Plants, light and a conclusion

A fictional school garden compares similar plants in two locations over several days. The sunnier location also receives more water, and the plants are not randomly assigned. A learner concludes that the observations prove light alone caused every difference in growth. Another learner claims plants cannot respire because they perform photosynthesis. The class has permission to record plant observations but has not measured every resource or condition affecting growth. The teacher asks students to distinguish the biological processes from the limits of this particular comparison. No missing growth measurements, exact nutrient values or laboratory procedures are supplied in the exercise, and the plants are not evidence about all ecosystems.