BharatNotes Why this chapter matters for UPSC: Photosynthesis is the foundation of all food chains and the global carbon cycle — both core UPSC environment topics. Plant life processes connect to forest conservation, climate change, ecosystem services, and India's biodiversity policy. The role of forests as carbon sinks is a major climate negotiation issue.
PART 1 — Quick Reference Tables
| Life Process | Definition | Organ/Structure |
|---|---|---|
| Photosynthesis | Synthesis of food using CO₂, water, and sunlight | Leaves (chloroplasts) |
| Respiration | Breaking down glucose to release energy | All living cells (mitochondria) |
| Transpiration | Loss of water vapour through stomata | Leaves (stomata) |
| Transport (water) | Absorption and movement of water and minerals | Roots → xylem → leaves |
| Transport (food) | Movement of synthesised food to all parts | Phloem (leaves → all parts) |
| Reproduction | Sexual (seed) and asexual (vegetative) | Flowers, bulbs, runners, rhizomes |
| Photosynthesis — Key Facts | Detail |
|---|---|
| Raw materials | Carbon dioxide (CO₂) + Water (H₂O) |
| Energy source | Sunlight (absorbed by chlorophyll) |
| Products | Glucose (C₆H₁₂O₆) + Oxygen (O₂) |
| Overall equation | 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂ |
| Location | Chloroplasts (in mesophyll cells of leaves) |
| Pigment | Chlorophyll (green; absorbs red and blue light best; reflects green) |
| Conditions needed | Light, chlorophyll, CO₂, water, suitable temperature |
| Plant Transport System | Structure | Function |
|---|---|---|
| Xylem | Hollow tubes; dead cells | Transports water and minerals from roots to leaves (unidirectional, upward) |
| Phloem | Living cells with sieve tubes and companion cells | Transports food (glucose/sucrose) from leaves to all plant parts (bidirectional) |
| Root hairs | Thin extensions of root cells | Increase surface area for water and mineral absorption |
| Stomata | Tiny pores in leaves controlled by guard cells | Gas exchange (CO₂ in, O₂ and water vapour out); transpiration |
PART 2 — Detailed Notes
Photosynthesis: The process by which green plants (and some bacteria) convert light energy into chemical energy (glucose), using carbon dioxide and water.
6CO₂ + 6H₂O → (light energy, chlorophyll) → C₆H₁₂O₆ + 6O₂
Two stages:
- Light reactions (Photo stage): Occur in thylakoid membranes; water is split (photolysis), releasing O₂; ATP and NADPH produced
- Calvin Cycle (Synthesis stage): Occur in stroma; CO₂ is fixed into glucose using ATP and NADPH
Chlorophyll: The green pigment that absorbs sunlight. Found in chloroplasts. Contains magnesium at its centre. Absorbs red and blue light; reflects green light (hence leaves appear green).
Stomata (singular: Stoma): Tiny pores on the surface of leaves, mainly on the underside. Surrounded by two guard cells that regulate opening and closing. Open during day for CO₂ intake and close at night. Also allow water vapour loss (transpiration).
Transpiration: Loss of water in the form of vapour from plant surfaces (mainly through stomata). Creates a pull (transpiration pull) that draws water up the xylem from roots. Contributes to local humidity and the water cycle.
Nitrogen Fixation: Plants need nitrogen (for proteins, DNA). Most cannot use atmospheric N₂ directly. Nitrogen-fixing bacteria (Rhizobium — in root nodules of legumes; Azotobacter, Cyanobacteria — free-living) convert N₂ into ammonia (NH₃), which plants can absorb. This is why legumes (pulses) are important for soil fertility and crop rotation.
Saprophytes: Plants that feed on dead and decaying organic matter. Example: mushrooms, bracket fungi, Monotropa. Unlike green plants, they have no chlorophyll.
Forests as Carbon Sinks — Climate Change
Forests store carbon in their biomass (wood, roots, leaves) and in soil. Global forests absorb approximately 2.6 billion tonnes of CO₂ per year (about 25% of annual human emissions).
