63. 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?
Answer: C
The plants increase chlorophyll production when exposed to sunlight.
The observation that plants kept in a dark closet have yellow leaves, while those on a windowsill have green leaves indicates that light exposure affects chlorophyll production. It is reasonable to conclude that the plants increase chlorophyll production when they receive sunlight, which is essential for the process of photosynthesis.
A) Plants make excess sugar when kept in the dark.
This option incorrectly suggests that sugar production occurs in the absence of light. While plants do produce sugar during photosynthesis, which requires light, they do not produce excess sugar when kept in the dark. Instead, the lack of light leads to a deficiency in chlorophyll and the yellowing of leaves.
B) The plants accumulate minerals from water when exposed to carbon dioxide.
This option does not directly relate to the observed difference in leaf color. While plants do absorb minerals and require carbon dioxide for photosynthesis, the accumulation of these elements does not explain the yellowing of leaves in the absence of light. The primary issue here is the lack of light impacting chlorophyll production, not mineral absorption.
C) The plants increase chlorophyll production when exposed to sunlight.
This option correctly identifies the relationship between light exposure and chlorophyll production. Chlorophyll is essential for photosynthesis and is produced in response to sunlight. The green leaves of the plants on the windowsill indicate healthy chlorophyll levels, while the yellow leaves of the plants in the dark indicate a deficiency due to lack of light.
D) The plants require oxygen in the open air to turn green.
This option misrepresents the role of oxygen in plant health. While plants do require oxygen for respiration, the color of the leaves primarily relates to chlorophyll levels rather than oxygen availability. The yellowing of leaves in darkness is more closely associated with insufficient light rather than a lack of oxygen.
Conclusion
The conclusion that plants increase chlorophyll production when exposed to sunlight is supported by the experimental results showing contrasting leaf colors. Options A, B, and D fail to connect the observed phenomenon to the critical factor of light, while option C accurately correlates chlorophyll production with light exposure, making it the most reasonable conclusion.