Active absorption: Active absorption is the absorption of ions with the help of

metabolic energy produced in the cells.

Translocation in plants: Translocation in plants represents the movement or flow of

water and mineral salts and of the food produced in the leaves.

We know that water and mineral salts are taken up the stem in plants through the vessels of xylem tissue. Scientists think that the force produced by transpiration, capillary action and root pressure cause the cell sap to reach the leaves of plants. In this way water reaches leaves, food is produced there. Then phloem tissue takes active part in the translocation of food produced by photosynthesis to the different regions of a plant. The food is translocated through the sieve tubes of phloem tissue. Different organic compounds in plants move through phloem tissue at the same time in opposite directions. The compounds in the lower region flow downwards and compound synthesized in the upper region flow upwards and the substances synthesized in the middle region flow both the directions upwards and downwards.

Necessity of translocation in plants

Translocation refers to the movement of any substance from one part of the plant to another. Movement or transportation of water and mineral salts in plants called

translocation in plants. All the scientists agree with the necessity of translocation of water and mineral substances in plants. Now, the matter of consideration is that the water and mineral substances, that are to be used, must be taken up to the place where the reactions will occur. This is why the translocation of water and mineral salts is very important. Water and mineral salts being absorbed through the root hair reach the vessels of the xylem tissue crossing the cortex region and gradually reach the leaves along with the current or flow of transpiration. Food is produced there in the leaves. The food produced in the leaf reaches the different regions of a plant through sieve tubes of phloem tissue. If the flow in the xylem vessels or phloem sieve tubes is blocked for any reason, the plant would have to die. This is why it can be said that translocation in plants is a very important activity for the existence of their life.

Translocation of water and minerals: We have already acquired some ideas about

osmosis and transpiration. Plants absorb water from the soil with the process osmosis. It is accomplished mainly with the aid of root hairs. Side by side plants also absorb mineral nutrients from the soil though the process of absorbing water and the process of absorbing mineral salts are much different. You will be able to know much more detailed about it at your higher level of education. Water and mineral salts dissolved in it are collectively known as cell sap. Now, we will know how the cell sap from the root reaches the top most branches and leaves of a plant.

Ascent of sap: Roots absorbs water and mineral salts. The cell sap ascends slowly

upwards with the influence of different factors. Concurrently, the lateral translocation of cell sap also occurs. Translocation of cell sap is categorized into two steps: 1) the arrival of soil water and mineral salts from root hair to the vascular tissue of the root and 2) translocation from vascular bundle of root to leaves. At the first stage, osmosis, diffusion and suction from transpiration etc. play their important role in the absorption and translocation of water and mineral salts. The water and the mineral substances absorbed by root hair move to the adjacent cell by the process of osmosis. From that cell they move again to the next cell. Moving in this way, water and mineral substances that once reach the vascular bundle of the root, ultimately, reach the

mesophyll tissue of leaves through the vascular bundle of the stem.

Work: Experiment on the demonstration of the ascent of

sap in a plant.

Essentials: Peporomia plant, bottle of glass, water and

safranin.

Procedure: Taking some water in a bottle of glass add some drops of safranin to it.

into water. Now place the bottle somewhere with the plant for some hours and note down the result from a careful observation.

Translocation of the substances produced in photosynthesis: You have learnt earlier

that plants absorb water by the process osmosis. The water is conducted to the leaves at the top most regions of a very long plant. These very leaves utilize water for the process photosynthesis. Chloroplasts produce the food starch in presence of light by mixing water with the CO2 taken from the air. The food produced in that way is conducted to the different parts of a plant. Every cell of a plant derives its energy to perform its metabolic activities by using the food through the process respiration. After the completion of deriving energy through respiration, the remaining food is stored in some special regions of a plant. In potatoes (stem), sweet potatoes (root), aloes (leaf) and in different fruits and seeds, the food is usually stored. Now, we will study how the food produced in photosynthesis is conducted to the different regions of a plant body.

Phloem translocation: As the leaves and the roots grow away from each other, there

must be a rapid and effective transport system in between them for the conduction of food. This is done by sieve tubes of phloem. Phloem is one of the important bundles of vascular bundle. We knwo that there are xylem bundles and phloem bundles in a vascular bundle. In phloem bundle, there are sieve tubes, companion cells, phloem parenchyma and bast fibers. Sieve tube is a kind of thin walled living cell without nucleus. Being longitudinally side by side, they form a net like structure. The septa in between them being disappeared in some places develop sieve shaped forms. This is why food substances can easily move from cell to cell. In winter, these openings are blocked because of the deposition of chemical substance callose, and thus the movement of food is inhibited. At the advent of summer, the callose is removed being degraded and the movement of food increases.

Transpiration: Life cannot be imagined without water. Plants mainly absorb water they

require at their roots. They use a very little part of the absorbed water for their metabolic activities. The remaining part of the water is lost outside the plant body. The physiological process by which generally the land plants through their aerial part lose water in the form of water vapour is called transpiration. On the basis of aerial parts through which this process occurs, transpiration is categorized into three: stomatal transpiration, cuticular transpiration and lenticular transpiration.

1) Stomatal transpiration: There are special types of openings with two guard cells in