Pyramids of Energy | Biology for GCSE/IGCSE - Year 11 PDF Download

Energy Flow in Ecosystems

• In ecosystems, energy flow is a crucial process that sustains life. Let's delve into the key concepts:
• Energy Consumption and Transfer: In order for energy to move through an ecosystem, it must be consumed. However, not all the energy an organism receives is passed on. For instance, when a vole consumes grass, only a portion of the energy is retained in new cells.
• Energy Loss in Trophic Levels: Energy is lost as it moves through trophic levels due to various factors:
  • Waste Production: Organisms produce waste products like urine, which removes energy from the system.
  • Heat Generation: Mammals and birds release energy as heat, especially those maintaining a constant body temperature.
  • Undigested Waste: Undigested waste, such as faeces, provides food for decomposers but represents lost energy from the ecosystem.
  • Energy Efficiency and Food Chains: The inefficiency of energy transfer explains why food chains are limited in length. Energy loss at each trophic level restricts the number of organisms in a chain. For instance, predators consuming barn owls would need to consume many to meet their energy needs due to the low energy transfer efficiency.

Energy Loss in Food Chains

• Energy Inefficiency: Energy loss occurs at each trophic level, limiting food chains to about 5 organisms due to inefficiencies.
• Energy Transfer Example: When an organism preys on another, like a barn owl, it only gains a small fraction (0.1J) of energy from each owl consumed.
• Survival Challenges: To survive, the predator must consume a large number of owls daily and expend minimal energy in hunting.
  • Requirement for Survival: The predator needs to consume numerous owls daily to meet its energy needs.
  • Energy Efficiency in Hunting: The predator must conserve energy during the hunting process to sustain itself.

A typical pyramid of energy would look like this:

Impact of Human Food Choices

• Humans are omnivores, obtaining energy from both plants and animals, allowing a choice in diet.
• These dietary choices influence agriculture and ecosystem usage.
• Consider different food chains involving humans:
  • Wheat → Cow → Human
  • Wheat → Human
• Considering energy transfer in food chains, it becomes evident that consuming wheat directly provides humans with more available energy compared to consuming cows that feed on wheat. 
• This is due to the energy loss as it moves up the trophic levels, resulting in less energy available for humans if they consume cows. 
• Thus, within a crop food chain, it is more energy efficient for humans to act as herbivores rather than carnivores. 
• In practice, humans often feed animals with plants that are unsuitable for human consumption, such as grass, or are too widespread for direct collection, like algae in the ocean, which indirectly contribute to the food chain.