4.2 ENERGY FLOW

Photoautotrophs

Use pigments such as chlorophyll to trap light energy which is converted into chemical energy in carbon compounds

Chemoautotrophs

Use energy from chemical processes 

Example: Volcanic vents

All Autotrophs convert Carbon Dioxide [from atmosphere or dissolved in water] into Organic Compounds

The light energy is transferred into bonds between the atoms of a carb molecule [chemical energy] 

Consumers ingests organic matter which is living or recently killed 

Food Chains: Show the flow of energy through the trophic levels of a feeding relationship 

Trophic Level: Feeding position of an organism in a food chain

Food Chains mostly only have 3 to 4 trophic levels because of Theories of energy flow and energy losses

Only a small proportion of energy and biomass is passed on from one trophic level to another [10%]

The amount of energy drops along Food Chains - 4th and 5th Trophic Levels too little energy remains to sustain another level

Pyramids of Energy: A diagram that shows the flow of energy between trophic levels in a community

Measured in units of energy, per unit area per unit time KJ m-2 y-1

90% of energy is lost between Trophic Levels:

• Not ingested
• Not digested
• Excreted
• Lost as heat from Respiration

As the Trophic Level increases the biomass and energy available decreases 

Energy losses between Trophic Levels limit the length of Food Chains

As energy is lost between Trophic Levels Biomass is lost too [each level smaller than one below]

Biomass is used to indirectly measure energy transfers 

• Cell Respiration

Organisms release energy from carbon molecules to be used for muscle contration or active transport

Energy which is converted into heat energy is lost 

Heat energy cannot be converted back into chemical energy which is why 

Heat is lost from the ecosystem

An energy source is required to replace the energy lost [sunlight]

• Food passed to Saprotrophs rather than the next Trophic Level 

Organisms die before eaten [disease]

Parts of organisms cannot be eaten [hair, bones]

Indigestible parts [cellulose]

Energy stored in organic molecules can be transferred by cell respiration to ATP

ATP is used by cells to support their metabolism:

• Building and breaking molecules
• Homeostasis
• Growth

Heat energy is also produced but is wasted 

Ineffiencies in Energy Transfer 

Toxic organic molecules are excreted

Ingested material is not absorbed and is egested 

Parts of an organism remain uneaten [fibres from plants and bones from animals]

Heat cannot be converted back into chemical energy so it is lost from the ecosystem

Solution: Energy source to replace the lost energy - Sunlight

Thermal energy released from the organism dissipates and is eventually lost from the ecosystem

Contrary to light and chemical energy heat energy cannot be converted into forms that is useful for the organism

Ecosystems require a continuous source of light to survive 

Useful energy transfers from chemical energy for the organism 

• Kinetic Energy - Muscle Contractions
• Electrical Energy - Nerve Impulses
• Light Energy - Bioluminscense 
• Chemical Energy - Anabolism
• Heat Energy - Body Temperature in Endotherms