Question

Jan Van Helmont hypothesized that in order for a tree to grow and gain mass, it must find food somewhere else. He carefully weighed a tree and the soil that he wanted to plant the tree in. Time passed, and the tree grew. After five years, he reweighed the tree, which had grown quite large, and the soil. To his surprise, the soil weighed basically the same amount, suggesting to Jan that the plant couldn’t be gaining mass from the soil. If you were Jan, what would you do next to try to figure out what the plant was consuming for food?

Answer 1

Plants are sedentary forms which prepare their own food using sunlight water , air and minerals from soil. This is an established fact. They are autotrophs and prepare their own food. Do not consume food from the surroundings. Plants absorb water and minerals from soil , that is why the weight of the soil does not change.

Because the weight of the soil did not decrease, Jan must have concluded that the plant did not consume the food present in the soil. If it is not soil, then the air must be providing some thing to the soil. So plant can be kept in an enclosed place not having CO2 ,by placing KOH in its vicinity for some days. The purpose of KOH is , it absorbs CO2 from the air present around. If it is continued for some days, the plant will not be able to prepare food and growth of the plant gets effected. The plant also can be covered in such a manner that it does not get sun light for some days. This also affects the growth of the plant. Suppose in another experiment, Jan can stop watering the plant completely and see if the plant grows. These small experiments done by Jan will prove that plants do not consume food present in the soil. They prepare food by absorbing raw materials like CO2, water from the soil and absorbing energy from the sun light.