Tag: factors affecting the transport of water and minerals in plants

Water absorption takes place through root. There are two theories to explain the mechanism of water absorption. One is passive absorption and the other is active absorption. Osmotic theory of active water absorption was given by Atkins and Priestley. According to this theory, water is absorbed due to osmotic difference between soil water and tonoplasm. Water moves from soil to root xylem along the increasing gradient of suction pressure.

Xylem vessels are made up of a substance called lignin. In some xylem vessels contains lignocellulose which is the complex structure of lignin and cellulose also present in it. They are long hollow chains of which are made up of tough long dead xylem cells. Each of the vessels is interconnected to each other through a perforation in their common walls. Xylem vessels are hydrophobic in nature i.e, cell wall shows the greater affinity for water. With the help of this particular property only xylem vessel function as transportation of water and solutes from the roots to all parts of a plant. 

 Root pressure is the force in root region that helps to drive water or sap upwards into tracheary elements of xylem. Water is absorbed through the root hairs from the soil. When during low transpiration there is no transpiration pull that time root pressure increases and water moves upwards in xylem elements. Root pressure is actively push up the water to small height in the stem.

So the correct answer is 'Root pressure '.

Lotus have stomata on the upper surface of its leaves. Hence, Coating of Vaseline on its upper surface will hinder transpiration. 

When the concentrations of both the solution (cell sap as well surrounding solution) are same, there is no net movement in the cell. Such solutions are called isotonic solutions. Since it is specified that no change in volume occurs it means that the concentration of the cell sap will be same as that of the concentration of salt.