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.