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 ↓ ↓ heatheat

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 days14 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.