Energy in the Biosphere: A Closed System
Introduction
- Earth is considered a closed system: minimal exchange with outer space.
- Few exceptions: asteroids entering, spaceships leaving.
- Earth's system does not receive new matter.
Laws of Thermodynamics
- First Law: Energy is not created or destroyed, only transformed.
- Types of energy: kinetic, potential, chemical, thermal, etc.
- Second Law: No energy conversion is 100% efficient.
- Most energy loss occurs as heat.
Energy Transfer in Ecosystems
- Energy loss through food chains.
- Rule of thumb: only 10% of energy is passed to the next trophic level.
- Example: 100 joules in plants > 10 joules in deer > 1 joule in wolf > 0.1 joules in hawk.
Trophic Levels
- Each trophic level represents a step in energy and matter transfer.
- Producers: First trophic level (e.g., plants).
- Primary Consumers: Second trophic level (herbivores).
- Secondary/Tertiary Consumers: Carnivores follow.
Food Chains and Food Webs
- Food Chain: Linear pathway of energy movement in an ecosystem.
- Example: Sun > Grass > Grasshopper > Gopher > Hawk.
- Food Web: Network of interconnected food chains.
- More complex interactions and dependencies.
- Example: Sun > Grass > Various herbivores > Different carnivores > Hawk.
Impact of Removing Organisms
- Removing prairie grasses affects multiple species dependent on them.
- Removing top predators (like hawks) impacts population dynamics of prey.
Limitations on Trophic Levels
- Most food chains have few trophic levels due to the rule of 10% energy transfer.
- Aquatic ecosystems may have more levels due to smaller consumer sizes.
- Example: Algae > Phytoplankton > Zooplankton > Minnows > Larger fish > Seals/Whales.
- Terrestrial ecosystems typically have 4-5 levels.
Energy Use
- Remaining energy used for: heat, movement, waste production, survival activities.
Conclusion
- Energy transfer is crucial in shaping ecosystem dynamics.
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