Ecosystems & Energy Flow

Ecosystem & Energy Flow

In an ecosystem, energy flows one way from the sun through producers to consumers, and most is lost as heat at each step. Matter cycles, but energy does not. Only about 10% moves to the next trophic level, so the energy pyramid narrows upward. Slide the transfer efficiency and watch how energy shrinks on the pyramid.

Energy flows in one direction

☀️ Sun → producer → consumer → ...

①Sun → producer (photosynthesis) → primary → secondary consumer → ...

②Most energy is lost as heat at each level

③Matter cycles, but energy does not!

Energy Pyramid

Energy transfer efficiency (%)10%

💡 Try changing efficiency

①Default 10% — the famous "10% rule"

②Even with higher efficiency, top-level energy drops sharply

③By tertiary consumer, only 0.1% of original energy remains!

Ecosystem Components

Components of an Ecosystem

Ecosystem Interactions

Population Interactions

ChartInterspecies Interactions

Type	Species A	Species B	Example
Competition	harm (-)	harm (-)	shared food competition
Predation	benefit (+)	harm (-)	lion-antelope
Parasitism	benefit (+)	harm (-)	parasite-host
Mutualism	benefit (+)	benefit (+)	bee-flower, termite-protozoa
Commensalism	benefit (+)	neutral (0)	shark-remora

Worked Examples

Example 1

A producer holds 10000 kcal and the energy transfer efficiency is 10%. How much energy does the secondary consumer receive?

Only 10% of energy passes to the next level each step (the 10% rule).

Producer 10000 → primary consumer 1000 → secondary consumer 100 kcal.

▸ 100 kcal

10% rule: ×0.1 per step. Two steps up is ×0.01, so 1% of 10000 = 100 kcal.

Example 2

A bee gets nectar from a flower while pollinating it. What interspecific interaction is this, and the benefit/harm to each?

If both species benefit (+, +), it is mutualism.

The bee gains food (nectar) and the flower gains pollination (reproduction), so both benefit → mutualism.

▸ Mutualism (bee +, flower +)

Interactions are classified by the benefit(+)/harm(-)/neutral(0) combo. (+,+)=mutualism, (+,-)=predation/parasitism, (+,0)=commensalism.

Summary

10% Rule of Energy Flow

upper trophic energy ≈ 10% of below

most energy lost as respiration (heat) at each level

Matter Cycle vs Energy Flow

matter: cycles (producer↔consumer↔decomposer) / energy: one-way (sun→heat)

matter is recycled, energy is not

CSAT-style

Which statement about energy flow and matter cycling in an ecosystem is INCORRECT?

①Energy starts at the Sun and flows in one direction

②Energy decreases at higher trophic levels

③Matter such as carbon and nitrogen cycles in the ecosystem

④Energy cycles within the ecosystem like matter

⑤Most energy at each level is lost as heat through respiration

▸ ④ Energy cycles within the ecosystem like matter

Matter (carbon, nitrogen) cycles, but energy flows one way: Sun → heat.

Energy does not cycle, so ④ is incorrect.

🎯 Exam Points

①Energy: sun → producer → consumer → heat (one-way)

②10% rule: about 10% transferred up, rest lost as respiration

③Pyramids: energy, biomass, numbers

④Matter cycles (C, N), energy doesn't

⑤Stability: more complex food web → more stable

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