Question

Which of the following statements is/are true.
(1) The apoplastic movement of water occurs exclusively through the cell wall without crossing any membranes.
(2) Solutes present in a cell (or in any solution) increases the free energy of water or water potential.
(3) The symplastic movement occurs from cell to cell through the plasmodesmata.
(4) Membrane permeability depends on the membrane composition, as well as the chemical nature of the solute.

• A. $1$ and $2$ only
• B. $2$ and $4$ only
• C. $1,3$ and $4$ only
• D. $1,2$ and $4$ only

Answer 1

Answer: (C)

The absorbed water from the root hair moves towards the xylem which helps in the ascent of sap. According to Munch, 1930, there are mainly two paths:
1. The apoplast is a type of or path of movement of water molecules absorbed by the root hairs. In this way, water passes from the root hairs to xylem through the non-living path or through the walls of the intervening cells without crossing any membrane or cytoplasm.
2. In symplast path, the water molecule moves from one cell to the other through their protoplasm and by crossing their plasmodesmata. This path is called transmembrane pathway.
So the statements 1 and 3 are correct.
Membrane permeability is the ability of any membrane to allow any passage of gases, water or any other molecules, solutes or other liquids through it.
Based on the permeability, there are following types of membranes:
1. Impermeable membranes do not allow any passage of any molecules through them, like a suberised cell wall.
2. Permeable membranes allow every molecule to move through them, like the cell wall of plants.
3. Semi-permeable membranes allow passage of solvents through it but do not allow the solutes to pass through. An example of this type is animal bladder, egg membrane.
4. Selectively permeable membranes are a special type of semi-permeable membrane which also allow certain solutes to pass, like tonopast and plasma membrane.
Membrane permeability is dependent on chemical nature of the membrane and of the solute.
When some solute is added to a solvent, solute potential (osmotic potential) or $\psi$ s decreases.