Question

Which of the following elements are macronutrients?
Co, Ba, Mg, S, I, Mn
(a) I and Mn
(b) Mg and S
(c) Co, Mg and Mn
(d) Co and Mn

Answer 1

Hint: Plants require various elements for their proper growth and development. Certain elements are essential for their growth and metabolism. They help in making cell membrane permeable to certain substances, osmotic concentration gradient, involved in enzymatic action, act as coenzymes etc.

Complete answer:
The essential elements that are required by plants are divided into two types on the basis of their quantitative needs. Some elements are required in large amounts while others are required in lesser amounts.
The elements that are required in very large amounts are called macronutrients. They are generally present as more than 10mmole per Kg of dry matter. Macronutrients are nine in number. These are oxygen, hydrogen, nitrogen, carbon, magnesium, calcium, potassium, phosphorus and sulphur.
The magnesium helps in the activation of enzymes that helps in respiration and photosynthesis. It also plays an important role in the synthesis of DNA and RNA. Magnesium is present in the chlorophyll.
Sulphur is present in the various coenzymes. Several vitamins such as thiamine, biotin etc. contain sulphur as an important constituent. Methionine and cysteine (amino acids) also contain sulphur.
The elements that are required in very less amounts are called micronutrients. They are generally present as less than 10mmole per Kg of dry matter. They are eight in number. Iron and manganese are examples of micronutrients.
Some essential elements do not fall in either category. Examples include cobalt and selenium. These elements are used by higher plants.

Thus the answer to the above question is option (B) Mg and S because they are required in very large quantities. They are involved in various metabolic and structural processes of the plant.

Note: On the basis of functions, the essential elements are divided into four types. Some elements help in activation or inhibition of enzymes e.g. Mg2+. Some elements maintain osmotic potential e.g. potassium. Some elements form the structure of plant cells e.g. carbon. Magnesium is an element that acts as an energy-related component in plants.