Question: how many joules of energy are available to convert into new biomass?
Answer: During the same time period, another 320 joules of energy is lost as heat or utilized in metabolism. This leaves 180 joules for production of new tissues as the caterpillar grows. Dividing 180 by 1000 gives a value of 0.18, meaning that only 18% of the energy taken in by the caterpillar is converted into biomass.