Answer:
Step-by-step explanation:
It is likely that the oxygen levels decreased in the foil-covered test tube over time due to cellular respiration by the plant in the tube. Plants undergo cellular respiration just like animals do, which involves taking in oxygen and releasing carbon dioxide as a byproduct. When the plant is placed in a sealed container such as a test tube, the oxygen that is being released by the plant during photosynthesis will eventually be depleted as it is used up in cellular respiration.
In addition, the foil covering the test tube would have prevented new oxygen from entering the tube, leading to a decrease in the overall oxygen levels. This decrease in oxygen levels would continue until the plant is no longer able to perform cellular respiration due to lack of oxygen. This process is a natural part of the carbon cycle and occurs in both natural and controlled environments.