BharatNotes Photosynthesis — The Foundation of Life
Photosynthesis is the process by which green plants, algae, and certain bacteria convert light energy into chemical energy stored in glucose. It is the single most important biochemical process on Earth — virtually all food chains begin with photosynthesis.
The Overall Equation
6CO2 + 6H2O + Light Energy --> C6H12O6 + 6O2
Six molecules of carbon dioxide + six molecules of water + light energy yield one molecule of glucose + six molecules of oxygen.
Where Photosynthesis Occurs
| Structure | Role |
|---|---|
| Chloroplast | Organelle where photosynthesis takes place — found in mesophyll cells of leaves |
| Thylakoid membranes | Site of light-dependent reactions — contain chlorophyll and electron transport chain |
| Stroma | Fluid-filled space around thylakoids — site of light-independent reactions (Calvin cycle) |
| Chlorophyll | Green pigment that absorbs light energy — primarily absorbs red and blue wavelengths, reflects green |
Light-Dependent Reactions (Light Reactions)
These reactions occur in the thylakoid membranes and require direct light energy.
| Step | Process |
|---|---|
| Photosystem II (PS II) | Chlorophyll absorbs light; water molecules split (photolysis) releasing oxygen, electrons, and hydrogen ions |
| Electron transport chain | Electrons pass through a series of carriers, releasing energy used to pump H+ ions across the membrane |
| Photosystem I (PS I) | Electrons re-energised by light; transferred to NADP+ reductase |
| ATP synthesis | H+ gradient drives ATP synthase (chemiosmosis) — produces ATP |
| NADPH formation | Electrons combine with NADP+ and H+ to form NADPH |
Products of light reactions: ATP, NADPH, and O2 (released as a byproduct of water splitting)
Light-Independent Reactions (Calvin Cycle / Dark Reactions)
These reactions occur in the stroma and do not directly require light (but depend on ATP and NADPH from light reactions).
| Step | Process |
|---|---|
| Carbon fixation | CO2 is fixed by the enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) to form two molecules of 3-phosphoglycerate (3-PGA) — a 3-carbon compound |
| Reduction | 3-PGA is reduced using ATP and NADPH to form glyceraldehyde-3-phosphate (G3P) |
| Regeneration | Some G3P molecules are used to regenerate RuBP (ribulose-1,5-bisphosphate) for the cycle to continue |
| Sugar synthesis | Remaining G3P molecules are used to synthesise glucose and other organic molecules |
For Prelims: RuBisCO is the most abundant protein on Earth. It catalyses the first step of the Calvin cycle by fixing CO2 into organic carbon. However, RuBisCO can also fix O2 instead of CO2 (photorespiration), which is wasteful — this limitation led to the evolution of C4 and CAM pathways.
