During the rainy season, wooden doors often swell and become difficult to open or close; which plant physiological process is mainly responsible for this swelling of wood?

Introduction:
Many everyday phenomena can be explained with basic concepts from plant physiology and physical chemistry. A familiar example is the way wooden doors become tight and difficult to move during the rainy season. The wood absorbs moisture and swells, causing expansion. This question asks you to identify the specific process that describes the absorption of water by dry colloidal substances like wood and seeds.

Given Data / Assumptions:
- The observed phenomenon is swelling of wooden doors in rainy season. - The options are imbibition, plasmolysis, diffusion and osmosis. - We assume that the wood is hygroscopic and can absorb water vapour from humid air. - The task is to match this swelling with the correct physiological or physical process.

Concept / Approach:
Imbibition is defined as the absorption of water by solid colloidal particles such as dry seeds, wood and cell walls, leading to swelling. It is a special kind of diffusion in which water molecules move into the spaces of a porous substance due to attractive forces. The other terms have different meanings: plasmolysis is the shrinking of cell contents in a hypertonic solution, diffusion is the general movement of molecules from higher to lower concentration, and osmosis is the movement of solvent through a semipermeable membrane. The swelling of wooden doors due to water uptake fits the definition of imbibition best.

Step-by-Step Solution:
Step 1: Recognise that wood acts like a dry colloidal system capable of absorbing water. Step 2: Recall that imbibition describes water absorption by such colloids, causing volumetric expansion. Step 3: Understand that plasmolysis applies only to living cells placed in hypertonic solution, which is not the case for dead wood. Step 4: Note that simple diffusion lacks the idea of swelling of a solid matrix, while osmosis requires a semipermeable membrane. Step 5: Conclude that imbibition is the correct process explaining swollen doors in rainy weather.

Verification / Alternative check:
Plant physiology books give classic examples of imbibition, such as swelling of wooden doors in the rainy season and swelling of dry seeds when soaked in water. Swelling exerts imbibition pressure, which can be very high. These sources explicitly label the wooden door example as imbibition, not as plasmolysis or osmosis, which reinforces the correctness of this answer for exam purposes.

Why Other Options Are Wrong:
Plasmolysis: Occurs in living plant cells when they lose water in a hypertonic solution, causing the plasma membrane to shrink away from the cell wall; wood is dead tissue and does not plasmolyse. Diffusion: A general process of molecule movement; while imbibition involves diffusion of water, diffusion alone does not describe swelling of colloidal solids. Osmosis: Involves movement of solvent across a semipermeable membrane; the wooden door has no living membrane that separates two solutions, so osmosis does not strictly apply.

Common Pitfalls:
Because osmosis is widely taught as the movement of water, students often apply it too broadly whenever water is involved, leading them to choose osmosis instead of imbibition. Another confusion is between diffusion and imbibition, since both involve movement of molecules. The key difference is that imbibition involves absorption by solid colloids and causes swelling, while diffusion can occur entirely in liquid or gas without any swelling solid. Remembering the classic examples listed under imbibition will help prevent these errors.

Final Answer:
Swelling of wooden doors during the rainy season is mainly due to Imbibition.