Q.How are the minerals absorbed by the plants?

Step 1. Why active transport is usually needed. Most soil minerals exist as charged ions, which cannot freely cross the lipid cell membrane, so the bulk of mineral uptake by roots requires energy-consuming active transport; mineral absorption is independent of water absorption.

Step 2. Passive absorption. Ions can move into root cells purely by diffusion, from a region of higher concentration to lower concentration, without any energy expenditure -- by direct ion exchange, indirect ion exchange, or mass flow.

Step 3. Donnan equilibrium. A special case of passive absorption: certain anions become fixed on the inner face of the cell membrane once inside the cell and cannot diffuse back out, so additional mobile cations are drawn in, even against their own concentration gradient, to electrically balance these trapped anions.

Step 4. Active absorption. Ions are also taken up against their concentration gradient, which requires energy from respiration, supplied through ATP; roots deprived of oxygen show a sharp drop in active mineral uptake. …

Distinguish passive vs active absorption, explain Donnan equilibrium, and describe the …

• Describing only active absorption and omitting passive absorption (or vice versa), when the question expects both routes …