During the germination of seeds, the seed coat ruptures due to

The correct option is massive imbibition of water.

During the process of seed germination, several sequential physiological changes occur to transition the seed from a dormant state to an active growing seedling. Here is the step-by-step explanation of why water imbibition leads to the rupturing of the seed coat:

1. Imbibition as the First Step:
Dry seeds have extremely low water content and are highly dehydrated. Imbibition is a physical process of adsorption of water by the hydrophilic colloids (such as proteins, cellulose, and starch) present in the seed coat and internal tissues. This occurs along a very steep water potential gradient between the dry seed and its moist surroundings.

2. Generation of Imbibition Pressure:
As these hydrophilic materials absorb water, they swell up enormously. This rapid swelling generates a tremendous amount of physical force known as imbibition pressure. The mathematical representation of water potential driving this movement is:
$${\psi }_w={\psi }_s+{\psi }_p+{\psi }_m$$
where ${\psi }_m$ represents the matric potential (adsorptive forces), which is extremely negative in dry seeds, pulling water inside rapidly.

3. Rupturing of the Seed Coat:
The seed coat (testa) is a tough, protective outer layer. When the internal cells and cotyledons swell due to the massive uptake of water, they exert outward mechanical pressure against the seed coat. Because the seed coat is less elastic, this intense internal pressure eventually causes it to rupture or split open.

4. Subsequent Physiological Activities:
Only after the seed coat ruptures and water enters the cells do metabolic processes like cell division, differentiation of cotyledons, and glycolysis (respiration) accelerate to support growth. Therefore, while these other processes occur during germination, the physical rupturing of the seed coat is directly caused by the initial massive imbibition of water.