Conditions for N2 fixation : There are following conditions necessary for N2 fixation :
(1) A strong reducing agent like NADPH : It supplies hydrogen to N2.
(2) ATP as source of energy : It provides energy. For fixation of NH3 molecules, 8 ATP molecules are needed.
(3) The enzyme system : Nitrogenase is necessary for N2 fixation.
(4) Compound for trapping ammonia : Ammonia is very toxic and needs to be trapped in the form of amino acids.
(5) Leghaemoglobin : It is O2 scavenger and maintains anaerobic environment otherwise in the presence of O2 the enzyme nitrogenase is toxicated.
Why is that in certain plants deficiency symptoms appear first in younger parts of the plant while in others they do so in mature organs?
2. Die back: It is the withering of stem from apex downward. It is due to the deficiency of copper.
3. Necrosis : It is the death of the tissues. The leaf tips develop dead areas or necrotic areas. It may be also due to Ca, Mg, Ni, Cu and K.
4. Whiptail disease : It occurs in cauliflower. It is due to the deficiency of Mo.
5. Little leaf disease: It is due to the deficiency of Zn. It also causes rosette of apple and peaches.
The purification of water and nutrient salts in hydroponics is very important because of the following reasons:
1. Impure water contains impurities, which will interfere in the growth of plant and make the study for the essntiality difficult.
2. Impurities may be toxic to the plant.
3. Impurities may compete with other minerals.
4. Impurities may inhibit some enzymes.
Therefore, only pure water and nutrients should be taken for hydroponics.