Question

I was studying transportation in plants and I came across two ways in which plants transport water.

The first one is root pressure. In this method, epiblema cells of root hairs actively absorb minerals from the soil. This creates a concentration gradient of water inside the roots and outside the roots and hence leading to a formation of a column of water. But this method can only be used to transport water for short heights.

In tall trees, the method of transpiration is seen. The evaporation of water molecules from the aerial parts of a plant leads to a phenomenon like a suction pull therefore transporting water.

But in the night, the stomata are closed which means that transpiration can't take place. And root pressure also cannot satisfy the needs of the tree because it is a tall tree.

Then how tall trees transport water in night?

Answer 1

Tall trees transport water at night utilizing the cohesion-tension theory. Cohesion and adhesion of water molecules help maintain water movement in the absence of transpiration.

Step-by-step explanation:

The way tall trees transport water at night is through the cohesion-tension theory of sap ascent. Even though transpiration is reduced at night due to closed stomata, the cohesion and adhesion properties of water molecules allow for the maintenance of a 'continuous water column' within the xylem tissues of plants. This tension helps to keep water moving up from the roots to the leaves, albeit at a slower rate than during the day when transpiration is active.

Transpiration is the main driver of water movement in plants. It is caused by the evaporation of water at the leaf surface, creating negative pressure (tension) that pulls water up from the roots. At night, when stomata are closed and transpiration stops, the water is held in the stem and leaf by adhesion and cohesion between water molecules. This is known as the cohesion-tension theory of sap ascent.