Question

Water movement from soil into plant roots and subsequently into upper portion of the plant is partly due to phenomenon of

• A. Edema
• B. Osmosis
• C. Reverse Osmosis
• D. Evaporation

Hint:

Remember that the initial absorption of water by root hairs is driven by osmosis, while the high-altitude ascent in tall trees is supplemented by transpiration pull.

Answer 1

The Correct Option is B

Concept:
Osmosis is the spontaneous net movement of solvent molecules through a selectively permeable membrane from a region of lower solute concentration (higher solvent potential) to a region of higher solute concentration (lower solvent potential).
In biological systems, osmosis plays a fundamental role in maintaining cellular turgidity and driving fluid transport across cellular boundaries.

Step 1: Identifying the Concentration Gradient:
The soil surrounding the plant roots contains moisture with a very low concentration of dissolved inorganic minerals, functioning as a dilute solution.
In contrast, the fluid inside the root hair cells (cell sap within the central vacuole) contains a relatively higher concentration of dissolved sugars, organic acids, and inorganic salts.
This establishes a steep water potential gradient between the soil water and the internal cellular fluid of the root hairs.

Step 2: Mechanism of Water Influx Across the Root Membrane:
The plasma membrane of root epidermal cells acts as a natural semi-permeable membrane.
Because of the difference in osmotic potential, water molecules move spontaneously from the soil solution into the root epidermal cells via endosmosis.
This continuous influx builds up positive hydrostatic pressure within the root cells, commonly designated as root pressure, which assists in pushing the absorbed water upward through the xylem conduits.

Step 3: Analysis of Incorrect Options:
Edema represents an abnormal accumulation of fluid within animal body tissues resulting in localized swelling, which is completely irrelevant to plant physiology.
Reverse osmosis is an artificial non-spontaneous process where an external pressure exceeding the osmotic pressure is applied to force solvent from high to low concentration.
Evaporation contributes to the transpiration pull at the leaf surfaces, but the primary phenomenon driving water entry and cellular movement in the roots is osmosis.
Final Answer:
Hence, the movement of water from soil into plant roots is partly due to osmosis, which corresponds to option (B).