Exercise 1 solution

Each step passes on about 10 per cent, so each step up needs 10 times as much below.

Five levels (phytoplankton, zooplankton, small fish, large fish, top predator) means four transfers: 10 x 10 x 10 x 10 = 10,000 kg of phytoplankton for 1 kg of top predator.

Three levels (phytoplankton, krill, whale) means two transfers: 10 x 10 = 100 kg of phytoplankton for 1 kg of whale.

The shorter chain is 100 times more efficient, which is how a whale can be so large while feeding low in the food web.