Energy Flows in Ecosystems
AP Env Sci 2011-2012
Why Green?
• Reminder: Photosynthesis “sets the table” for all energy
flows that follow:
• Converts Low Potential Energy compounds to High
Potential Energy compounds
Photosynthesis – Fate of Glucose
Photosynthesis
6 CO2 + 6 H20
C6H12O6 + 6 O2
Respiration
C6H12O6 + 6 O2
Where’s the energy?
6 CO2 + 6 H20
Photosynthesis – Fate of Glucose
• Not much value if all glucose is used for energy
• Where does the glucose go?
– Making other organic molecules in plant
– Broken down to release energy for plant activities
– Storage as starch or oils
• Plants make new organic matter – primary
producers.
Net Primary Productivity (NPP)
• Primary Productivity:
– Gross Primary Productivity: total amount of
photosynthetic activity
– Net Primary Productivity: gross primary
productivity minus energy the plants themselves
consume. NPP is rate at which new organic matter is
made available to consumers in ecosystem.
– NPP Lab Coming Up!
Consumers and Cell Respiration
• Consumers break down complex organic compounds
(from producers) into simpler compounds (ie. Glucose)
• Cells get energy from respiration –
– High potential energy glucose to low potential energy
CO2.
– Reaction releases energy:
C6H12O6 + 6 O2
6 CO2 + 6 H20 + energy
Respiration
• Note that Oxygen is released in photosynthesis but
used in respiration.
– Respiration is an oxidation reaction
• Conversion of chemical potential energy (glucose) to
energy for the body is not 100% efficient
– Result is body heat
The Fate of Food
• Of the food absorbed: 60-90% oxidized for energy
• Of the food absorbed: 10-40% converted to body tissue
• Production of body tissue: Secondary Production
Focus on Detritus Feeders and
Decomposers
• Detritus is largely cellulose (“fiber”)
– We cannot digest this, but other organisms can
• Most decomposers use O2 for cell respiration (like us)
– Cellulose broken down into CO2, etc.
– Fermentation: alternative where oxygen is limited
Fermentation
• Certain bacteria and yeast
• Chemical breakdown of glucose in absence of
oxygen– products include ethyl alcohol, methane, acetic acid
• Happens in anaerobic environments
– Industrial fermentation
– Lake sediment
– Marshes, swamps
– Animal gut
– landfills
Cycle vs Flow
• Flow of Energy – starts with the Sun
• Cycling of Nutrients – producer, consumer,
decomposer