Energy Dynamics
How can we measure energy flow?
• Indirectly with biomass
• Where does the energy captured go?
– Reproduction
– Cellular respiration
– Synthesis
– locomotion
– Decomposers
– Unavailable or Undigested food
– Lost as heat
Recycling
• Is energy recycled in an ecosystem?
• Are materials recycled?
• Which materials are recycled?
Model for energy capture by plants
How can we measure the
biomass and energy of a living plant?
• Calculate the percentage of dry to wet mass
• Each gram of plant biomass represents about
4.35 kcal/gram
• Compare the biomass of plants sampled at 7 days
and later at 14 days by graphing the results.
Plant Productivity
• Gross productivity
– A measure of total energy captured by a plant
• Net productivity
– The net amount of energy captured and stored by
producers in an ecosystem
• Primary productivity is a rate:
– Energy captured by photosynthetic organisms in a
given area per unit of time
Second Law of Thermodynamics
• When energy is converted from one form to
another, some energy will be lost as heat.
Light energy → chemical energy → consumers
↓
↓
heat
heat
Primary Productivity
∆ biomass
unit of time
Complicating Factors
• Living organisms have a large percentage of
water in addition to the organic compounds of
biomass.
• Organisms must be dried out.
• This can’t be done multiple times on a living
organism.
• Different organic compounds have different
amounts of energy.
• Proteins and carbohydrates have different
amounts of energy but usually:
– about 4 kcal/gram dry weight
• Fats
– About 9 kcal/gram dry weight
Model Organisms
Flower:
Brassica rapa
(Wisconsin
Fast Plants)
Calculating Net Primary Productivity
• After determining the dry mass after a 7-day
period of growth, calculate
Total energy
7 days
14 plants = Net Primary Productivity
Cabbage White Butterflies: Pieris rapae
Calculating Energy Flow from Brussel
Sprouts to Cabbage White Butterfly Larvae
↗ respiration
Brussel sprouts → Butterfly larvae (biomass)
↘ frass (waste)
Data Tables and Graphs
• Collect all data in data tables and summarize
in words in your lab report.
• Graph the net primary productivity of the
plants at day 7 and day 14.
• Graph the energy transfer (kcal) from brussel
sprouts to butterfly larvae over three days of
feeding.