants remain upright against gravity is **water pressure**.