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An ecosystem is a community of living organisms interacting with the nonliving parts of their environment, such as sunlight, water, air, and soil. Energy enters most ecosystems as sunlight and is captured by producers like plants and algae. That energy moves through food webs as organisms eat and are eaten. Matter is different because atoms are reused again and again within the ecosystem.
Key Facts
- Producers convert light energy into chemical energy by photosynthesis: 6CO2 + 6H2O + light -> C6H12O6 + 6O2.
- Cellular respiration releases energy from food: C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy.
- Energy flows one way through ecosystems and is eventually lost as heat.
- Matter cycles through organisms, soil, water, and air because atoms are conserved.
- Only about 10% of energy is usually transferred from one trophic level to the next.
- Biomass generally decreases at higher trophic levels because less energy is available.
Vocabulary
- Ecosystem
- An ecosystem is all the living organisms in an area plus the nonliving environment they interact with.
- Producer
- A producer is an organism, such as a plant or algae, that makes its own food using energy from sunlight or chemicals.
- Consumer
- A consumer is an organism that gets energy by eating other organisms or organic matter.
- Decomposer
- A decomposer is an organism, such as a fungus or bacterium, that breaks down dead matter and returns nutrients to the environment.
- Trophic level
- A trophic level is a feeding position in a food chain or food web, such as producer, primary consumer, or secondary consumer.
Common Mistakes to Avoid
- Saying energy cycles through an ecosystem is wrong because energy flows in one direction and is eventually released as heat.
- Forgetting decomposers is wrong because decomposers recycle nutrients from dead organisms and waste back into soil, water, and air.
- Assuming all energy from one trophic level moves to the next is wrong because most energy is used for life processes or lost as heat.
- Confusing food chains with food webs is wrong because a food chain shows one path of energy transfer, while a food web shows many connected feeding relationships.
Practice Questions
- 1 A meadow producer level contains 50,000 kJ of energy. Using the 10% rule, how much energy is available to primary consumers, secondary consumers, and tertiary consumers?
- 2 A pond contains 800 kg of producer biomass. If primary consumers have 12% of the producer biomass and secondary consumers have 15% of the primary consumer biomass, what is the biomass of each consumer level?
- 3 Explain why removing decomposers from a forest ecosystem would affect both plant growth and the flow of matter through the community.