C3, C4, and CAM Plants
C3 Plants
| Feature | Detail |
|---|---|
| First stable product | 3-phosphoglycerate (3-PGA) — a 3-carbon compound |
| Carbon fixation enzyme | RuBisCO |
| Photorespiration | Significant — RuBisCO fixes O2 about 20-25% of the time, wasting energy |
| Optimal temperature | 15-25 degrees C |
| Percentage of plants | Approximately 95% of all plant species |
| Examples | Wheat, rice, barley, soybean, potato, most trees |
| Limitation | Inefficient in hot, dry conditions due to high photorespiration |
C4 Plants
| Feature | Detail |
|---|---|
| First stable product | Oxaloacetate (OAA) — a 4-carbon compound |
| Carbon fixation enzyme | PEP carboxylase (initial fixation); RuBisCO (in bundle sheath cells) |
| Photorespiration | Minimal — CO2 concentrated in bundle sheath cells prevents O2 fixation |
| Anatomy | Kranz anatomy — distinct mesophyll and bundle sheath cells with specialised functions |
| Optimal temperature | 30-40 degrees C |
| Percentage of plants | Approximately 3-4% of plant species |
| Examples | Maize, sugarcane, sorghum, millets, amaranth |
| Advantage | Higher photosynthetic efficiency in hot, high-light environments |
CAM Plants (Crassulacean Acid Metabolism)
| Feature | Detail |
|---|---|
| Strategy | Temporal separation — stomata open at night (CO2 uptake), close during day (water conservation) |
| Night process | CO2 fixed by PEP carboxylase into malic acid, stored in vacuoles |
| Day process | Malic acid decarboxylated to release CO2, which enters Calvin cycle with stomata closed |
| Optimal conditions | Hot, arid environments (35-45 degrees C) |
| Examples | Cacti, succulents, pineapple, agave, some orchids |
| Advantage | Extremely water-efficient — up to 10x more water-use efficient than C3 plants |
| Limitation | Slow growth rate due to limited CO2 fixation capacity |
Comparison Table
| Parameter | C3 | C4 | CAM |
|---|---|---|---|
| CO2 fixation | Calvin cycle only | Mesophyll + bundle sheath | Night fixation + day Calvin cycle |
| Enzyme | RuBisCO | PEP carboxylase + RuBisCO | PEP carboxylase + RuBisCO |
| Photorespiration | High (20-25%) | Very low | Negligible |
| Water use efficiency | Lowest | Moderate | Highest |
| Stomata | Open during day | Open during day | Open at night |
| Growth rate | Moderate | Fast | Slow |
For Mains: The C3/C4/CAM classification has direct agricultural implications. As global temperatures rise due to climate change, C4 crops (maize, sorghum, millets) may gain advantage over C3 staples (wheat, rice). Research is underway (C4 Rice Project) to engineer C4 photosynthetic pathways into rice — this could increase rice yield by 50% while using less water.
Plant Hormones (Phytohormones)
Plant hormones are chemical messengers produced in tiny amounts that regulate growth, development, and responses to environmental stimuli.
The Five Major Plant Hormones
| Hormone | Site of Production | Key Functions |
|---|---|---|
| Auxin (IAA) | Shoot tips, young leaves, developing seeds | Promotes cell elongation; apical dominance; phototropism (bending toward light); gravitropism (root growth downward); fruit development; root initiation |
| Gibberellins (GA) | Root and shoot tips, young leaves, seeds | Promotes stem elongation; seed germination (breaks dormancy); flowering in long-day plants; fruit development; bolting |
| Cytokinins | Root tips, developing seeds, fruits | Promotes cell division; delays senescence (leaf aging); promotes shoot growth in tissue culture; counteracts apical dominance (promotes lateral bud growth) |
| Ethylene | Ripening fruits, aging tissues, stressed cells | Fruit ripening; leaf and flower abscission (shedding); senescence; triple response in seedlings; stress responses |
| Abscisic Acid (ABA) | Leaves, stems, roots, green fruits | Stomatal closure during drought stress; seed dormancy; inhibits growth; stress hormone — responds to drought, salinity, cold |
Practical Applications of Plant Hormones
| Application | Hormone Used | Detail |
|---|---|---|
| Rooting powder | Synthetic auxin (IBA, NAA) | Applied to stem cuttings to promote root formation in vegetative propagation |
| Weed control | Synthetic auxin (2,4-D) | Selective herbicide — kills broadleaf weeds in cereal crops without harming the crop |
| Fruit ripening | Ethylene (ethephon) | Used to ripen bananas, mangoes, and tomatoes uniformly for commercial purposes |
| Seedless grapes | Gibberellin | Applied to grape clusters to produce larger, seedless fruits |
| Anti-lodging | Growth retardants (inhibit GA) | Used in wheat to produce shorter, sturdier stems that resist lodging |
| Shelf life extension | Cytokinin application | Delays senescence in cut flowers and harvested vegetables |
For Prelims: Ethylene is a gaseous hormone. It is responsible for fruit ripening — this is why placing a ripe banana next to unripe fruits hastens their ripening (ethylene diffuses through the air). ABA is called the "stress hormone" because it is produced in response to drought, salinity, and cold stress, causing stomatal closure to conserve water.
