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Ecology & Biodiversity
Ecosystems & Energy Flow
Trophic levels, the 10 % rule and ecological pyramids — how energy and matter move through ecosystems.
PART 1
Topic Breakdown & Traps
The Engineering Principle
Energy enters an ecosystem through primary producers and flows one-way through trophic levels (producer → herbivore → carnivore). By Lindeman's 10 % law, only about one-tenth of the energy at one level is passed to the next; the rest is lost as respiration heat. This limits food chains to a few links and makes the pyramid of energy always upright.
The Core Formula Matrix
Ten-percent law: energy to next level of the present level.
Trophic levels: T1 producers → T2 primary consumers → T3 secondary consumers → …
Gross vs net primary productivity: .
Pyramid of energy is always upright; pyramids of number/biomass can invert.
Trophic levels: T1 producers → T2 primary consumers → T3 secondary consumers → …
Gross vs net primary productivity: .
Pyramid of energy is always upright; pyramids of number/biomass can invert.
The ‘IIT Traps’
- ⚠Energy flow is one-way; only nutrients cycle.
- ⚠The energy pyramid is never inverted, unlike number/biomass pyramids.
- ⚠NPP = GPP − respiration, the energy actually available to consumers.
📚 Standard references
- Fundamentals of Ecology — Eugene P. Odum
- Ecology and Environment — P.D. Sharma
PART 2
Progressive 3-Tier Question Suite
Q1MEDIUM2 Marks · NAT
If primary producers fix 10,000 kJ/m² of energy, the energy available to secondary consumers (third trophic level) under the 10 % law is _____ kJ/m².
Q2BASIC1 Mark · MCQ
Net primary productivity (NPP) equals:
Q3HARD1 Mark · MCQ
Which ecological pyramid is always upright?