(a) Hydroponics, Julius Von Sachs (1860)

(b) (i) Solanum lycopersicum (tomato)

(ii) Hibiscus asculentus (ladiesfinger)

(iii) Solanum melongena (brinjal)

(c) Aerating tube Provides oxygen for the normal growth and development of the roots growing in the liquid solution. Feeding funnel is used to add water and nutrients in the hydroponic system when required.

Nitrogenase is the most crucial enzyme found in the root nodules for $\mathrm{N}_2$-fixation. It is a Mo- Fe protein that catalyses the conversion of atomospheric nitrogen to ammonia. Pink coloured pigment called leghaemoglobin creates anaerobic conditions for the functioning of nitrogenase enzyme.

Critical Concentration	Deficient
A concentration of a nutrient measured in tissue, just below the level that gives maximum growth is defined as critical concentration. e.g., N, P and K are known as critical elements.	The concentration that is below the critical concentration and the deficiency of nutrient element can lead to a gradual fall in the plant growth is called deficient.

	Critical concentration	Deficient
Zn	0.5-1%	less than 0.5%
Fe	3.5-5%	less than 3.5%

Carnivorous (insectivorous) plants are mainly found in nitrogen deficient soil. To make up the nitrogen deficiency, they have developed insect trapping mechanism in which leaves have taken the shape of a pitcher containing insect digesting proteolytic enzymes. They trap insect and absorb the nitrogen derived from them.

Plant can tolerate a specific amount of micronutrients. A slight lesser amount of it can cause deficiency symptoms and a slight higher amount can cause toxicity. The mineral ion concentration which reduces the dry weight of the tissues by $10 \%$ is called toxic concentration.

This concentration is different for different micronutrients as well as for different plants, e.g., $\mathrm{Mn}^{2+}$ is toxic beyond $600 \mathrm{ogg}^{-1}$ for soyabean and beyond $5300 \mathrm{ogg}^{-1}$ for sunflower.

It has also been observed that the toxicity of one micronutrient causes the deficiency of other nutrients. To overcome such problems, farmers should use these nutrients in prescribed concentration so that the excess uptake of one element do not reduce the uptake of other element.