Which essential element is important for the opening and closing of stomata in higher plants?
1. Calcium
2. Sodium
3. Potassium
4. Phosphorus

Nitrogen fixation means:
1. releasing nitrogen from dead and decaying materials.
2. conversion of nitrite to nitrate.
3. conversion of nitrate to nitrite.
4. conversion of nitrogen gas into ammonia.

Majority of the nutrients that are essential for the growth and development of plants become available to the roots due to:
1. Microbial actions in the soil
2. Wet deposition from the atmosphere
3. Addition of fertilizers
4. Weathering and breakdown of rocks

A symptom common to the deficiency of Ca, Mg, Cu and K in plants is:
1. Chlorosis
2. Inhibition of cell division
3. Necrosis
4. Delay in flowering

Plants can be grown in (Select the incorrect option)
1. Soil with essential nutrients
2. Water with essential nutrients
3. Either water or soil with essential nutrients
4. Water or soil without essential nutrients

With regard to the Biological Nitrogen Fixation by Rhizobium in association with soyabean, which one of the following statement/statements does not hold true?
1. Nitrogenase may require oxygen for its functioning .
2. Nitrogenase is MO-Fe protein.
3. Leg-hemoglobin is a pink coloured pigment.
4. Nitrogenase helps to convert ${\mathrm{N}}_2$ gas into two molecules of ammonia. 

Which one of the following statements can best explain the term critical concentration of an essential element?
1. Essential element concentration below which plant growth is retarded.
2. Essential element concentration below which plant growth becomes stunted.
3. Essential element concentration below which plant remains in the vegetative phase.
4. None of the above

Name the amino acid from which 17 other amino acids are formed by transamination in plants?