Plant Nutrition
Essential Macro and Micronutrients
| Category | Elements | Function |
|---|---|---|
| Primary macronutrients | Nitrogen (N), Phosphorus (P), Potassium (K) | N: amino acids, proteins, chlorophyll; P: ATP, nucleic acids, root development; K: enzyme activation, stomatal regulation, disease resistance |
| Secondary macronutrients | Calcium (Ca), Magnesium (Mg), Sulphur (S) | Ca: cell wall structure; Mg: central atom of chlorophyll; S: amino acids (cysteine, methionine) |
| Micronutrients | Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo), Chlorine (Cl), Nickel (Ni) | Required in trace amounts; essential for enzyme function, electron transport, and various metabolic processes |
Nitrogen Fixation
| Type | Mechanism | Organisms/Examples |
|---|---|---|
| Biological — symbiotic | Rhizobium bacteria in root nodules of legumes fix atmospheric N2 into NH3 using nitrogenase enzyme | Rhizobium-legume association (soybean, chickpea, lentils, groundnut) |
| Biological — free-living | Free-living soil bacteria fix nitrogen independently | Azotobacter, Clostridium, Azospirillum |
| Biological — associative | Bacteria associated with plant roots (not in nodules) | Azospirillum with grass roots; Acetobacter with sugarcane |
| Cyanobacteria | Blue-green algae fix nitrogen in paddy fields and soil crusts | Anabaena, Nostoc — important in rice cultivation |
| Industrial (Haber-Bosch) | High temperature (400-500 degrees C) and pressure to convert N2 + H2 into NH3 | Basis of synthetic fertiliser production — consumes 1-2% of global energy |
For Prelims: Biological nitrogen fixation requires the enzyme nitrogenase, which is inactivated by oxygen. Legumes provide an anaerobic environment in root nodules through leghemoglobin (a pink-coloured protein similar to hemoglobin that binds oxygen). The Rhizobium-legume symbiosis can fix 50-300 kg nitrogen per hectare per year.
Crop Improvement Methods
Traditional Methods
| Method | Description | Examples |
|---|---|---|
| Selection | Identifying and propagating plants with desirable traits from a natural population | Pure line selection, mass selection |
| Hybridisation | Cross-pollination between two genetically different parent plants to combine desirable traits | Hybrid rice (e.g., KRH-2), hybrid maize, hybrid cotton |
| Mutation breeding | Using physical (X-rays, gamma rays, UV) or chemical (EMS, colchicine) mutagens to create genetic variation | Groundnut varieties (TG series from BARC), castor, jute |
| Polyploidy | Inducing chromosome doubling using colchicine to create plants with larger cells, organs, and higher yield | Seedless watermelon (triploid), bread wheat (hexaploid), triticale (wheat x rye cross) |
| Introduction | Importing plant varieties from other regions and adapting them | Soybean (introduced from China), sunflower (from Russia) |
Modern Biotechnological Methods
| Method | Description | Application |
|---|---|---|
| Tissue culture | Growing plants from small tissue pieces (explants) on nutrient media under sterile conditions | Mass propagation of banana, orchids, cardamom; virus-free planting material |
| Somatic hybridisation | Fusing protoplasts (cells without walls) from two different species to create hybrid plants | Pomato (potato + tomato) — experimental; disease-resistant citrus varieties |
| Genetic engineering | Direct insertion of specific genes into plant genome using recombinant DNA technology | Bt cotton, Golden Rice, herbicide-tolerant crops |
| Marker-assisted selection (MAS) | Using DNA markers linked to desirable traits to speed up conventional breeding | Disease-resistant rice varieties; drought-tolerant wheat |
| Genome editing (CRISPR-Cas9) | Precise editing of plant DNA at specific locations | Improved nutritional quality, disease resistance, drought tolerance — emerging technology |
GM Crops in India
Bt Cotton — India's Only Commercially Approved GM Crop
| Feature | Detail |
|---|---|
