Question

Which one group is of micro-elements?
(a) Mn, Cu, Ca
(b) Na, K, B
(c) Na, Ni,Cl
(d) Cu, Mo, Zn, Mn, Fe

Answer 1

Along with sunlight, water, and air, a plant also needs some nutrients for its growth and reproduction. These are termed as ‘essential elements’. There are 17 essential elements which can be classified based on their quantitative requirements in a plant.

Complete step by step answer:
The botanists have grouped the essential elements into macronutrients and micronutrients. Macronutrients are required in large quantities i.e. more than $10 mmol/kg$ of dry matter. These include carbon, oxygen, hydrogen, nitrogen, potassium, phosphorus, sulfur, calcium, and magnesium.
Micronutrients or trace elements are required in very small amounts i.e lower than $10 mmol/kg$ of dry matter. These are iron, manganese, copper, molybdenum, zinc, boron, chlorine, and nickel.
- There are four elements that have been found to have participated in the metabolic activities of certain plants. These are known as non-essential elements or beneficial elements. They include sodium(Na), silicon (Si), Cobalt(Co) and selenium (Se).
- Copper is a component or activator of enzymes involved in photosynthesis like RuBP carboxylase or in enzymes of electron transport chains like cytochrome oxidase.
- Zinc is involved in the synthesis of auxins like IAA or proteins and RNA. It is involved in the evolution and utilization of carbon dioxide.
- Molybdenum is involved in nitrogen metabolisms like nitrogen fixation and nitrate reduction as it is a cofactor of enzymes like nitrogenase.
- Manganese plays its role in the metabolic reactions and photolytic evolution of oxygen and activates enzymes of the oxygen-evolving complex.
- Iron helps in the redox reactions in electron transport. It also helps in the development of chloroplasts and chlorophyll.
So, the correct answer is ‘(d) Cu, Mo, Zn, Mn, Fe.’

Note:
- In 1939, Arnon and Stout proposed the criteria of essentiality of elements. Any element which does not meet these criteria is not considered essential.
-essential elements are classified into mineral and non- mineral elements. Those that can be derived primarily from carbon dioxide and water are considered non-essential elements.E.g Carbon, Hydrogen, and Oxygen. The mineral elements are absorbed from the soil primarily in the form of inorganic ions.