Energy Flow in Ecosystems (HL IB ESS OLD COURSE - IGNORE)
Revision Note
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
Energy Flow in Ecosystems
Ecosystems rely on a constant supply of energy and matter to maintain their structure and function
Energy is essential for driving biological processes, while matter cycles through the ecosystem, being reused and recycled
Ecosystems are considered open systems, meaning they exchange both energy and matter with their surroundings
Energy enters ecosystems primarily from the sun, entering as sunlight and being converted into chemical energy by producers through photosynthesis
This energy is then transferred between trophic levels as organisms consume one another, with some energy lost as heat at each transfer
Decomposers break down organic matter, releasing energy and returning nutrients to the environment
Matter, such as nutrients and water, flows into and out of ecosystems through various processes like decomposition, nutrient cycling and precipitation
The first law of thermodynamics
Energy exists in many different forms, including light energy, heat energy, chemical energy, electrical energy and kinetic energy
The way in which energy behaves within systems can be explained by the laws of thermodynamics
There are two laws of thermodynamics
The first law of thermodynamics is as follows:
Energy can neither be created nor destroyed, it can only be transformed from one form to another
This is also known as the principle of conservation of energy
It means that the energy entering a system equals the energy leaving it
It means that as energy flows through ecosystems, it can only change from one form to another
The transfer of energy in food chains within ecosystems demonstrates the principle of conservation of energy:
Energy enters the system (the food chain or food web) in the form of sunlight
Producers convert this light energy into biomass (stored chemical energy) via photosynthesis
This chemical energy is passed along the food chain, via consumers, as biomass
All energy ultimately leaves the food chain, food web or ecosystem as heat energy
The second law of thermodynamics
The second law of thermodynamics states that:
Energy transfers in ecosystems are inefficient
This is because energy transfers in any system are never 100% efficient
The second law of thermodynamics explains the decrease in available energy within ecosystems:
In a food chain, energy is transformed from a more concentrated (ordered) form (e.g. light energy from the Sun), into a more dispersed or disordered form (heat energy lost by organisms)
Initially, light energy from the Sun is absorbed by producers
However, even at this initial stage, energy absorption and transfer by producers is inefficient
This is due to reflection, transmission (light passing through leaves) and inefficient energy transfer during photosynthesis
The energy that is converted to plant biomass is then inefficiently transferred along the food chain due to respiration and the production of waste heat energy
In ecosystems, the biggest losses occur during cellular respiration
When energy is transformed, some must be degraded into a less useful form, such as heat
As a result of these inefficient energy transfers, food chains are often short (they rarely contain more than five trophic levels)
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