Effect of light intensity on the rate of photosynthesis

In an experiment that tested the effect of light intensity onthe rate of photosynthesis, we do not run a control tube in theexperimental setup. that is not every good scentific practice isit? why is a control important in an experiment? how would youdesign a control for this experiment? be specific. if theexperiment data shows that the conrol tube geerated pressure andhad a measurable rate of photosynthesis just like the experimental tube did, whatwould this fact tell you about the experiment?

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