# Mineral Nutrition: Essential Elements

> Mineral nutrition — hydroponics, criteria of essentiality, macro and micronutrients, deficiency symptoms and nitrogen fixation for NEET-UG Biology.

- Canonical URL: https://prepelephant.com/topics/neet-ug/biology/mineral-nutrition-essential-elements
- Exam / course: NEET-UG · Subject: Biology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Mineral Nutrition: Essential Elements", PrepElephant, https://prepelephant.com/topics/neet-ug/biology/mineral-nutrition-essential-elements

## Direct answer

Hydroponics, the soil-less cultivation of plants in nutrient solutions pioneered in the nineteenth century, established that plants need a defined set of essential mineral elements. An element is essential only if it satisfies three criteria of Arnon and Stout: the plant cannot complete its life cycle without it, no other element can replace its role, and it must be directly involved in plant metabolism. About seventeen elements qualify — macronutrients (carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, potassium, calcium and magnesium) needed in large amounts, and micronutrients (iron, manganese, boron, zinc, copper, molybdenum, chlorine and nickel) needed in traces.

## What you must remember

- **Hydroponics:** growing plants in a defined mineral nutrient solution without soil; it proved which elements are indispensable and is used commercially for vegetables.
- **Criteria of essentiality (Arnon and Stout, 1939):** indispensable for completing the life cycle, irreplaceable by another element, and directly involved in plant metabolism.
- **Macronutrients:** carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, potassium, calcium and magnesium — required in amounts greater than 10 millimoles per kilogram of dry matter.
- **Micronutrients:** iron, manganese, boron, zinc, copper, molybdenum, chlorine and nickel — needed in traces, below 10 millimoles per kilogram.
- **Functional roles:** components of organic molecules (N in proteins and nucleic acids, P in ATP and nucleic acids, S in amino acids), enzyme activators (Mg for chlorophyll and many enzymes, Mo for nitrogenase, Zn for various enzymes) and osmotic regulation (K).
- **Deficiency symptoms:** chlorosis — yellowing from lack of chlorophyll — follows deficiency of nitrogen, potassium, magnesium, sulphur, iron, manganese or zinc; necrosis or death of tissue follows potassium, calcium or magnesium deficiency; stunted growth is common.
- **Critical concentration:** the concentration of an element below which growth is retarded; excess of micronutrients above it becomes toxic.
- **Nitrogen fixation:** reduction of atmospheric nitrogen to ammonia by the nitrogenase enzyme of free-living bacteria (such as Azotobacter) and symbiotic forms (Rhizobium in legume root nodules, Frankia in Alnus, Anabaena in Azolla).

## Common confusion

The two lists are the classic confusion — remember that micronutrients are needed only in traces, and that nitrogen is a macronutrient despite heading many mnemonic lists. A second mark-loser is the word essential: abundance is not the test, the Arnon-Stout criteria are. Students also mix chlorosis (yellowing, N-Mg-Fe type deficiencies) with necrosis (tissue death, K-Ca-Mg type); anchor each symptom to its element list. Finally, nitrogenase is oxygen-sensitive, which is why nodules carry leghaemoglobin as an oxygen scavenger.

## Exam-focused takeaway

NEET-UG asks the criteria of essentiality as a three-statement combination, the macro-micro classification in match-the-following, and deficiency symptoms. Hydroponics appears as a one-line definition, and biological nitrogen fixation is tested through Rhizobium, leghaemoglobin and the nitrogenase reaction. Manganese toxicity and the critical-concentration idea surface in assertion-reason items. Memorise the two element lists and pair every symptom with its elements.

## Frequently asked questions

### What is hydroponics?

The technique of growing plants in a nutrient solution without soil, used both to study essential elements and for commercial cultivation.

### State the three criteria of essentiality.

The element must be required for completing the life cycle, must be irreplaceable by another element, and must be directly involved in plant metabolism — the criteria of Arnon and Stout.

### Which elements are macronutrients?

Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, potassium, calcium and magnesium — the nine needed in large quantities.

### What is chlorosis and which deficiencies cause it?

Chlorosis is the yellowing of leaves from loss of chlorophyll, caused by deficiency of elements such as nitrogen, magnesium, iron or manganese.

### What is the role of leghaemoglobin in root nodules?

It is an oxygen scavenger that protects the oxygen-sensitive nitrogenase enzyme while supplying oxygen for respiration in Rhizobium nodules.