Environmental Science / Unit 2: Ecosystems and Energy Flow
2.2 Energy Flow, Food Chains and Food Webs
Notes
Nearly all ecosystems run on energy from the sun, captured by producers through photosynthesis.
- Producers (autotrophs) make their own food. Consumers (heterotrophs) eat other organisms: herbivores, carnivores, omnivores. Decomposers (bacteria and fungi) break down dead matter and return nutrients to the soil.
- A food chain shows one path of energy: grass, grasshopper, frog, snake, hawk.
- A food web shows many linked food chains and is more realistic.
- Energy flows in one direction and is lost as heat; matter is recycled.
- Photosynthesis: $6CO_2 + 6H_2O + \text{light} \rightarrow C_6H_{12}O_6 + 6O_2$. Cellular respiration releases the energy again.
- Chemosynthesis lets some bacteria at deep-sea vents make food from chemicals instead of sunlight.
Practice
In a food chain of grass, grasshopper, frog, and snake, the frog is a:
The grasshopper eats producers (primary); the frog eats the grasshopper (secondary).
What is the main role of decomposers?
Decomposers recycle nutrients from dead organisms.
Which statement about energy and matter in ecosystems is correct?
Nutrients cycle; usable energy must keep arriving from the sun.
Ready for more? Take the Unit 2 test.