Ecosystem Class 12 Notes PDF Download | NCERT Chapter 12 NEET 2027

*Hello Friends 👋

Aaj apni baat karenge Class 12 Biology ke sabse scoring chapter ki - Ecosystem NCERT Chapter 12.

NEET 2027 me is chapter se 2-3 questions pakke aate hain. Maine aapke liye One Shot Notes + PDF ready kar di hai. Bilkul free me download kar lo.

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### *1. Ecosystem – Structure & Function*  

- *Ecosystem*: Term by A.G. Tansley. Structural & functional unit of nature.  

- *Types*: Terrestrial = Forest, Grassland, Desert. Aquatic = Pond, Lake, Ocean.  

- *Components*:  

    1. *Biotic*: Producers, Consumers, Decomposers.  

    2. *Abiotic*: Temperature, Light, Water, Soil, Inorganic nutrients.  

- *Functions*: Productivity, Decomposition, Energy flow, Nutrient cycling.  

### *2. Productivity*  

- *Primary Production*: Amount of biomass/organic matter produced by producers per unit area per unit time.  

- *GPP*: Gross Primary Productivity = Total organic matter via photosynthesis.  

- *NPP*: Net Primary Productivity = GPP - R. Available for consumers.  

  $$NPP = GPP - R$$  where R = Respiration losses.  

- *Secondary Productivity*: Rate of formation of new organic matter by consumers.  

- *NEET Gold*: Tropical rainforest = highest NPP. Open ocean = lowest NPP per unit area but total highest due to size.  

### *3. Decomposition*  

_Breakdown of complex organic matter by decomposers into inorganic raw materials._

**Step** **Process** **Details**

**1. Fragmentation** Detritivores break detritus into smaller pieces Earthworm = Detritivore

**2. Leaching** Water-soluble nutrients go into soil Percolation

**3. Catabolism** Enzymes from bacteria/fungi degrade detritus Releases inorganic nutrients

**4. Humification** Formation of dark amorphous humus Highly resistant, reservoir of nutrients

**5. Mineralisation** Humus degraded to release inorganic nutrients CO₂, H₂O, minerals

*Factors affecting Decomposition*:  

1. *Fast if*: Warm + Moist, Detritus rich in Nitrogen & Sugars.  

2. *Slow if*: Cold, Anaerobic, Detritus rich in Lignin & Chitin.  

### *4. Energy Flow*  

- *Unidirectional*: Sun → Producers → Consumers. Not recycled.  

- *10% Law*: Lindeman. Only 10% energy transferred from one trophic level to next. 90% lost as heat.  

- *Food Chain*: Grazing = Starts with producers. Detritus = Starts with dead organic matter.  

- *Food Web*: Network of food chains. More stable than food chain.  

- *NEET Trap*: GFC = Grazing Food Chain. DFC = Detritus Food Chain. DFC is major conduit of energy in terrestrial ecosystem.  

### *5. Ecological Pyramids*

**Pyramid** **Upright Example** **Inverted Example** **Always Upright?**

**Number** Grassland Tree ecosystem No

**Biomass** Grassland, Forest Sea - Phytoplankton biomass less than zooplankton No

**Energy** All ecosystems None Yes

*NEET Gold*: Pyramid of Energy is always upright because energy flow is unidirectional & 10% law.  

### *6. Ecological Succession*  

_Gradual, predictable change in species composition of an area._  

1. *Primary Succession*: Starts where no living organisms ever existed. Bare rock, new pond. Very slow.  

   Ex: Xerarch = on bare rock. Hydrarch = in water.  

2. *Secondary Succession*: Starts in area that lost all life due to fire, flood. Faster due to soil presence.  

*Xerarch Succession on Bare Rock*:  

Lichens = Pioneer → Bryophytes → Herbs → Shrubs → Trees = Climax community = Forest.  

*Hydrarch Succession in Water*:  

Phytoplankton → Submerged plant → Submerged free floating → Reed-swamp → Marsh-meadow → Scrub → Forest.  

*NEET Point*: Climax community = Stable, self-perpetuating, in equilibrium with environment.  

### *7. Nutrient Cycling / Biogeochemical Cycles*  

1. *Carbon Cycle*:  

      - *Reservoir*: Atmosphere = 71% CO₂. Oceans = 4x atmosphere. Fossil fuel.  

      - *Cycling*: Photosynthesis → Food chain → Respiration → Decomposition → Combustion.  

      - *Human Impact*: Burning fossil fuel ↑ CO₂ → Greenhouse effect.  

2. *Phosphorus Cycle*:  

      - *No respiratory release*. No gaseous phase.  

      - *Reservoir*: Rocks. Weathering → Soil → Plants → Animals → Decomposers.  

      - *NEET Gold*: Gaseous cycle = Carbon, Nitrogen. Sedimentary cycle = Phosphorus, Sulphur.  

### *8. Ecosystem Services*  

_Products of ecosystem processes_. Term by Robert Constanza.  

1. *Healthy Forest*: Purify air, Mitigate floods, Cycle nutrients, Generate fertile soil.  

2. *Value*: Services worth trillions of dollars per year.  

3. *Oxygen*: 50% from Amazon rainforest.  

### *9. Last 5 Year PYQ One Liners* `Ratta Maar Le`  

1. *Parthenium* = Carrot grass, came to India as contaminant. Caused pollen allergy.  

2. *Inverted Pyramid of Biomass* = Sea ecosystem. Zooplankton > Phytoplankton.  

3. *Pioneer Species*: Lichens on rock, Phytoplankton in water.  

4. *Humification* → Leads to accumulation of humus = dark amorphous substance.  

5. *10% Law* = Only 10% energy available for next trophic level = NEET 2021, 2023.  

6. *Standing Crop* = Mass of living material at a trophic level at a particular time.  

7. *DFC* = Detritus Food Chain = Major channel in terrestrial ecosystem.  

Diagram for NEET : Ecological pyramid Carbon cycle, Hydrarch & Xerarch succession