| Approved | 2002 (first GM crop commercially cultivated in India) |
| Technology | Contains Cry1Ac gene from Bacillus thuringiensis (Bt) — produces a protein toxic to bollworm larvae |
| Adoption | Over 95% of India's cotton area now uses Bt cotton |
| Impact on yield | Cotton production roughly doubled from approximately 13.6 million bales (2002) to over 35 million bales |
| Concerns | Pink bollworm has developed resistance in several regions; increased dependence on herbicides for secondary pests; farmer debt issues due to high seed costs |
GM Mustard (DMH-11) Controversy
| Aspect | Detail |
|---|---|
| Full name | Dhara Mustard Hybrid-11 |
| Developed by | Centre for Genetic Manipulation of Crop Plants, Delhi University |
| Technology | Contains barnase and barstar genes from Bacillus amyloliquefaciens enabling hybrid seed production in mustard |
| GEAC clearance | Genetic Engineering Appraisal Committee (GEAC) recommended environmental release in October 2022 |
| Supreme Court | Split verdict — one judge invalidated approval citing procedural flaws and public interest concerns; the other upheld it. Matter referred to a larger bench |
| Opposition | Groups like Sarson Satyagraha argue it threatens India's 6,000-year mustard cultivation heritage and genetic diversity |
| Support | Proponents argue India imports 55-60% of edible oil; GM mustard hybrids could significantly boost domestic oilseed production |
For Mains: The GM mustard debate encapsulates the broader tension between food security (India's edible oil import dependence of 55-60%) and biosafety concerns (impact on biodiversity, non-target organisms, indigenous crop varieties). UPSC questions on GM crops typically require balanced analysis of both scientific evidence and socio-economic concerns.
Regulatory Framework for GM Crops in India
| Body | Role |
|---|---|
| GEAC | Genetic Engineering Appraisal Committee under MoEFCC — apex body for approval of GM organisms for environmental release |
| RCGM | Review Committee on Genetic Manipulation under DBT — monitors ongoing research |
| IBSC | Institutional Biosafety Committee — every institution working with GMOs must have one |
| Environment Protection Act, 1986 | Legal framework under which GM crop regulations operate |
| Cartagena Protocol | International framework on biosafety — India is a signatory |
Tissue Culture and Micropropagation
Process
| Stage | Description |
|---|---|
| Explant selection | Small piece of plant tissue (shoot tip, leaf, meristem) selected from a disease-free mother plant |
| Sterilisation | Explant surface-sterilised to remove microbial contamination |
| Inoculation | Explant placed on sterile nutrient medium (Murashige and Skoog medium) containing plant hormones |
| Callus formation | Undifferentiated mass of cells (callus) develops from the explant |
| Organogenesis | Manipulation of auxin-to-cytokinin ratio induces shoot or root formation |
| Plantlet development | Complete plantlet with roots and shoots develops |
| Hardening | Plantlet gradually acclimatised to normal conditions before field transfer |
Applications in India
| Application | Detail |
|---|---|
| Banana micropropagation | Tissue-cultured banana plantlets widely used — disease-free, uniform, high-yielding (Grand Naine variety) |
| Cardamom | Tissue culture used to multiply high-yielding cardamom varieties |
| Orchids | Commercial orchid production through tissue culture in northeast India |
| Sugarcane | Disease-free sugarcane setts through meristem culture |
| Bamboo | Mass propagation of superior bamboo varieties for National Bamboo Mission |
| Forest trees | Teak, eucalyptus, and other commercially important trees |
For Prelims: Totipotency is the ability of a single plant cell to develop into a complete plant. This property forms the scientific basis of tissue culture. The Murashige and Skoog (MS) medium is the most commonly used nutrient medium for plant tissue culture.