India's Forest Cover:
- India's total forest and tree cover: 25.17% of geographic area (ISFR 2023)
- Target under National Forest Policy 1988: 33% geographic area under forest/tree cover
- India sequestered 2.29 billion tonnes of CO₂ equivalent through its forest and tree cover as of 2021 (BUR submission to UNFCCC)
- India's NDC 2.0 (2022): Create additional carbon sink of 2.5–3 billion tonnes of CO₂ equivalent through forests and tree cover by 2030
- India's NDC 3.0 (Cabinet approved March 25, 2026, covers 2031-2035): Carbon sink target raised to 3.5–4 billion tonnes CO₂-equivalent — requires continued large-scale afforestation and forest quality improvement
Green India Mission (GIM): One of the 8 missions under National Action Plan on Climate Change (NAPCC); aims to increase forest cover on 5 million ha and improve quality of forest cover on another 5 million ha by 2030.
Deforestation and Carbon Release:
- Deforestation converts forests from carbon sinks to carbon sources
- Amazon deforestation, South Asian forest fires, and Southeast Asian palm oil plantations are the largest sources of land-use change emissions globally
- REDD+ (Reducing Emissions from Deforestation and Forest Degradation) — UN mechanism to compensate developing countries for preserving forests
Nitrogen Cycle and Agriculture:
- Synthetic nitrogen fertilisers (urea, DAP) supply nitrogen to crops but cause problems: runoff leads to eutrophication; excess use causes soil acidification; production is energy-intensive (uses natural gas)
- Biofertilisers (Rhizobium, Azospirillum, PSB — Phosphate Solubilising Bacteria) promote natural nitrogen fixation — promoted under PM Pranam (Programme for Restoration, Awareness, Nourishment and Amelioration of Mother Earth)
- Pulse crops in crop rotation fix atmospheric nitrogen, reducing fertiliser requirement
Ecosystem Services from Plants — UPSC GS3 Mains
Plants provide essential ecosystem services that have economic value:
- Provisioning services: Food (crops, fruits), timber, fibre, medicinal plants, rubber, resins
- Regulating services: Carbon sequestration, oxygen production, water cycle regulation, flood control, soil stabilisation, pollination, pest control
- Cultural services: Aesthetic value, spiritual significance (sacred groves — devaravana in Karnataka, orans in Rajasthan)
- Supporting services: Nutrient cycling (nitrogen, phosphorus, carbon), habitat for biodiversity, primary production
Economic Valuation of Ecosystem Services: The TEEB (The Economics of Ecosystems and Biodiversity) framework and India's National Biodiversity Action Plan attempt to value these services. India's Compensatory Afforestation Fund Act (CAMPA), 2016 collects funds from industries diverting forest land and uses them for afforestation — recognising the economic value of forests.
Photosynthesis and Food Security: All food ultimately derives from photosynthesis. Net Primary Productivity (NPP) — the rate of photosynthetic production minus plant respiration — determines the maximum food available to all other organisms in an ecosystem. Threats to plant productivity (climate change, drought, soil degradation, air pollution with tropospheric ozone) threaten global food security.
CAM and C4 Plants — Adaptation to Stress:
- C3 plants (rice, wheat, soybeans — most crops): Standard photosynthesis; less efficient in hot, dry conditions
- C4 plants (maize, sugarcane, sorghum): More efficient in hot, sunny conditions; concentrate CO₂ around RuBisCO enzyme
- CAM plants (cacti, succulents, pineapple): Open stomata only at night to conserve water; store CO₂ for daytime photosynthesis Climate change may advantage C4 crops in warmer regions — relevant to crop adaptation strategies.
[Additional] 10a. India's Ethanol Blending Programme — Biofuel from Plants
The chapter covers photosynthesis (plants fix atmospheric CO2 into glucose/starch) and mentions biofertilisers (PM-PRANAM). What is missing is India's largest plant-biomass-to-fuel policy: the Ethanol Blended Petrol (EBP) Programme, where sugarcane, maize, and surplus rice are converted into ethanol and blended with petrol — replacing fossil fuel with solar-energy-captured-by-plants. India crossed 20% ethanol blending in 2025, five years ahead of the original 2030 target.
