Transport of water

The roots, with the help of root hairs, absorb water and together with it, minerals from the soil. Hairs are produced in large numbers by each root, as outgrowths of the epiblema. These are unicellular structures; resembling fine tubes, and lay in close contact with the water surrounding soil particles. The plasma membrane of the root hair is semi permeable and lets in the water molecules from the soil by the process of osmosis. In osmosis, water moves from an area where its molecules are present in a higher concentration to one where they are less concentrated, when the two are separated by a semi permeable membrane. As the concentration of water molecules in the soil is higher than that in the root hairs, water passes from the soil into the root hairs. The water when passes father and father into the root tissues by cell –to cell osmosis, until it reaches the xylem of the root. It moves up the xylem vessels and reaches the leaves due to a pull created by transpiration, which has been discussed next.

Transpiration helps absorption

You might recall that transpiration is the process by which plants get of excess water in the form of water vapor.

Plants absorb more water than is required because if they did not do so, they would not get enough minerals. The excess water leaves the plant trough the stomata of the leaves. As transpiration takes place rapidly during the daytime, the leaves start running short of water, or develop a water deficit condition.

This condition creates a force of suction, which pulls up water from the xylem of the root, up the xylem of the stem and into the leaves. Due to transpiration, the roots are left with less water the surrounding soil and this, in turn aids process of absorption. The upward movement of water and minerals is called ascent of sap.

Absorption on minerals

This is not the only way by which plants absorb minerals from the soil. They also absorb them by diffusion. Diffusion is a process in which the solute moves from an area of higher concentration to an area of lower concentration. Naturally, plants can absorb minerals by diffusion when their concentration is higher in the soil than inside the root.

There is yet another process by which plants absorb minerals. This is called active absorption. In this process, minerals enter the root even if their concentration is higher inside the root than in the soil. Te process is called `active’ absorption because unlike diffusion, it requires the plant to expended energy.

Transport food

Te food prepared in the leaves is transported to other parts the plant in the form of glucose. Glucose is carried from the leaves through the phloem, or more specifically, the sieve tubes of the phloem. The movement of food from the leaves to the other parts of the plant where it is utilized or stored is called translocation of food. While the xylem transports water and minerals upwards, the phloem transports food upwards as well as downwards.