ESSENTIAL MINERAL ELEMENTS Questions in English

(C) According to Arnon and Stout $(1939)$,the criteria for the essentiality of an element are:
$1$. The plant must be unable to complete its vegetative or reproductive stage of life cycle in the absence of the element.
$2$. The requirement of the element must be specific and not replaceable by another element.
$3$. The element must be directly involved in the metabolism of the plant.
Option $C$ states that the deficiency of one element can be met by another,which contradicts the second criterion of essentiality. Therefore,it is the incorrect statement.

(C) According to the classification of mineral elements in plants,nutrients are divided into two categories based on their quantitative requirements: macronutrients and micronutrients.
Macronutrients are generally present in plant tissues in large amounts (in excess of $10 \ m\,mole \ kg^{-1}$ of dry matter).
The macronutrients include carbon,hydrogen,oxygen,nitrogen,phosphorus,sulphur,potassium,calcium,and magnesium.

(D) Plants require $17$ essential elements for their growth and development.
These are classified into two categories: macronutrients and micronutrients.
Macronutrients are required in large amounts ($> 10 \text{ mmol kg}^{-1}$ of dry matter).
There are $9$ macronutrients: Carbon $(C)$,Hydrogen $(H)$,Oxygen $(O)$,Nitrogen $(N)$,Phosphorus $(P)$,Sulphur $(S)$,Potassium $(K)$,Calcium $(Ca)$,and Magnesium $(Mg)$.
Out of these,Carbon,Hydrogen,and Oxygen are primarily obtained from $CO_2$ and $H_2O$,not from the soil.
The remaining $6$ macronutrients $(N, P, S, K, Ca, Mg)$ are absorbed from the soil in the form of minerals.
Therefore,the correct answer is $6$.

(C) Plants obtain essential mineral nutrients from the soil,but some essential elements are obtained from the atmosphere.
Carbon $(C)$,Hydrogen $(H)$,and Oxygen $(O)$ are the essential elements that are not obtained from the soil.
Carbon $(C)$ is obtained from atmospheric $CO_2$,while Hydrogen $(H)$ and Oxygen $(O)$ are primarily obtained from water $(H_2O)$.
Therefore,out of the essential elements,$3$ elements $(C, H, O)$ are obtained from the atmosphere and water,not from the soil.

(C) According to the classification of essential elements based on quantitative requirements,elements are divided into two categories: macronutrients and micronutrients.
Micronutrients or trace elements are those essential elements that are present in plant tissues in concentrations less than $10 \, m\text{mole} \, kg^{-1}$ of dry matter.
Examples include iron,manganese,copper,molybdenum,zinc,boron,chlorine,and nickel.
Therefore,the correct option is $C$.

(C) Nitrogen $(N)$ is an essential mineral element required by plants in the greatest amount.
It is a major constituent of amino acids,which are the building blocks of proteins.
Nitrogen is also a structural component of hormones (such as auxins and cytokinins),chlorophyll (the primary photosynthetic pigment),and most vitamins (such as $B$-complex vitamins).
Therefore,$N$ is crucial for the overall growth and metabolic activities of plants.

(D) Plants obtain most of their nutrients from the soil,which are mineral in origin.
Carbon,Hydrogen,and Oxygen are primarily derived from the atmosphere $(CO_2)$ and water $(H_2O)$,making them non-mineral in origin.
Nitrogen is absorbed by plants from the soil in the form of mineral ions like nitrate $(NO_3^-)$ and ammonium $(NH_4^+)$,which are mineral in origin.

(B) Critical elements are those macronutrients that frequently become deficient in the soil and limit plant growth.
These elements are $N$ (Nitrogen),$P$ (Phosphorus),and $K$ (Potassium).
Fertilizers that contain these three elements are often referred to as complete fertilizers because they replenish the most commonly depleted nutrients in agricultural fields.