A biologist ground up some plant leaf cells and then centrifuged the mixture to fractionate the organelles. Organelles in one of the heavier fractions could produce ATP in the light, whereas organelles in the lighter fraction could produce ATP in the dark. Explain these results. What is present in the light fractionate that is absent in the heavier fractionate? What is present in the heavier fractionate, that is absent in the light fractionate? Why are these components important to a clear explanation?

1. The heavy fraction produces ATP in the presence of light which means that the light is required for the synthesis of ATP and the organelle associated with the light is Chloroplast.

2. The lighter fraction produces ATP in the dark condition that means no light is required for ATP synthesis and the organelles associated with this is known as Mitochondria.

These organelles can be predicted based on their role in the ATP synthesis and the requirement of light condition for ATP synthesis.

Thus, Chloroplasts and mitochondria is correct.