Year 8 can recite the word equation, but many still believe a plant's mass comes from the soil. The teacher shows a photograph of a mature oak and asks in Mentimeter where most of its mass came from: the soil, water, the air or sunlight. Answers come in anonymously and the board shows the spread, and rather than give the answer, the teacher shares Jan Baptist van Helmont's willow experiment, published in 1648 after his death, in which a 5-pound willow grew to about 169 pounds in five years while its 200 pounds of dried soil lost about 2 ounces. Pairs argue about what van Helmont concluded, that the mass came from water, and what he missed, the carbon dioxide from the air, and then everyone votes again. The teacher puts the two results side by side, asks two students who changed their answer to explain why, and spends the last part of the lesson with the students still choosing soil, tracing the carbon in glucose back to the air.
Tools: Mentimeter Nine ideas for your own version in Generate
This page is one of a growing set of PICRAT examples by cell, subject and grade. Page maintained by Andy Perryer.