Mineral Nutrition — Practice

Question 1

Differentiate between macronutrients and micronutrients with examples.

Accepted Answer

Macronutrients are needed in large amounts (more than 10 mmole/kg dry matter): N, P, K, Ca, Mg, S. Micronutrients are needed only in trace amounts (less than 10 mmole/kg): Fe, Mn, Zn, Cu, Mo, B, Cl.

Question 2

What is the role of leghaemoglobin in nitrogen fixation?

Accepted Answer

Leghaemoglobin is a pink, oxygen-scavenging protein in root nodules. It binds free oxygen, keeping the nodule environment nearly anaerobic and protecting the oxygen-sensitive nitrogenase enzyme.

Question 3

Name three free-living nitrogen-fixing organisms.

Accepted Answer

Azotobacter (aerobic), Clostridium (anaerobic), and the cyanobacteria Nostoc or Anabaena.

Question 4

How does Rhizobium form a symbiotic relationship with legumes?

Accepted Answer

Rhizobium enters through curled root hairs, forming an infection thread that grows into the root cortex. The bacteria are released into cortical cells and differentiate into bacteroids, while the cells divide to form a visible nodule. The bacteroids fix N2 into ammonia using nitrogenase, the plant supplies them with carbohydrates, and leghaemoglobin protects the nitrogenase from oxygen.

Question 5

What is the critical concentration of an element?

Accepted Answer

It is the concentration below which a plant shows deficiency symptoms. The range between deficiency and toxicity is narrow, especially for micronutrients.

Practice — Mineral Nutrition

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