Question

How does transpiration help photosynthesis?

Answer 1

Hint: Land plants absorb large quantities of water from the soil. The leaves use 1% water for photosynthesis and plant growth. Most of the water is lost through the leaves in the form of water vapour.
The loss of water in vapour form from the exposed parts of a plant is called transpiration. The extent of water loss due to transpiration is quite high.

Complete answer:
Transpiration is a physiological process which occurs in plants. It is controlled by various features or climatic conditions like position and opening of stomata, thickness and number of cuticles, etc. It is influenced by light, because the stomata is open in light, or by pH, $CO_2$ and hormones.
Transpiration is helpful in various ways for plants –
It helps in the water absorption from the soil.
It supplies the water to the plants for the process of photosynthesis which is very useful in making the food.
It also helps the movement of water from the roots with the help of xylem to other parts of the plants.
The evaporation of excess water helps the plants to provide cooling temperature of leaves and protect them from the rays of sunlight or heat.
It exerts a tension on water through xylem which are responsible for the ascent of sap.

Note:
Transpiration is important but in excess it is harmful too in various ways –
It leads to the growth of plants.
It also causes lack of water or moisture of plants which is necessary for their development or we can say it causes injury to the plants by desiccation.
Stomata is responsible for gaseous exchange but loss of water from stomata is also a problem because due to rays of sunlight the water is lost in high amounts and it causes problems.