Organic Farming in India
Paramparagat Krishi Vikas Yojana (PKVY)
| Feature | Detail |
|---|---|
| Launched | 2015, under the National Mission for Sustainable Agriculture |
| Objective | Promote organic farming through cluster-based approach |
| Financial assistance | Rs 31,500 per hectare over 3 years |
| Cluster approach | Farmers mobilised in groups (initially 20 hectares each; now 500-1,000 farmers per cluster) |
| Coverage | Government funding of Rs 50,000 per hectare for a 3-year period covering inputs, certification, and marketing |
| Target | Additional 6,00,000 hectares under organic farming by 2025-26 |
| Budget (2025) | Over Rs 800 crore allotted; 60% directly for farmer input costs (organic manure, seeds, bio-pesticides) |
Zero Budget Natural Farming (ZBNF)
| Feature | Detail |
|---|---|
| Concept | Farming method that eliminates external purchased inputs — using only natural, on-farm resources |
| Key practices | Jeevamrutha (microbial culture), Beejamrutha (seed treatment), mulching, waaphasa (moisture management) |
| Propagated by | Subhash Palekar — agricultural scientist from Maharashtra |
| Government support | Promoted under PKVY; Andhra Pradesh's Community Managed Natural Farming (CMNF) programme is the largest ZBNF initiative covering millions of farmers |
| Cost | Approximately Rs 1,000 per acre — making it extremely affordable for marginal farmers |
| Criticism | Limited peer-reviewed scientific evidence on yield comparisons with conventional farming; scalability concerns |
India's Organic Farming Statistics
| Metric | Detail |
|---|---|
| Organic farming area | Approximately 5.9 million hectares (including cultivation and wild harvest collection) |
| Global ranking | India ranks 1st in number of organic farmers and 5th in organic cultivation area globally |
| Organic exports | Approximately USD 700-800 million annually |
| Sikkim | Became India's first fully organic state in 2016 |
| Key organic crops | Oilseeds, sugarcane, tea, cereals, millets, cotton, spices, pulses, coffee |
Precision Agriculture
What Is Precision Agriculture?
Precision agriculture uses technology to optimise crop management at a fine spatial and temporal scale — applying the right input, at the right place, at the right time, in the right amount.
Key Technologies
| Technology | Application in Agriculture |
|---|---|
| Remote sensing (satellites) | Crop health monitoring via NDVI (Normalised Difference Vegetation Index); drought assessment; crop area estimation; ISRO's RISAT and Resourcesat used for agricultural monitoring |
| Drones (UAVs) | Crop spraying (pesticides, fertilisers); crop health surveillance; field mapping; India approved drone spraying of pesticides in 2021 under Drone Rules |
| IoT sensors | Soil moisture monitoring; weather stations; automated irrigation systems; nutrient monitoring |
| GPS-guided machinery | Precision planting, precision fertiliser application, variable-rate technology |
| AI and machine learning | Crop disease detection from images; yield prediction; pest outbreak forecasting |
| GIS mapping | Soil fertility mapping; land use classification; precision nutrient management |
Government Initiatives
| Initiative | Detail |
|---|---|
| Kisan Drone | Government promoting drone use for crop assessment, spraying, and land record digitisation |
| Digital Agriculture Mission | Rs 2,817 crore mission for digital crop surveys, soil health monitoring, and farmer registry |
| Soil Health Card scheme | Testing soil samples and providing nutrient recommendations — supports precision fertiliser application |
| Agri-Stack | Digital infrastructure for agriculture — farmer IDs, land records, crop surveys linked to create a unified digital ecosystem |
Plant Diseases and Integrated Pest Management
Major Crop Diseases in India
| Disease | Crop | Causal Agent | Impact |
|---|---|---|---|
| Blast | Rice | Magnaporthe oryzae (fungus) | Major disease worldwide; can cause 70-80% yield loss |
| Rust | Wheat | Puccinia species (fungus) | Three types — stem rust, leaf rust, stripe rust; can devastate wheat crop |
| Late blight | Potato, Tomato | Phytophthora infestans (oomycete) | Caused the Irish Potato Famine (1845-49); still a major global threat |
