Which micronutrient is needed for plant growth and is essential for enzyme function?

Iron is a crucial micronutrient for plant growth because it plays an integral role in various physiological processes, particularly in the formation of chlorophyll and the functioning of enzymes. It is a key component of several enzymes involved in respiration and photosynthesis, which are essential for a plant's energy production and overall metabolic processes.

Plants require iron in small quantities, but its presence is vital. Deficiency in iron can lead to chlorosis, where leaves turn yellow due to insufficient chlorophyll, impacting the plant's ability to perform photosynthesis efficiently. This highlights the importance of iron not only in growth but also in maintaining the health and productivity of plants through enzyme function.

While calcium, potassium, and magnesium are also important nutrients for plants, they serve different roles. Calcium is primarily involved in cell wall structure and stability, potassium regulates various physiological functions including water regulation, and magnesium is central to chlorophyll production. However, iron's direct tie to enzyme function is what makes it the correct answer in this context.