The combined forces of root pressure, capillary action, and transpiration are the processes that aid in the upward movement of water molecules throughout the entire plant.

The pressure-flow hypothesis explains how the sugar molecules from a source cell forms a high concentration inside the cells of the phloem. This causes an osmosis that draws the water from the xylem to go into the cells of the phloem. As a result, there is a presence of pressure that forces the nutrients to go into a region called the sink cell.

Capillary action is not sufficient to lift the water at a certain height due to the stronger force of gravity. In order for the water to move upward, the combined forces of root pressure, capillary action, and transpiration are all needed.

The rate of photosynthesis will decrease because the rate of flow of nutrients and water decrease when transpiration decreases, whenever the stomata close. . Also when the stomata close there is less carbon dioxide for photosynthesis.