Final answer:
A scientist in 1642 discovered that a plant's mass primarily comes from the air, specifically carbon dioxide, due to the process of photosynthesis. The experiment involved measuring the mass of a willow tree and the soil in which it grew, with only water added, over five years. The weight measurements taken would be relative to Earth's gravity, and scales would show different measurements on the Moon.
Step-by-step explanation:
The experiment conducted in 1642 by a scientist to evaluate where a plant's mass comes from involved growing a willow tree in a pot and adding only water for five years. The scientist recorded the weight of the tree and the weight of the dried soil at the beginning and the end of the experiment. This study demonstrated that the mass of a tree primarily comes from carbon dioxide in the air rather than the soil or water. This is because trees undergo photosynthesis, a process in which they convert carbon dioxide and water into glucose and oxygen, using light energy. The increase in the mass of the tree over time can be attributed to the carbon atoms from carbon dioxide being incorporated into glucose which becomes part of the plant's structure.
Regarding mass and weight, on Earth, 1 lb is equivalent to a mass of 0.4536 kg. This highlights the difference between mass, a measure of the amount of matter in an object, and weight, the force exerted by gravity on that mass. In the experiment with the willow tree, the scientist would have used a scale to measure weight, but this can then be converted into mass units. How scales measure mass on Earth can differ from how they would measure it on the Moon due to the difference in gravitational pull.