Which of the following are plant macronutrients?

• A. Molybdenum, chlorine, and fluoride
• B. Iron, zinc and manganese
• C. Boron, copper, and cobalt
• D. Magnesium, sulfur, and calcium

Answer: (D)

Plants need some minerals in larger amounts to build tissues and drive growth; these are called macronutrients. Magnesium, sulfur, and calcium fit this category because each is required in substantial quantities and plays essential roles: calcium helps build and stabilize cell walls and membranes, magnesium sits at the center of the chlorophyll molecule and acts as a key enzyme cofactor, and sulfur is a component of important amino acids and proteins. The other groups listed are micronutrients, needed much less in the plant’s diet, such as iron, zinc, and manganese, which are important for enzyme activity but required in far smaller amounts; chlorine is also a micronutrient; cobalt is not generally considered essential for most plants, and fluoride isn’t a recognized plant nutrient. Therefore, the trio that represents macronutrients is magnesium, sulfur, and calcium.