Question

If the root hair cell is surrounded by a dilute solution of mineral ion. The mineral ions will move

A. Against the concentration gradient by diffusion or osmosis.
B. Against the concentration gradient by active transport.
C. Along the concentration gradient by diffusion or osmosis.
D. Along the concentration gradient by active transport.

Answer 1

Hint: The concentration of mineral ions in soil is less than that in roots . Plants uptake mineral ions through roots and root hairs. Then the mineral ions are transported to other plant parts via vascular bundles like xylem.

Complete answer: -Soil acts as a reservoir of nutrients and essential elements that contribute to the growth and development of the plants. Soil also harbors nitrogen-fixing bacteria, other essential microbes and holds water.
-Passive transport is the one in which energy is not required for the movement of particles whereas active transport is the transport that consumes energy for the movement of substances from one point to another.
-Diffusion is a type of passive transport in which energy is not utilized. Diffusion of water molecules is referred to as osmosis. The net result in diffusion is substances moving from regions of higher concentration to the region of lower concentration.
-Diffusion rates are affected by the gradient of concentration, temperature, pressure, and the permeability of the membrane which is separating the two media. Gaseous movement within the plant body can occur only through diffusion.
-Simple diffusion does not depend on the living system and does not require carrier protein but in facilitated diffusion, the movement of substances is carried out by carrier proteins usually present on the membrane separating the two media.
-In active transport energy is required to pump molecules against the concentration gradient which is carried out by specific membrane proteins. Active transport moves molecules from regions of lower concentrations to regions of lower concentrations.
-Movement in diffusion or passive transport is downhill whereas movement of substances in active transport is uphill. In diffusion, substances move in a random fashion unless facilitated by membrane proteins.
-Both facilitated diffusion and active transport require membrane proteins therefore both of them are highly selective and are liable to saturate. They are also under hormonal regulation.
-Usually, water is passively absorbed by the roots and the root hairs, but mineral ions are not passively absorbed by them because minerals are present in the soil as charged particles or ions which cannot move across cell membranes.
-The concentration of minerals in the soil is usually lower than the concentration of minerals in the roots. This accounts for another reason that the mineral ions will move against the concentration gradient by active transport.
Hence, the correct answer is option (B).

Note: When a cell is isolated from plants and put in a hypertonic solution, then the cell loses water and becomes plasmolyzed. However when a cell is placed in a hypotonic solution then it gains water and becomes turgid.