Question

Active absorption is affected by
A. Osmotic concentration
B. Associate tissue structure
C. Transpiration
D. Sucking capacity of root hair

Answer 1

Hint: The absorption of solute occurs against a concentration gradient that is from a region of lower concentration of solute to the region of higher concentration of solute. This is active absorption.

Complete answer:
During active absorption the roots of a plant absorb water with the help of root pressure that is developed due to low concentration of water molecules in the roots. Active absorption occurs in the plants that are well water and transpiration in them is very low, quoted Jenner. Active transpiration is carried out according to two theories:
Active absorption by osmosis – Atkins and Priestely discovered this theory. According to this theory the cells in the root behave as ideal osmotic systems through which the water from the soil moves up the plant through the xylem of roots. When the concentration of water is low in the root cells then the water will enter them as per the osmotic principle by endosmosis. This continues till the water concentration in the soil and root cells become the same. No energy is required in this process of active transport.
Active absorption without osmosis – Thimann and Kramer gave this theory. They said that with the expenditure of metabolic energy the active absorption against a concentration gradient is also possible. But the evidence proving this theory is rare.

Hence, the correct answer is option (A).

Additional information:
-Apart from active absorption passive absorption is also seen. In passive absorption no metabolic energy is required and it is just basic absorption where roots act as organs of absorption. This occurs during daytime when transpiration is high that increases the transpiration pull of water from the roots. Passive transpiration is similar to diffusion.
-Water absorbed in the active transport moves through the protoplast of the plant cells. Whereas in the passive absorption it moves through the apoplast (non-living part) of the plant cells.
-Active transport occurs only when the level of water in the soil is high.

Note: The absorption of water in active transport is by the roots and it will cease in the absence of roots. It is a slow process which is easily inhibited by metabolic inhibitors or toxins.