Question

Your neighbor, an amateur scientist, wants to know where growing plants get the materials necessary for their growth (increase in size over time). She conducts an experiment in which she plants a tree seedling weighing 2 kilograms (kg) in a barrel filled with 91 kg of soil and then waters the tree regularly. After five years, the tree weighs 77 kg and the soil weighs 90 kg. Because the tree had gained so much weight and the soil had lost so little weight, she concludes that the tree gained all of its additional weight by absorbing the water she had added to the barrel.

Is your neighbor's conclusion correct or incorrect?  Explain why she is correct or incorrect using information that you have learned from this course.

Answer 1

The Neighbour's conclusion is incorrect.

Though plants require water for carrying up nutrients from soil which are necessary for their growing process and physiological conditions, yet its growth growth of biomass is mainly dependent on its production of food through photosysthesis. This process of photosynthesis requires carbon dioxide collected from air and produces glucose with the help of chlorophyll in the leaves or other green organs, in present of light. The energy from light is trapped in this process in the form of food, which increase the biomass of the plant, that shows the increase in height and the weight of the tree. A part of synthesized glucose is also used for respriration to release the energy required to run the physiological processes, including cell division that results into growth.

The nutrients taken from soil is ustilized in different other processes like - Mg is a component of chlorophyll, N is important component of protein etc., however though such nutrients are highly important yet needed only in a very small quantity. Water is used to transport such nutrients from soil to organs of plants and water is also used for production of glucose by supplying the electron that is required to run the photosynthesis process. But itself water is not consumed to form the biomass, but the carbon from carbon dioxide gas from air is the major component for the growth of the tree.