Problem 50 - Objective Biology for NEET

Question

Dry seeds when placed in water swells due to (a) Imbibitions (b) Absorption (c) Diffusion (d) Adsorption

Step-by-Step Solution

Answer

The correct answer is (a) Imbibition.

Step 1: Definition of Imbibition

Imbibition is a particular kind of diffusion where water is absorbed by solids, leading to an enormous increase in volume. Seeds and other dry plant organs, when dropped in water, imbibe water and therefore swell.

Step 2: Definition of Absorption

Absorption refers to the process by which one substance is taken into the interior of another substance. In the case of seeds, they do not exactly 'absorb' water, instead, they imbibe water due to the presence of hydrophilic colloids on their surface.

Step 3: Definition of Diffusion

Diffusion is the movement of a substance from its area of high concentration to an area of low concentration. Although diffusion occurs in seeds, it is not the direct cause of the swelling.

Step 4: Definition of Adsorption

Adsorption is a surface phenomenon where molecules of a substance gather on the surface of another substance. Seeds do not swell due to adsorption as the water does not merely remain on the surface but is imbibed within.

Step 5: Conclusion

With all these definitions in mind, when dry seeds are placed in water, they swell primarily because of imbibition. Therefore, the correct answer is (a) Imbibition.

Key Concepts

Imbibition Process

Understanding the imbibition process is crucial when studying how dry seeds interact with water. Imbibition is not just absorption; it's a specialized form of diffusion. During imbibition, water molecules are attracted to the hydrophilic substances within the seeds, such as proteins and carbohydrates. This attraction leads to the water being drawn into the seeds, causing them to swell significantly.

Unlike simple absorption, imbibition does not require the seed to be permeable or to have the water transported across a membrane. Instead, the process relies on the water's capillary action to move through the spaces found in the seed's structure. This is largely because seeds have hydrophilic colloids that create a strong affinity for water molecules.

Hence, when a dry seed encounters water, the imbibition process kicks off, resulting in the seed absorbing water rapidly and swelling almost to the point where it might even split its outer coating. This swelling is a vital step in the germination of seeds, initiating the growth process.

Biological Absorption

Biological absorption is a broader term that describes how living organisms take in substances from their environment and make them part of their own systems. It's a critical process not only in plants but also in animals and humans.

In plants, absorption occurs when nutrients are taken from the soil through roots, or when carbon dioxide is absorbed through leaves. In the context of seeds, it often gets mistaken with imbibition, but there's a key difference. Absorption implies that a substance is moved into and throughout an organism or system.

For seeds, absorption is more related to the later stages of germination, once the seed has imbibed water and begun to activate its internal processes. Nutrients may be absorbed from the surrounding soil as the seed starts to grow. Biological absorption is a complex process that involves both passive means, like diffusion, and active means, which include energy-dependent transport systems.

Diffusion in Biology

Diffusion is one of the fundamental processes that occur in biological systems, allowing for the movement of molecules from a region of higher concentration to an area of lower concentration. It can happen with solids, liquids, and gases and does not require any added energy – it's driven purely by the kinetic energy of molecules in motion.

In the context of seed imbibition, while diffusion is happening as water molecules move into the seed, it's the nature of the imbibition as a special kind of diffusion that explains the rapid intake and swelling. Diffusion elsewhere in biological systems occurs with nutrients moving into cells, oxygen traveling into the bloodstream, and various substances essential to life being distributed within an organism.

It's important to note that diffusion is a slow process and is most effective over short distances, which is why in larger organisms, more complex systems, such as circulatory systems, have evolved to facilitate the movement of essential molecules.