Mineral Nutrition – NEET 2025 Complete Notes (With Diagrams & PYQs)
Mineral Nutrition – Introduction and Essential Elements
Plants, unlike animals, synthesize their own food through photosynthesis, yet they also require minerals from the soil to grow and function properly. These minerals play a vital role in plant metabolism, enzyme activation, and structural development. The study of how plants absorb, transport, and utilize these inorganic nutrients is known as mineral nutrition.
According to NCERT, mineral nutrition is defined as “the study of the source, mode of absorption, transport, and function of inorganic nutrients in plants.” Plants absorb various ions such as nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), and iron (Fe) from the soil, which are essential for growth and development.
There are 17 essential elements required for normal plant growth, classified into three groups:
(A) Macronutrients – required in large amounts:
Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Potassium (K), Sulphur (S), Calcium (Ca), and Magnesium (Mg).
(B) Micronutrients – required in small amounts:
Iron (Fe), Manganese (Mn), Copper (Cu), Zinc (Zn), Boron (B), Molybdenum (Mo), Chlorine (Cl), and Nickel (Ni).
(C) Beneficial Elements – not essential but helpful for certain plants:
Sodium (Na), Silicon (Si), Cobalt (Co), and Selenium (Se).
A helpful mnemonic to recall macronutrients is “CHOPKINS CaFe Mg.”
Mineral Nutrition – Criteria for Essentiality and Deficiency Symptoms
In 1939, Arnon and Stout proposed three main criteria to determine whether an element is essential for plants:
-
A plant cannot complete its life cycle without that element.
-
The element cannot be replaced by any other element.
-
It plays a direct and specific role in the plant’s metabolism.
In simple terms, an essential element is both irreplaceable and indispensable for plant growth.
Functions and Deficiency Symptoms of Essential Elements
| Element | Function | Deficiency Symptom |
|---|---|---|
| Nitrogen (N) | Protein and chlorophyll synthesis | Chlorosis in older leaves |
| Phosphorus (P) | Component of ATP and nucleic acids | Poor root growth |
| Potassium (K) | Regulation of stomatal movement | Yellowing at leaf margins |
| Calcium (Ca) | Cell wall formation | Death of meristematic regions |
| Magnesium (Mg) | Part of chlorophyll molecule | Interveinal chlorosis |
| Iron (Fe) | Chlorophyll synthesis | Yellowing of young leaves |
| Zinc (Zn) | Auxin synthesis | Little leaf disease |
| Copper (Cu) | Enzyme activation | Dieback of shoots |
| Boron (B) | Pollen germination | Death of root tip |
| Molybdenum (Mo) | Nitrogen fixation | Whiptail in cauliflower |
Common Deficiency Symptoms
| Symptom | Cause | Example Elements |
|---|---|---|
| Chlorosis | Lack of chlorophyll | N, Mg, Fe, Zn |
| Necrosis | Death of tissues | Ca, K |
| Inhibition of cell division | Reduced growth | N, K, S, Mo |
| Stunted growth | Poor elongation | N, P, K |
| Premature leaf fall | Early senescence | P |
| Purple leaves | Anthocyanin accumulation | P |
Key Note:
-
Chlorosis = yellowing of leaves due to chlorophyll loss.
-
Necrosis = death of plant tissues.
Mineral Nutrition – Hydroponics and Nitrogen Metabolism
Hydroponics (Soilless Cultivation)
Hydroponics is a technique of growing plants without soil, using a nutrient-rich solution that provides all essential minerals. It helps identify which elements are necessary for plant growth by supplying controlled nutrients.
This method demonstrates that soil acts only as a reservoir for minerals, while the actual nutrient absorption depends on water and ions in solution.
Example: Hydroponic systems are used to cultivate lettuce, tomatoes, and herbs under laboratory or commercial conditions.
Nitrogen Metabolism – Overview
Nitrogen is an essential component of amino acids, proteins, chlorophyll, and nucleic acids. Plants absorb it mainly as nitrate (NO₃⁻) and ammonium (NH₄⁺) ions from the soil.
The nitrogen cycle includes several key processes:
-
Nitrogen Fixation – Conversion of atmospheric N₂ into ammonia (NH₃).
-
Nitrification – Oxidation of ammonia to nitrite (NO₂⁻) and then to nitrate (NO₃⁻).
