Final answer:
The mass of a plant mostly comes from carbon dioxide from the air and water absorbed from the soil, not from the soil itself.
Step-by-step explanation:
Understanding Plant Mass Acquisition
The mass of a plant comes primarily from the elements it absorbs from its environment. Through the process of photosynthesis, plants take in carbon dioxide from the air, which is then transformed into organic matter that contributes to the plant's mass. Plants also require water absorbed via their root system from the soil, which is essential for metabolic functions, structural support, and photosynthesis. Contrary to common belief, the soil contributes much less to the plant's mass compared to the components absorbed from air and water. This is evident from observations that even completely dry plant matter, devoid of water, retains substantial mass.
Thus, when assessing the experiment and considering the student's question, it can be concluded that the mass of a plant mostly comes from the carbon dioxide in the air and the water absorbed from the soil. Although plants utilize nutrients and minerals from the soil, these elements do not make up the bulk of a plant's mass.