Lecture Notes: Energy Transfer in Ecosystems (C 4.2 Part 1)

Introduction

• Focus: Transfer of energy and matter, primarily energy transfers.
• Ecosystems: Composed of organisms, communities, and abiotic factors (e.g., air, water, soil).
• Systems: Can be open (resources/energy enter and exit) or closed.
• Most ecosystems are open systems.

Energy in Ecosystems

• Primary Energy Source: Sunlight, used in photosynthesis by producers (plants, algae, cyanobacteria).
• Variability: Amount of energy varies globally due to sunlight and abiotic conditions.
  • Example: Sahara Desert vs. Redwood Forest.
• Aquatic Systems: Light penetration varies; deeper waters rely on sources other than sunlight.

Closed Systems

• Rare ecosystems can be closed or restricted.
  • Example: Caves with no sunlight rely on chemosynthesis by bacteria.

Energy Transfer

• Food Chain: Linear sequence of energy transfer between organisms (producers to consumers).
• Apex Predator: Last organism in a food chain, not preyed upon.
• Food Web: Complex interactions in an ecosystem, multiple food chains.
  • Trophic Levels: Position of organism based on feeding relationships.

Role of Decomposers

• Decomposers: Consume dead/waste material, recycle energy.
  • Detritivores: Consume dead organic matter (e.g., insects, earthworms).
  • Saprotrophs: Perform external digestion, absorb nutrients (e.g., fungi, bacteria).

Autotrophs vs. Heterotrophs

• Autotrophs: Produce energy from inorganic substances, require external energy (sun, chemicals).
  • Photoautotrophs: Use sunlight (e.g., plants, algae).
  • Chemoautotrophs: Use chemical reactions (e.g., bacteria in deep sea vents).
• Heterotrophs: Obtain energy by consuming other organisms.
  • Digestive Process: Involves digestion, assimilation, and synthesis.

Cellular Respiration & ATP

• Both autotrophs and heterotrophs produce ATP via cellular respiration.
• ATP uses: Synthesizing molecules, transport, movement, temperature regulation.

Energy Pyramids

• Energy Pyramid: Depicts energy available at each trophic level.
  • Measured in kJ per meter squared per year.
  • Shows decreasing energy with each level due to inefficiencies.
  • Common inefficiencies: Incomplete consumption, digestion, and cellular respiration.

Inefficiencies in Energy Transfer

• Only ~10% of energy is transferred between trophic levels, 90% is lost.
• Energy losses limit biomass and trophic levels.
• Heat loss through cellular processes (e.g., muscle contraction).

Conclusion

• Energy in ecosystems flows from sunlight to heat, with inefficiencies limiting trophic levels.
• Next video will focus on matter transfer, particularly carbon.