Question

Mention the criteria for essentiality of an element. Give one example of an essential element.

Answer 1

Hint: Essential elements are those minerals of the Earth which are vital for the growth of plants. Examples of such elements include phosphorus which is part of nucleic acids, potassium which is used for the anion- cation balance in cells, etc.

Complete Step by Step Answer:
The criteria for the essentiality of an element is given in three points:
- The function of that element should be absolutely vital for the growth and development of the plant. In the absence of that element, the plant should not be able to complete their life cycle or set its seeds.
- The demand for that particular element should be specific and not replaceable by any other element. In simple words, the deficiency of that element cannot be fulfilled by supplying another element.
- The function of the element should be directly involved in the metabolism of the plant.

Additional information: There are a total of 17 essential elements which meet the requirements mentioned above. They are divided into two categories known as micronutrients and macronutrients on the basis of their requirements by the plant.
An example of an essential element is nitrogen. This element is required by the plants in the most amount. It is absorbed as nitrate ion ${ { NO }_{ 3 } }^{ - }$ but in some cases, it is also absorbed as nitrite ion ${ { NO }_{ 2 } }^{ - }$ or ammonium ion ${ { NH }_{ 4 } }^{ + }$. Nitrogen is an element that is required by all parts of the plant from meristematic tissues to metabolically active cells. This is because it is the main component of proteins, nucleic acids, vitamins, and hormones.

Note: Macronutrients are nutrients that are required in large amounts such as 10mmole ${ Kg }^{ - 1 }$ or more. It consists of 9 nutrients which are carbon, hydrogen, nitrogen, oxygen, potassium, sulfur, phosphorus, calcium, and magnesium.
Micronutrients are needed in quantities less than 10mmole ${ Kg }^{ - 1 }$. It consists of 8 elements which include iron, nickel, manganese, copper, molybdenum, boron, zinc, and chlorine.