Transpiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere. Transpiration is essentially evaporation of water from plant leaves.The survival of plants is dependent on a number of factors which include water, minerals, gases, and nutrients they receive. The movement of gas, water, and nutrients in plants are carried out in components. They take in carbon dioxide from the air through the stomata present in their leaves and they absorb compounds of nitrogen, phosphorus, etc., from the soil by their roots. If the distance to be traversed is relatively small, diffusion process occurs. As the distances increases in tall trees, a well-developed transportation system arises as these movements of substances have to be facilitated with extreme care.
The amount of energy required by plants is lower compared to that of animals, hence there is a requirement of slower transportation. In plants, a tube-like passage made up of vascular tissues called xylem and phloem are two modes of transportation. Water and minerals travel upwards through the xylem, while phloem transport synthesized food to other parts of the plant. The movement of water and other nutrients from one part of a plant to another is called translocation. Water gets absorbed by osmosis while minerals by active transport. The method used in the upward movement of water through the xylem is determined by the cohesion-tension theory. Here the driving force of transport is transpiration. In this process, cohesion is responsible for driving more water through the xylem and excess water molecules are pulled up by the pulling force which later evaporates through the tiny pores of stomata.
Like water, minerals are also necessary for plants to survive. About 16 minerals are necessary for plants. These minerals are present in soil in the form of inorganic salts such as nitrates and phosphates. In soil, these minerals get dissolved in water and are absorbed by roots along with water. From roots, the minerals are transported to various parts of a plant along with water by xylem vessels by same procedure as described earlier.
Thus, in plants both water and minerals are transported from roots to upper parts (stems, leaves, flowers and fruits) by xylem vessels.
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