What is the first step in seed germination?

The first step in seed germination is water absorption, also known as imbibition. When a seed is planted in a suitable environment, it begins to take up water from the soil. This process is crucial because it activates the metabolic processes within the seed, leading to the breakdown of stored nutrients, which are necessary for the growth of the embryo. Water also helps to soften the seed coat, making it easier for the embryo to emerge.

Once initial water absorption occurs, the seed swells and may crack open, allowing for the next stages of germination to take place. The biochemical reactions that are triggered by the presence of water are vital for energy mobilization and growth, ultimately leading to the sprouting of the seed.

The other options, while important to seed germination and plant growth, occur either after the initial water uptake or are supportive aspects rather than the foundational first step. Seed coat hardening does not typically occur in this context as seeds often have varying degrees of permeability to water. Light exposure and soil temperature regulation are also essential for the successful growth of seedlings but are not prerequisites for the germination process itself. Therefore, water absorption is clearly identified as the critical initial step in seed germination.