At the end of an experiment, students observe that the plants kept in a dark closet have yellow leaves, but those kept on a windowsill have green leaves. Which of the following is the most reasonable conclusion on the basis of the experimental results?

While it is true that plants can undergo processes like respiration in the dark, they do not produce excess sugar without light for photosynthesis. In fact, without sunlight, the plants are unable to synthesize sugars effectively, which would not explain the yellowing of leaves observed in the dark.

This choice suggests a correlation between mineral accumulation and carbon dioxide exposure, but it does not directly address the color change of the leaves. The yellowing of leaves is primarily linked to the lack of chlorophyll due to insufficient light, rather than mineral uptake or carbon dioxide levels.

While oxygen is indeed necessary for cellular respiration, the color change observed in the plants is related to chlorophyll production in response to light. This choice misattributes the leaf color change to oxygen availability rather than the light's role in photosynthesis and chlorophyll synthesis.