Biology: Concepts and Investigations 2nd Edition by Mariëlle Hoefnagels

Exercise 31

One of the first investigators to explore photosynthesis was Flemish physician and alchemist Jan van Helmont. In the early 1600s, he grew willow trees in weighed amounts of soil, applied known amounts of water, and noted that in 5 years the trees gained more than 45 kg, but the soil had lost only a little weight. Because he had applied large amounts of water, van Helmont concluded (incorrectly) that plants grew solely by absorbing water. What is the actual source of the added biomass? Explain your answer.