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 O26 CO2 + 6 H20

Where’s the energy?

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:

6 CO2 + 6 H20 + energyC6H12O6 + 6 O2

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