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📌 Key Points
- Ecosystem = biotic (living organisms) + abiotic (sunlight, water, soil, temperature, gases) factors in defined area
- Producers (plants): Create energy via photosynthesis. Primary consumers (herbivores): Eat plants. Secondary consumers (carnivores): Eat herbivores. Decomposers: Break down dead matter, return nutrients to soil
- Food chain: Linear sequence showing energy transfer (Plant → Herbivore → Carnivore). Food web: Multiple interconnected chains showing realistic complex feeding relationships
- 10% Law: Only ~10% of energy transfers between trophic levels; ~90% lost as heat through respiration, movement, digestion. Explains why fewer carnivores than herbivores
- Trophic level: Position in food chain. Level 1 = Producers (plants). Level 2 = Primary consumers. Level 3 = Secondary consumers. Usually 4-5 levels max due to energy limits
- Pyramid of numbers: Shows organism count at each level. Producer level most numerous. Can be inverted (few large trees, many small insects)
- Pyramid of biomass: Shows total organism mass at each level. Usually pyramid-shaped. Rarely inverted. Measured in grams/m²
- Pyramid of energy: Shows energy content at each level. ALWAYS pyramid-shaped (never inverts) because energy always decreases following 10% law
- Carbon cycle: Photosynthesis (plants absorb CO₂) → Respiration (release CO₂) → Decomposition (dead matter releases CO₂) → Combustion (fossil fuels release ancient CO₂)
- Nitrogen cycle: N₂ in atmosphere (unusable) → Nitrogen fixation (bacteria convert to NO₃⁻) → Assimilation (plants absorb, animals eat) → Decomposition (returns to soil) → Denitrification (converts back to N₂)
- Water cycle: Evaporation (sun heats water to vapor) → Transpiration (plants release water) → Condensation (vapor cools to liquid) → Precipitation (rain/snow) → Collection → Cycle repeats
- Biodiversity: Variety of species, genes, ecosystems. Genetic diversity = different genes in species. Species diversity = different organisms. Ecological diversity = different ecosystems
- Importance of biodiversity: Stability (resists changes), Productivity (efficient resource use), Human benefits (food, medicine), Ecosystem services (oxygen, water purification, pollination)
- Endangered species: Very few individuals remaining, at risk of extinction. Examples: Bengal tiger, Indian rhinoceros. Caused by habitat loss, poaching, pollution, climate change
- Deforestation: Removing forests for agriculture/logging. Effects: Habitat loss, soil erosion, increased CO₂, reduced biodiversity, floods
- Eutrophication: Excess nutrients (N, P) in water → algal blooms → oxygen depletion → dead zones. Fish die. Caused by agricultural runoff, sewage
- Climate change: Rising greenhouse gases (CO₂, CH₄) trap heat → global warming. Causes: Fossil fuel burning (70%), deforestation (18%), agriculture (12%). Effects: Temperature rise, melting ice, sea level rise, extreme weather
- Sustainable development: Meeting current needs without harming future generations. Strategies: renewable energy, 3Rs (reduce/reuse/recycle), sustainable agriculture, forest conservation, pollution control
- 3Rs: Reduce = use less resources. Reuse = extend product life. Recycle = process waste into new products. Decreases waste, pollution, resource extraction
- Conservation strategies: Protected areas (national parks), legal protection (poaching laws), breeding programs, habitat restoration, sustainable practices, education, international cooperation
📘 Important Definitions
⚠️ Common Mistakes
✗ Wrong: All organisms in an ecosystem are consumers.
✓ Correct: Ecosystems need producers (plants) creating energy and decomposers breaking down waste. Consumers alone cannot survive.
✗ Wrong: Food chain shows all feeding relationships in ecosystem.
✓ Correct: Food chain shows only one linear path. Food web shows multiple interconnected chains showing realistic complexity.
✗ Wrong: Energy at each trophic level increases due to accumulation.
✓ Correct: Energy decreases (10% rule). ~10% transfers to next level; ~90% lost as heat. This limits food chain length to 4-5 levels.
✗ Wrong: Decomposers are consumers eating dead organisms.
✓ Correct: Decomposers break down organic matter chemically, absorbing released nutrients. They're distinct group, not consumers.
✗ Wrong: All nutrient cycles move matter from biotic to abiotic only.
✓ Correct: Nutrient cycles are bidirectional: Abiotic (soil/air) ↔ Biotic (organisms) ↔ Abiotic. Matter cycles repeatedly.
✗ Wrong: Nitrogen gas (N₂) in atmosphere is directly usable by all organisms.
✓ Correct: N₂ is chemically inert, unusable. Must be fixed (converted to NO₃⁻) by lightning or bacteria before plant absorption.
📝 Exam Focus
These questions are frequently asked in CBSE exams:
Explain ecosystem structure with biotic and abiotic factors. Draw food chain and food web. Compare.
5m
Derive pyramid of numbers, biomass, energy. Explain why energy pyramid always pyramid-shaped.
5m
Explain carbon cycle and nitrogen cycle with diagrams. How do humans affect each cycle?
5m
What is biodiversity? Why is it important? Describe threats and conservation strategies.
5m
Explain environmental issues (pollution, deforestation, climate change). What are sustainable solutions?
5m
Define trophic level and 10% law. Calculate energy transferred through food chain given starting value.
3m
What is eutrophication? What causes it and what are its effects on aquatic ecosystems?
3m
Explain relationship between sustainable development and protecting biodiversity.
3m
🎯 Last-Minute Recall
Close your eyes and try to recall: Key definitions, formulas, and 3 common mistakes. If you can recall 80% without looking, you're exam-ready!