An element that is labeled as ‘essential’ for plants is characterized by all the following except:
1. Its deficiency cannot be met by supplying some other element
2. It allows normal vegetative growth but does not allow seed set, if absent
3. Its requirement must be specific
4. It must be directly involved in the metabolism of the plant

The minimum amount of requirement for an element to be classified as a macronutrient for plants is:
1. 5 mmole ${\mathrm{kg}}^{-1}$ of dry matter
2. 10 mmole ${\mathrm{kg}}^{-1}$ of dry matter
3. 20 mmole ${\mathrm{kg}}^{-1}$ of dry matter
4. 40 mmole ${\mathrm{kg}}^{-1}$ of dry matter

Which of the following element required by the plants is a micronutrient?

An essential element categorized in elements that can alter the osmotic potential of a cell will be:

Identify the element that is not obtained by terrestrial plants primarily from soil?