Question

Which of the following element has not been proved to be essential in plants?

• A. Potassium
• B. Sodium
• C. Zinc
• D. Iron

Answer 1

Answer: (B)

Sodium

For an element to be essential, it has to fulfil the following 3 criteria:

1. The element must be essential for normal growth and reproduction and the plant can't proceed its life in the absence of this element.

2. The requirement of the element must be specific and can't be replaced by any other element.

3. The requirement must be direct and shouldn't be the result of any indirect effect.

At present 16 elements are known to be essential for the plants which are grouped into macronutrients and micronutrients.

Macronutrients are required in larger quantities which include Nitrogen, Phosphorous, Sulphur, Calcium, Magnesium, Potassium, Iron, Manganese and Micronutrients are required in lesser quantity which include Molybdenum, Boron, Zinc, Copper, Chlorine.

The macronutrient Potassium is required as a cofactor for many enzymes, the permeability of cell membrane, stomatal movement while the macronutrient Iron is essential for Chlorophyll synthesis, component of cytochromes and ferredoxin.

The micronutrient Zinc stimulates various enzymes like carboxylases and dehydrogenases.

It has been found that presence of Sodium is not considered to be essential for plant growth but it is present in the plants used as food and feed which is important to man and animals.

So, the correct answer is B.