With the help of examples describe the classification of essential elements based on the function they perform.

Essential elements are involved in performing variety of functions in plants. Some of the major functions are enlisted below
(i) Frame work elements Essential elements as components of biomolecules and hence are structural elements of the cell. Carbon, hydrogen and oxygen are considered as framework elements because they constitute carbohydrates which form cell wall.
(ii) Protoplasmic elements N, P and S are considered as protoplasmic elements as they form protoplasm along with $\mathrm{C},\mathrm{H}$ and oxygen.
(iii) Catalytic enzyme Essential elements that activates or inhibit enzymes, i.e., without the presence of these elements some enzymes can not function e.g., ${\mathrm{Mg}}^{2+}$ acts as an activator for both ribulose biphosphate carboxylase oxygenase (Rubisco) and phosphoenol pyruvate carboxylase (PEP carboxylase).
Both are the critical enzymes involved in photosynthetic carbon fixation in plants.
(iv) Balancing elements Elements counteract the toxic effect of other minerals by causing ionic balance (e.g., calcium, magnesium and potassium).
(v) Influencing on the osmotic pressure of the cell Some essential elements alters the osmotic potential of the cell. Plant cells contain dissolved mineral elements in the cell sap influencing osmotic pressure of the cell, e.g., $\mathrm{K}$ is involved in opening and closing of stomata.