Answer :
Final answer:
The variable that needs control in the experiment is the nitrate concentration to accurately study its impact on leaf size.
Explanation:
The variable that would need to be controlled for the experiment is the nitrate concentration. In this case, it means keeping the nitrate levels consistent across the experimental conditions to accurately assess the impact on leaf size.
Controlling for variables like volume of water given to the tree or species of tree would help ensure that any observed effects on leaf size are truly due to the nitrate concentration and not influenced by other factors.
Controlling nitrate concentration allows isolating its specific effect on leaf size in oak trees.
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