Mineral Nutrition: Mobility and Classification - Practice Questions & MCQ

Essential elements can also be grouped into four broad categories on the basis of their diverse functions. These categories are:

1. Essential elements as components of biomolecules and hence structural elements of cells (e.g., carbon, hydrogen, oxygen and nitrogen).

2. Essential elements that are components of energy-related chemical compounds in plants (e.g., magnesium in chlorophyll and phosphorus in ATP).

3. Essential elements that activate or inhibit enzymes, for example, Mg2+ is an activator for both ribulose bisphosphate carboxylase oxygenase and phosphoenolpyruvate carboxylase, both of which are critical enzymes in photosynthetic carbon fixation; Zn2+ is an activator of alcohol dehydrogenase and Mo of nitrogenase during nitrogen metabolism. 

4.  Some essential elements can alter the osmotic potential of a cell. Potassium plays an important role in the opening and closing of stomata.
 

Essential elements can also be divided on the basis of their mobility within a plant and their tendency to translocate within the plant during deficiencies:

• Once inside plants, nutrients are transported to where they are needed, typically to growing points. 
• Once incorporated by the plant, some elements can be immobile while others can be remobilized. 
• Immobile elements such as Calcium, Sulphur, Boron, Copper, and Iron essentially get locked in place and that is where they stay.
• Since immobile elements do not easily move within the plant when deficiency symptoms occur they show up in new growth, that is, their deficiency is seen in the young parts first.
• When mobile elements become scarce, they can be used from older growth and moved to where they are most needed, causing deficiency symptoms in older growth.