Ethanol Blending — The Photosynthesis Connection:
Photosynthesis: 6CO₂ + 6H₂O + sunlight → C₆H₁₂O₆ (glucose) + 6O₂
Fermentation (breaking glucose into ethanol): C₆H₁₂O₆ → 2C₂H₅OH (ethanol) + 2CO₂
The biofuel carbon cycle: Plants absorb CO₂ from air via photosynthesis → glucose is converted to ethanol via yeast fermentation → ethanol combusted in vehicle engines → CO₂ released back to air → absorbed again by next year's crops. This is why biofuels are considered "low-carbon" — the CO₂ they release was recently absorbed from the atmosphere, unlike fossil fuels that release carbon stored for millions of years.
| Term | Meaning |
|---|---|
| E20 | Petrol blended with 20% ethanol (and 80% conventional petrol) |
| ESY (Ethanol Supply Year) | November to October — India's ethanol blending calendar year |
| Feedstock | Raw material used to produce ethanol: sugarcane (juice, molasses), damaged/surplus food grain (maize, rice, wheat) |
| Compressed Biogas (CBG) | Methane-rich gas produced by anaerobic decomposition of agricultural waste, cattle dung, and organic matter — used as vehicle fuel |
| SATAT | Sustainable Alternative Towards Affordable Transportation — India's CBG scheme |
[Additional] India's Ethanol Blending Programme — Milestone Achievement and Policy Framework (GS3 — Energy / Agriculture / Environment):
Legal/policy framework:
- National Policy on Biofuels 2018 (amended 2022): Sets mandatory blending targets; originally set E20 by 2030; 2022 amendment advanced the E20 target to ESY 2025-26 (Ethanol Supply Year 2025-26)
- Allows multiple feedstocks: sugarcane juice, B-heavy molasses, C-heavy molasses, damaged/surplus food grain (maize, rice, wheat, sorghum), sweet sorghum, sugar beet
- Ministry: Ministry of Petroleum and Natural Gas; implementing: Oil Marketing Companies (OMCs — IOCL, BPCL, HPCL)
Blending trajectory — from 1.5% to 20% in a decade:
| Period | Ethanol Blending % |
|---|---|
| 2014 | 1.5% |
| June 2022 | 10% (achieved 5 months early) |
| ESY 2022-23 | 12.06% |
| ESY 2023-24 | 14.60% |
| ESY 2024-25 | ~19.17% (September 2025 data) |
| 2025 | 20% milestone crossed (Union Minister Hardeep Singh Puri announced — five years ahead of original 2030 target) |
Ethanol production scale-up:
- 2014: 38 crore litres produced
- June 2025: 661.1 crore litres produced — ~17× increase in 11 years
- ESY 2025-26 OMC allocation: ~1,048 crore litres
Feedstock shift — grain dominates:
- In ESY 2024-25, grain-based feedstocks contribute ~66-69% of total ethanol; maize alone accounts for 48-51% — making it India's No. 1 ethanol feedstock
- Sugarcane (molasses + juice): ~31-34%
- Government approved 5.2 million MT of FCI surplus rice for ethanol in ESY 2024-25
SATAT (Compressed Biogas):
- Launched: 1 October 2018 (Ministry of Petroleum and Natural Gas)
- Target: 5,000 CBG plants producing 15 MMT of CBG annually by 2030
- Progress (2024): 103 operational CBG plants (72 under SATAT); 174 plants under construction; 22,097 tonnes of CBG sold in FY 2023-24
- 5% CBG blending mandate by 2028 is the government's goal
- CBG connects to GOBARdhan (waste-to-wealth): cattle dung + agricultural waste → biogas + organic manure → double benefit
UPSC synthesis: Ethanol blending connects this chapter's photosynthesis (plants fixing solar energy into sugars) to India's energy security and carbon reduction policy. The biofuel carbon cycle is a near-closed carbon loop vs the open fossil fuel cycle — a key climate distinction. India's EBP achieves multiple policy goals simultaneously: reduces import bill (~Rs 1.36 lakh crore cumulative forex savings (as of 2025-26) in foreign exchange), cuts GHG emissions from transport, provides additional income to sugarcane farmers, and utilises surplus grain stocks. Key exam facts: E20 target advanced from 2030 to ESY 2025-26 by NPB 2022 amendment; 20% milestone crossed in 2025 (5 years ahead of original target); 661.1 crore litres produced by June 2025 (from 38 crore in 2014); maize is now India's top ethanol feedstock (48-51%); SATAT = 5,000 CBG plants target by 2030.
