Van Helmont, chloroplasts and the light stage
Answers are for parents and teachers.
1
Explain Van Helmont’s experiment in four sentences.
He planted a 2.2 kg willow in 90 kg of dry soil and watered it for five years. The tree weighed 75 kg and the soil lost only about 55 g. So the tree’s mass did not come from the soil. Later work showed that carbon dioxide from the air is needed too.
2
Draw a chloroplast as boxes and label the stroma and the grana.
A large box (double membrane) containing a fluid (stroma) and stacks of small flat boxes (grana).
3
Why is red or blue light better for photosynthesis than green light?
Chlorophyll absorbs red and blue light strongly and reflects green.
4
Name two parts of a plant that photosynthesise and one that does not.
Leaves and green stems do; roots in the soil do not.
5
Find the mistake: “Plants take all their mass from the soil.”
Most of the dry mass is carbon from carbon dioxide in the air; water also contributes.