The flow of water upward through the xylem in plants can achieve fairly high rates up to 15 m height

The process responsible for the upward movement of water through the xylem in plants is known as transpiration pull. This process utilizes several physical forces to create a continuous flow of water from the roots to the leaves.

Transpiration:
Transpiration is the process by which water is lost from the leaves of plants in the form of water vapor. This loss of water creates a negative pressure or tension in the xylem, which pulls water upward from the roots.

Cohesion-tension theory:
The cohesion-tension theory explains how water molecules are able to move against gravity in the xylem. It is based on two main principles:

1. Cohesion: Water molecules are attracted to each other through hydrogen bonding, creating a cohesive force. This allows water to form a continuous column within the xylem.

2. Transpiration pull: As water evaporates from the leaves, it creates a negative pressure or tension in the xylem. This tension pulls water molecules upward, from the roots to the leaves, through the xylem.

Capillary action:
Capillary action is another important factor in the upward movement of water in plants. It is the ability of water to rise in narrow tubes against the force of gravity. The xylem vessels and tracheids in plants act as capillary tubes, allowing water to be pulled upward.

Guttation:
Guttation is the process by which water is released from the leaves of plants in liquid form. It occurs when the rate of water uptake by the roots exceeds the rate of transpiration. While guttation can lead to small amounts of water being released from the leaves, it is not responsible for the upward movement of water in the xylem.

Conclusion:
In conclusion, the correct answer is option D, transpiration pull. Transpiration pull, facilitated by cohesion, tension, and capillary action, is the main process responsible for the upward movement of water in plants. Guttation, on the other hand, is a separate process that involves the release of water from the leaves in liquid form.