Energy budget lab: from plant to caterpillar
BiologyEcology & EnvironmentAges 17–18Virtual lab
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Next in Ecology & Environment
A virtual lab after AP Biology Investigation 10: weigh brussels sprouts and cabbage white caterpillars before and after feeding, dry samples to find dry mass, collect frass, convert biomass to kilocalories, then work out energy eaten, assimilated, lost in frass and lost to respiration, and production efficiency, and compare them with the 10% rule.
Lesson: Energy flow in ecosystems, ecological efficiency
What it shows
Not all the energy in food becomes animal. Some leaves as frass, and most of what is assimilated is spent on respiration, so only the rest becomes new biomass. This lab audits that energy as in the AP Biology Investigation 10 manual: dry masses of sprout, larvae and frass become kilocalories through the manual's energy values, while respiration is not measured but found as what is left over. Each trial has sample scatter, and respiration collects the errors of every weighing.
How to use
On the Feeding trial tab, set Larvae, Brussels sprout, Temperature and Days, then press Weigh and start, Feed the larvae, Weigh at the end, and Dry and weigh in turn. On the Energy budget tab, use the table of masses to work out the budget yourself and type it into the tasks. Press Work out and record to see the graphs. Switch Larva dry share between Measured from spare larvae and Assume 40% to compare.
Parameters you can change
- Screen Feeding trial, Energy budget
- Number of larvae 5–20
- Mass of brussels sprout 10–60 g
- Temperature 15–30 °C
- Days of feeding 1–5
- Larva dry share Measured from spare larvae, Assume 40%
Questions to explore
- With 10 larvae, a 30 g sprout, 25 °C and 3 days, what percentage of the energy eaten becomes production, and how does that compare with the 10% rule?
- How do production and respiration change if you assume larvae are 40% dry mass instead of using the measured value?
- Why does the wet mass lost by the sprout overstate what was eaten, and is the error larger at 15 °C or 25 °C?
