The Mystery

The Mystery: follow the evidence

A seed may be tiny, yet the plant that grows from it can have a much greater mass. Where did the added matterAnything made of atoms that has mass. come from? Imagine weighing a seed, its soil (organic matterAnything made of atoms that has mass.), and the whole plant over time. A change in plant mass is an observation; an explanation must account for the atomsTiny building blocks of matter that can be rearranged into new substances. that entered the plant.

Plants take in carbon dioxideA gas in air that supplies carbon atoms used to build sugars. (CO₂) from the air and water (H₂O) through their roots. With energyThe ability to cause change or make processes happen. from sunlight (electromagnetic energyThe ability to cause change or make processes happen.), photosynthesisA process in which plants use light energy to make sugar from carbon dioxide and water. rearranges atomsTiny building blocks of matter that can be rearranged into new substances. from these substances into sugars, including glucoseA sugar made by plants that stores chemical energy. (C₆H₁₂O₆). Those sugars can become part of other plant molecules. Sunlight supplies energyThe ability to cause change or make processes happen., but its light is not itself the matterAnything made of atoms that has mass. that makes the stem larger.

Soil provides minerals and sometimes organic matterAnything made of atoms that has mass., but a growing plant does not obtain most of its new mass directly from soil. A convincing investigation would measure inputs and outputs as well as plant growth. In today’s greenhouse model, change the carbon dioxideA gas in air that supplies carbon atoms used to build sugars. available while keeping light and water alike. The model can show a growth pattern; it cannot measure the exact mass of every atom.