Pond snails (Lymnaea stagnalis) feed on Elodea (water weed). In an ecological investigation, 12 pond snails were kept in an aerated aquarium containing 620 grams of Elodea for ten days.
A researcher recorded the total wet mass of the Elodea and the total wet mass of the pond snails at the start and at the end of the ten-day period. The results are shown in the table below.
| Mass in grams at start | Mass in grams at end | |
|---|---|---|
| Elodea | 620 | 280 |
| Pond snails | 80 | 115 |
Explain why the decrease in the mass of the Elodea is much greater than the increase in the mass of the pond snails.