| Wilt | Cotton, Chickpea, Banana | Fusarium species (fungus) | Panama disease (Fusarium wilt) threatens global banana production |
| Citrus canker | Citrus fruits | Xanthomonas citri (bacteria) | Causes lesions on fruits and leaves; reduces marketability |
| Tungro | Rice | Rice Tungro Virus (transmitted by green leafhopper) | Major viral disease of rice in South and Southeast Asia |
| Mosaic | Various crops | Multiple viruses | Yellow mosaic of soybean, tobacco mosaic virus — reduce photosynthesis |
Integrated Pest Management (IPM)
| Component | Methods |
|---|---|
| Cultural control | Crop rotation, intercropping, resistant varieties, adjusting planting dates, field sanitation |
| Biological control | Natural predators (ladybird beetles for aphids), parasitoids (Trichogramma wasps for stem borers), microbial pesticides (Bt spray, Trichoderma fungi, Beauveria bassiana) |
| Mechanical control | Light traps, pheromone traps, yellow sticky traps, hand picking of pests |
| Chemical control | Last resort — targeted use of pesticides at economic threshold level; neem-based bio-pesticides preferred |
| Genetic resistance | Breeding crop varieties with built-in pest resistance — reduces need for chemical pesticides |
For Mains: IPM is the recommended approach under India's National Policy on Farmers (2007) and aligns with organic farming goals. The emphasis is on reducing chemical pesticide dependence while maintaining crop productivity. India is one of the largest consumers of pesticides in Asia, with concerns about pesticide residues in food and environmental contamination.
Seed Technology
Types of Seeds
| Category | Description |
|---|---|
| Nucleus seed | Produced by the original plant breeder — genetically purest form; limited quantity |
| Breeder seed | Produced from nucleus seed under supervision of plant breeder — golden/yellow tag |
| Foundation seed | Produced from breeder seed under supervision of seed certification agency — white tag |
| Certified seed | Produced from foundation seed; quality tested and certified — blue tag (azure blue) |
| Truthfully labelled seed | Not formally certified but labelled with variety name and germination percentage — opal green tag |
Hybrid Seeds vs. Open-Pollinated Varieties
| Parameter | Hybrid Seeds | Open-Pollinated Varieties (OPVs) |
|---|---|---|
| Development | Cross between two genetically distinct inbred lines | Developed through natural selection or open pollination |
| Vigour | Exhibit heterosis (hybrid vigour) — higher yield, uniformity | Stable performance across generations |
| Seed saving | Farmers cannot save seeds — F2 generation shows segregation and yield decline | Farmers can save and replant seeds |
| Cost | Expensive — must be purchased each season | Low cost — can be farm-saved |
| Dependence | Creates dependence on seed companies | Promotes farmer autonomy |
| Examples | Hybrid maize, hybrid rice, Bt cotton (hybrid) | Traditional rice varieties, desi wheat varieties |
Seed Legislation in India
| Law/Bill | Detail |
|---|---|
| Seeds Act, 1966 | Current governing law — regulates seed quality through voluntary certification |
| Seeds Bill, 2004 | Proposed replacement — mandates compulsory registration of all seed varieties (including GM and imported); provides farmer compensation mechanism if registered seeds fail; registration valid for 15 years (annual/biennial crops) and 18 years (perennials); lapsed and not yet passed |
| Protection of Plant Varieties and Farmers' Rights Act, 2001 | Protects breeders' rights while safeguarding farmers' rights to save, use, exchange, and share seeds |
| Seed certification agencies | State Seed Certification Agencies operate under Seeds Act; Seeds Bill proposed private accreditation |
For Prelims: Under the Indian seed certification system, breeder seed has a golden/yellow tag, foundation seed has a white tag, and certified seed has a blue tag. The Protection of Plant Varieties and Farmers' Rights Act (PPV&FR), 2001 is India's sui generis system for plant variety protection under TRIPS, which uniquely protects farmers' rights alongside breeders' rights.
