In which of the following forms is iron absorbed by plants?

1.	Ferric	2.	Ferrous
3.	Free element	4.	Both ferric and ferrous

During biological nitrogen fixation, inactivation of nitrogenase by oxygen poisoning is prevented by?

1. Leghaemoglobin

2. Xanthophylls

3. Carotene

4. Cytochrome

Minerals known to be required in large amounts for plant growth include:
1. phosphorus, potassium, sulphur, calcium
2. calcium, magnesium, manganese, copper
3. potassium, phosphorus, selenium, boron
4. magnesium, sulphur, iron, zinc

Deficiency symptoms of nitrogen and potassium are visible first in:

1. Senescent leaves

2. Young leaves

3. Roots

4. Buds

The most abundant intracellular cation is:
1. Ca²⁺
2. H⁺
3. K⁺
4. Na⁺

Best defined function of manganese in green plants is :

1. Photolysis of water

2. Calvin cycle

3. Nitrogen fixation

4. Water absorption

An element playing important role in nitrogen fixation is:

1. molybdenum

2. copper

3. manganese

4. zinc

The function of leghemoglobin in the root nodules of legumes is:
1. oxygen removal
2. nodule differentiation
3. expression of nif gene
4. inhibition of nitrogenase activity