Micronutrients are important for plants because they:

Micronutrients are essential for plants primarily because they play crucial roles in various physiological processes, even though they are required in smaller quantities than macronutrients. These micronutrients include elements such as iron, manganese, zinc, copper, molybdenum, boron, and chlorine, and each one is vital for specific functions within the plant, such as enzyme activation, synthesis of chlorophyll, and the overall metabolism that supports growth and development.

For instance, iron is essential for the formation of chlorophyll and thus plays a significant role in photosynthesis, while zinc is important for enzyme function and plant hormone production. Without adequate micronutrients, plants can exhibit signs of deficiency that may lead to stunted growth, poor yields, and reduced resistance to disease.

In contrast, the other options are misleading regarding the role and significance of micronutrients. They are not needed in large quantities, nor are they only required during flowering; in fact, they are necessary throughout all stages of a plant's life cycle. Additionally, micronutrients have a substantial impact on plant growth and health, countering the notion that they have no influence. Thus, the correct choice highlights the significance of micronutrients in the physiological processes that are crucial for effective plant development.