[Additional] 10b. India's Agroforestry Policy — Trees on Farms as Carbon Sinks
The chapter covers forests as carbon sinks (India's 2.29 billion tonnes CO2-eq carbon sink, NDC target 3.5-4 billion tonnes) and mentions the Green India Mission. What is missing is India's specific policy for putting trees ON agricultural land — agroforestry. India was the first country in the world to create a National Agroforestry Policy (2014). Agroforestry now covers 28.42 million hectares (~8.65% of India's land area) and contributes to India's NDC carbon sink target through photosynthesis-driven carbon storage in woody tree biomass.
Agroforestry — Definition and Types:
| Type | Description | Example |
|---|---|---|
| Agrisilviculture | Crops grown alongside trees | Wheat + eucalyptus rows in Punjab/Haryana |
| Silvopasture | Livestock grazing under or among trees | Cattle grazing under teak plantations |
| Agrosilvopastoral | Crops + trees + livestock | Mixed systems in NE India |
| Multipurpose tree systems | Trees that provide fodder, fruit, fuel, timber | Moringa + cereal crops |
| Homestead farming | Multiple species in household gardens | Kitchen gardens with multiple tree species |
Why trees on farms store more carbon than annual crops:
- Annual crops (wheat, rice, maize): Carbon absorbed during growing season is released back at harvest; net long-term storage is minimal
- Trees: Carbon fixed via photosynthesis is stored in woody biomass (trunk, branches, roots) for decades — providing long-term carbon sequestration
- ICAR-CAFRI estimates: Agroforestry systems sequester 0.25 to 76.55 Mg carbon per hectare per year depending on system; national average ~0.35 Mg C/ha/year
ICAR-CAFRI (Central Agroforestry Research Institute): Located at Jhansi, Uttar Pradesh. India's premier research institution for agroforestry. Has assessed carbon sequestration potential across 16 states and 15 agro-climatic zones. CAFRI Vision 2050 projects expanding agroforestry from 28.4 to 53 million hectares by 2050.
[Additional] India's National Agroforestry Policy 2014 and Sub-Mission on Agroforestry (GS3 — Agriculture / Environment / Climate):
National Agroforestry Policy 2014:
- India was the first country in the world to create a comprehensive National Agroforestry Policy (launched at World Agroforestry Congress, Delhi, February 2014)
- Key provisions: Simplified felling and transit regulations for trees on private farmland; online National Transit Pass System for inter-state timber transport; promoted credit and insurance for agroforestry practitioners; encouraged high-value species (teak, eucalyptus, poplar)
- Addresses 5Fs of rural demand: Food, Fuel, Fodder, Fertiliser, Fibre
Sub-Mission on Agroforestry (SMAF):
- Launched: 2016-17 under National Mission for Sustainable Agriculture (NMSA)
- Currently operational in 20 States and 2 UTs
- Financial support: Up to 50% of cost; funding pattern 60:40 (Centre:State) for most states; 90:10 for NE states, Himachal Pradesh, Uttarakhand; 100% Central for UTs
- Equity provisions: At least 50% of funds for small and marginal farmers; 30% beneficiaries must be women farmers
- Five components: Nursery development for quality planting material; peripheral/boundary plantation; low-density plantation on farmland; high-density block plantation; demonstration models with capacity building
India's agroforestry area and NDC contribution:
- Total agroforestry area: ~28.42 million hectares (~8.65% of total geographic area) — up from ~25.32 million hectares in 2013
- India's NDC (2022) target: Create additional carbon sink of 2.5-3 billion tonnes CO2-equivalent through forests and tree cover by 2030
- India's NDC 3.0 (2026): Raised to 3.5-4 billion tonnes by 2035
