Could someone help me with this question :)

Mario performed an experiment to determine if photosynthesis was affected by the amount of light that a plant received. what could he have done to increase the validity of his data? reduce the number of plants. remove the 1 hour group. add a 0 hours control. measure the oxygen in liters

When does dna replication(make a copy of itself)?

Which organelle breaks down sugar molecules that supply energy to the cell ?