What are inorganic nutrients?
Inorganic nutrients are mineral ions that a plant absorbs, in solution, from the soil through its roots. Unlike the sugars a plant makes in photosynthesis, these nutrients cannot be manufactured by the plant itself. They are the raw materials for making proteins, nucleic acids, chlorophyll and many other essential molecules.
Nutrients are grouped by the quantity a plant needs:
- Macronutrients — required in relatively large amounts, e.g. nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca) and sulphur (S).
- Micronutrients (trace elements) — required in very small amounts, e.g. iron (Fe), manganese (Mn), zinc (Zn), copper (Cu) and boron (B).
Roles of key macronutrients
- Nitrogen (N) — used to synthesise amino acids, proteins, nucleic acids and chlorophyll. A shortage causes yellowing of older leaves (chlorosis) and stunted growth.
- Phosphorus (P) — a component of ATP, nucleic acids and phospholipids; promotes healthy root growth and flowering.
- Potassium (K) — activates many enzymes and controls the opening and closing of stomata; it helps maintain ionic balance in cells.
- Magnesium (Mg) — a central component of the chlorophyll molecule, so it is essential for photosynthesis.
- Calcium (Ca) — used in the middle lamella that cements neighbouring cell walls together.
Key idea
Nitrogen and magnesium are both needed for green, healthy leaves — nitrogen for proteins and chlorophyll, magnesium as part of the chlorophyll molecule itself. A shortage of either shows up as chlorosis (yellowing).
Micronutrients and deficiency
Even though micronutrients such as iron are needed only in trace amounts, they are vital — iron is required for the synthesis of chlorophyll (though it is not part of the molecule). A lack of any essential nutrient produces recognisable deficiency symptoms: yellow leaves, poor growth, weak stems or few flowers.
Example
A crop growing on nitrogen-poor soil develops pale yellow lower leaves and grows slowly. Adding a nitrogen fertiliser restores the deep green colour because the plant can again make enough chlorophyll and protein.
Remember
Plants absorb inorganic nutrients as dissolved ions (for example nitrate, NO₃⁻, and potassium, K⁺), not as solid minerals. Water must be present for uptake to occur.