Question

Plants do not use all water they absorb. Most of it is lost by transpiration. Why then plants absorb more water than they need?

Answer 1

absorpation of water is known as ascent of sap.
actually a plant also needs some kind of minerals and it obtain these minerals from the underground when these minerals are mixed with water and the solution of mineral and water is called sap.
It is a necessary evil


Hope u got that

Answer 2

Plants absorb water in large quantity because in photosynthesis carbon dioxide and water are used as raw material for the synthesis of glucose. Water is absorbed by root while carbon dioxide is taken from the atmosphere through stomata. So for photosynthesis stomata should be open. If stomata remains open transpiration takes place continuously i.e. plants synthesize food on the cost of loss of water.

C4 plants are are twice more efficient as C3 plants because they lose only half amount of water as C3 plants are the synthesis of same amount of glucose or fixation of carbon dioxide.