Recent Developments (2024–2026)
CSIR — World's First Pink Bollworm-Resistant GM Cotton (2024–25)
CSIR-National Botanical Research Institute (NBRI) developed the world's first genetically modified cotton variety fully resistant to pink bollworm — a major pest causing annual crop losses exceeding ₹5,000 crore in India. This achievement, announced in 2024–25, builds on India's Bt cotton technology and demonstrates CSIR's capability in agricultural biotechnology. India is the world's third-largest cotton producer, and pink bollworm resistance development is a significant plant biology-agriculture convergence.
UPSC angle: This is a verifiable, India-specific GM crop development — relevant for GS3 questions on agricultural biotechnology, food security, and GM crop ethics.
Millets — India's Scientific and Policy Push (2023 IYM Legacy, 2024)
Following India's International Year of Millets (IYM 2023) initiative, the government continued promoting millet cultivation and consumption in 2024 through PM-PRANAM (Promotion of Alternate Nutrients for Agriculture Management) and PM-POSHAN schemes. ICAR released new high-yield, climate-resilient millet varieties. Research demonstrated that millets — jowar, bajra, ragi — are nutritionally superior to polished rice/wheat in fibre, micronutrients, and glycaemic index, reducing diabetes and cardiovascular disease risk.
UPSC angle: India's millet push connects plant biology (nutritional properties), agriculture (sustainable farming), and health policy — a high-frequency GS3 integrated theme.
Key Terms for UPSC
| Term | Definition |
|---|---|
| Photosynthesis | Process by which plants convert CO2 and H2O into glucose and O2 using light energy |
| RuBisCO | Ribulose-1,5-bisphosphate carboxylase/oxygenase — the most abundant protein on Earth; fixes CO2 in Calvin cycle |
| C4 photosynthesis | Pathway using PEP carboxylase for initial CO2 fixation, concentrating CO2 in bundle sheath cells to minimise photorespiration |
| CAM | Crassulacean Acid Metabolism — plants fix CO2 at night and use it for Calvin cycle during the day; extremely water-efficient |
| Auxin | Plant hormone promoting cell elongation, phototropism, and root initiation |
| Nitrogen fixation | Conversion of atmospheric N2 to NH3 — biologically by Rhizobium in legume root nodules, or industrially by Haber-Bosch process |
| Bt cotton | Genetically modified cotton containing Cry1Ac gene from Bacillus thuringiensis — India's only approved GM crop |
| DMH-11 | Dhara Mustard Hybrid-11 — genetically modified mustard variety; approval status contested in Supreme Court |
| PKVY | Paramparagat Krishi Vikas Yojana — government scheme promoting organic farming in clusters |
| IPM | Integrated Pest Management — combining biological, cultural, mechanical, and chemical methods with minimal pesticide use |
| GEAC | Genetic Engineering Appraisal Committee — apex body for approving environmental release of GMOs in India |
Exam Strategy
Prelims Focus: C3/C4/CAM differences and examples, plant hormone functions (especially auxin, ethylene, ABA), nitrogen fixation organisms, Bt cotton gene and mechanism, seed tag colours, GEAC function, tissue culture concepts (totipotency), macro and micronutrients.
Mains Connections: Link GM crop debate to food security vs. biosafety (GS3). Connect organic farming to sustainable agriculture and soil health (GS3). Relate precision agriculture to technology-driven agricultural transformation. Discuss plant biotechnology's role in addressing climate change impacts on crop productivity.
Essay Potential: "Feeding a billion while protecting biodiversity — India's agricultural biotechnology dilemma" covering the GM crop debate, organic farming potential, and the need for balanced policy.
