Uploaded by Ryan Li

4.2 Energy Flow

Sunlight and Ecosystems
- Initial source of energy
- Harvested through photosynthesis
- Done by producers
o Plants
o Eukaryotic algae
o Cyanobacteria
- Amount of energy harvested by and/or supplied to ecosystems varies
o E.g. Sahara has large energy supply, low energy harvest
o E.g. Redwood forests have low energy supply, high energy harvest
Energy Conversion
- Producers absorb light energy using chlorophyll
- Photosynthesis converts light energy into chemical energy:
o Carbohydrates
o Lipids
o Other carbon compounds
- Some of the carbon compounds are lost as heat energy but most remain in the plant
cells and are available to heterotrophs
Energy in Food Chains
- Chemical energy flows through food chains through feeding
- Most food chains have between 2-5 organisms
- Energy is lost as it moves up the food chain
Respiration and Energy Release
- Chemical energy in carbon compounds is not useable by the cell
- Cellular respiration converts this energy into a useable source ATP
- Energy transformation is not 100% efficient
o Some energy is lost as heat
Where does the heat go?
- All organisms lose heat via respiration
- Heat is completely lost into the environment and can’t be recycled
o Not that big of a problem because sunlight keeps coming in
- Only 10-20% of energy used typically from one tropic level to the next
- Goes from producers, primary consumer, secondary, tertiary, quaternary consumers
- How is energy lost?
o Not all parts of the organism are consumed. Parts are rejected and will decay.
o Not all parts consumed can be digested (e.g. hair and fur)
o Some organisms die of natural causes (not eaten therefore energy not passed)
o Heat loss via cellular respiration, energy loss for mechanical energy
(movement), energy loss for homeostasis (maintaining body temperature)
Energy Loss and Ecosystems
Biomass is the total mass of a group of organisms
It includes:
o Cells and tissue
o Carbohydrates and other carbon compounds
Because carbon compounds have energy, biomass has energy
A trend has been found…
o The amount of energy added to biomass by each successive trophic level is
o In other words, energy is lost
Drawing a Pyramid of Energy
Choose scale (1cm=10000kJm-2y-1)
Decide the height of each horizontal bar (2cm is usually good)
Calculate the length of each bar
Find the center of the page
Title and label the stages with a scale included