- Progress: India has already created 2.29 billion tonnes CO2-eq sink (2021 data, BUR submission to UNFCCC)
- Projection: India is on track to exceed the 3 billion tonne target, reaching ~3.57 billion tCO2-eq by 2030 (TERI/Outlook Business, 2025) — agroforestry's woody biomass growth is a key contributor
- Agroforestry is classified under "Trees Outside Forests" (TOF) — explicitly included in India's NDC implementation strategy alongside conventional forest afforestation
UPSC synthesis: Agroforestry is the missing bridge between Chapter 10's photosynthesis (plants absorbing CO2) and India's climate policy (NDC carbon sink target). Trees on farms are photosynthetic carbon capture machines — the same process the chapter teaches operates at scale to create India's carbon sink. India's policy framework — National Agroforestry Policy (2014, first in world) → Sub-Mission on Agroforestry (2016-17) → ICAR-CAFRI research (Jhansi) → 28.42 million hectares of agroforestry area — is a complete UPSC Mains answer framework for sustainable agriculture + climate action. Key exam facts: India was first country with National Agroforestry Policy (2014); SMAF operational in 20 states + 2 UTs; 28.42 million hectares agroforestry; ICAR-CAFRI at Jhansi; agroforestry contributes to NDC carbon sink via woody biomass sequestration.
Exam Strategy
- Photosynthesis equation: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂. Know the reactants, products, and conditions. Plants release O₂ as a by-product — common Prelims trap: "what gas is released by plants during photosynthesis" (during day: O₂; during both day and night: CO₂ from respiration).
- Xylem transports water and minerals (upward, unidirectional, from roots to leaves). Phloem transports food/sugar (bidirectional, from source to sink — leaves to roots or growing regions). Classic MCQ distinction.
- India's forest cover target is 33% (National Forest Policy 1988). Current coverage is ~25.17% (ISFR 2023). The gap is a key policy concern.
- Nitrogen-fixing bacteria: Rhizobium (symbiotic, in root nodules of legumes — peas, beans, lentils, groundnut); Azotobacter and Cyanobacteria (free-living in soil). This connects to biofertilisers and sustainable agriculture.
- REDD+ (Reducing Emissions from Deforestation and Forest Degradation) is the UN climate mechanism to compensate developing countries for conserving forests. India is a recipient country. Administered under UNFCCC.
- Green India Mission: One of 8 NAPCC missions. Target: add 5 million ha + improve quality of 5 million ha forest cover. Ministry of Environment, Forest and Climate Change.
Practice Questions
Q1. Consider the following statements about photosynthesis:
- Photosynthesis occurs only during daytime.
- Oxygen released during photosynthesis comes from the splitting of water molecules.
- Chlorophyll absorbs mainly yellow and green light for photosynthesis.
Which of the statements given above is/are correct?
(a) 1 only
(b) 1 and 2 only
(c) 2 and 3 only
(d) 1, 2 and 3
(b) 1 and 2 only
Q2. Rhizobium bacteria are associated with nitrogen fixation in:
(a) Root nodules of cereal crops like wheat and rice
(b) Root nodules of leguminous plants like peas and groundnut
(c) Stems of aquatic plants
(d) Leaves of tropical trees
(b) Root nodules of leguminous plants like peas and groundnut
Q3. Which of the following is/are correct about REDD+?
- It stands for Reducing Emissions from Deforestation and Forest Degradation.
- It is a mechanism under the UNFCCC to compensate developing countries for forest conservation.
- India does not participate in REDD+ as it is a developed economy.
Which of the statements given above is/are correct?
(a) 1 only
(b) 1 and 2 only
(c) 2 and 3 only
(d) 1, 2 and 3
(b) 1 and 2 only