-
Assimilation – Incorporation of nitrates into amino acids and proteins.
-
Ammonification – Decomposition of organic nitrogen compounds back into NH₃.
-
Denitrification – Reduction of nitrates to nitrogen gas (N₂), returning it to the atmosphere.
Each step ensures that nitrogen continuously cycles between the soil, plants, and the air, maintaining ecological balance.
Mineral Nutrition – Biological Nitrogen Fixation and Key Enzymes
Biological Nitrogen Fixation
Nitrogen fixation is primarily carried out by prokaryotic organisms such as bacteria and cyanobacteria that convert atmospheric nitrogen (N₂) into ammonia (NH₃). This process can be either symbiotic or free-living.
| Type | Organisms | Examples |
|---|---|---|
| Free-living | Aerobic or anaerobic bacteria | Azotobacter, Clostridium |
| Symbiotic | Bacteria living in root nodules | Rhizobium in legumes |
| Cyanobacteria | Photosynthetic nitrogen fixers | Nostoc, Anabaena in rice fields |
Root Nodule Formation
-
Rhizobium bacteria recognize root hairs of legumes and form an infection thread that penetrates into the root cortex.
-
Nodules are formed containing the enzyme nitrogenase.
-
Nitrogenase catalyzes the conversion of N₂ → NH₃ under anaerobic conditions.
-
Leghaemoglobin in nodules binds oxygen, maintaining low O₂ levels for the enzyme to function efficiently.
Simplified Reaction:
N₂ + 8H⁺ + 8e⁻ + 16ATP → 2NH₃ + H₂ + 16ADP + 16Pi
Important Enzymes and Cofactors
| Enzyme | Function | Cofactor |
|---|---|---|
| Nitrogenase | N₂ → NH₃ | Fe + Mo |
| Nitrate Reductase | NO₃⁻ → NO₂⁻ | Molybdenum |
| Nitrite Reductase | NO₂⁻ → NH₃ | Iron |
Key Concept:
The Fe-Mo cofactor (FeMoCo) is essential for biological nitrogen fixation.
Mineral Nutrition – Biofertilizers, NEET PYQs, and Summary
Biofertilizers – Natural Enhancers of Soil Fertility
Biofertilizers are living microorganisms that improve soil fertility by increasing the availability of nutrients to plants. They are an eco-friendly and sustainable alternative to chemical fertilizers.
| Type | Examples | Function |
|---|---|---|
| Nitrogen-fixing | Rhizobium, Azospirillum | Add atmospheric nitrogen to soil |
| Phosphate-solubilizing | Bacillus megaterium | Release phosphate for plant use |
| Mycorrhizal fungi | Glomus species | Enhance water and mineral absorption |
Key Concept:
Biofertilizers promote long-term soil health and reduce dependency on synthetic fertilizers.
Frequently Asked NEET Questions (2017–2024)
| Year | Question | Answer |
|---|---|---|
| 2024 | Enzyme in biological N₂ fixation | Nitrogenase |
| 2023 | Cofactor in nitrate reductase | Molybdenum |
| 2021 | Free-living nitrogen fixer | Azotobacter |
| 2020 | Symbiotic nitrogen fixer | Rhizobium |
| 2019 | Function of leghaemoglobin | Maintains anaerobic condition |
| 2018 | Elements causing chlorosis | N, Mg, Fe, Zn |
Quick Summary Table
| Concept | Keyword | Key Point |
|---|---|---|
| Essential Elements | 17 elements | CHOPKINS CaFe Mg + Micronutrients |
| Nitrogenase | Enzyme | Anaerobic, FeMoCo cofactor |
| Deficiency | Symptoms | Chlorosis, Necrosis, Stunted growth |
| Hydroponics | Technique | Growth in nutrient solution |
| Rhizobium | Symbiosis | Forms nodules in legumes |
Conclusion
Mineral Nutrition explains the essential connection between soil minerals and plant life. Understanding the absorption, transport, and utilization of these nutrients helps decode many physiological processes in plants. Every atom of nitrogen in living organisms ultimately originates from microbial nitrogen fixation.
For NEET preparation, focus on essential elements, deficiency symptoms, and nitrogen cycle enzymes, and practice all previous-year NCERT-based questions.
Comments
Post a Comment