Question

Movement of a nutrient ion in response to concentration gradient is _______

• A. Massflow
• B. Diffusion
• C. Osmosis
• D. Root interception

Hint:

To distinguish between the two primary nutrient transport pathways: 1. Concentration Gradient $\to$ Diffusion (important for Phosphorus and Potassium). 2. Water Flow Transpiration Pull $\to$ Mass Flow (important for Nitrogen and Calcium).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Nutrients in soil reach the root surface through three primary physical mechanisms: mass flow, diffusion, and root interception.

Step 2: Detailed Explanation:
Let us evaluate each transport mechanism:
Diffusion (B): This is the movement of individual ions or molecules from a region of higher concentration to a region of lower concentration in response to a concentration gradient.
When plants absorb nutrients from the root surface, they create a nutrient-depleted zone around the root, establishing a concentration gradient.
This gradient drives the diffusion of nearby ions toward the root surface.
This is the primary pathway for immobile nutrients like phosphorus ($\text{H}_2\text{PO}_4^-$) and potassium ($\text{K}^+$).
Mass Flow (A): This is the bulk movement of nutrients along with flowing soil water driven by transpirational pull or hydraulic gradients.
It is the primary pathway for mobile nutrients like nitrate ($\text{NO}_3^-$) and sulfate ($\text{SO}_4^{2-}$).
Osmosis (C): This is the movement of water molecules across a semi-permeable membrane from a region of low solute concentration to high solute concentration.
Root Interception (D): This is the physical contact made between roots and soil nutrients as roots grow through the soil matrix.

Step 3: Final Answer:
The movement of ions in response to a concentration gradient is called Diffusion, which corresponds to option (B).