solve the CHAPTER MYSTERY

OUT OF THIN AIR?

Most plants grow out of the soil, of course, and you might hypothesize, as Jan van Helmont did, that soil contributes to plant mass. At the conclusion of his experiment with the willow tree, however, van Helmont discovered that the mass of the soil was essentially unchanged, but that the tree had increased in mass by nearly 75 kilograms. Van Helmont concluded that the mass must have come from water, because water was the only thing he had added throughout the experiment. What he didn't know, however, was that the increased bulk of the tree was built from carbon, as well as from the oxygen and hydrogen in water. We now know that most of that carbon comes from carbon dioxide in the air. Thus, mass accumulates from two sources: carbon dioxide and water. What form does the added mass take? Think about the origin of the word carbohydrate, from carbo-, meaning “carbon,” and hydrate, meaning “to combine with water,” and you have your answer.

1. Infer Although soil does not significantly contribute to plant mass, how might it help plants grow?

2. Infer If a scientist were able to measure the exact mass of carbon dioxide and water that entered a plant, and the exact mass of the sugars produced, would the masses be identical? Why or why not?

3. Apply Concepts What do plants do with all of the carbohydrates they produce by photosynthesis? (Hint: Plant cells have mitochondria in addition to chloroplasts. What do mitochondria do?)

4. Connect to the Explain how the experiments carried out by van Helmont and Calvin contributed to our understanding of how nutrients cycle in the biosphere.