In this problem, we are asked to explain why the pH of the suspension solution goes down during dark periods.
When chloroplast preparations are brought into the light, we see a shift in pH of the solutions; these plant organelles are the site of photosynthesis, and thus react to the presence or absence of light. The biochemistry separates the production of energy from the production of sugar inside the chloroplasts - energy production requires the light, but sugar production does not.
During the dark periods, the proton pumps in the chloroplast cease functioning; they are no longer breaking down water into protons that can drive the production of adenosine triphopshate (ATP). ATP synthase (the enzyme responsible for the production of ATP) continues to pump protons back across the membrane into the solution around the chloroplast until equilibrium is established. This increase in protons back into the solution drives the pH down.
In this problem, we are asked to draw a flow chart for the chloroplast preparation steps in this experiment.
The isolation steps require a series of steps, mostly involving centrifugation at various speeds, and then several chemical isolation steps to select just for the chloroplasts.
The flow chart would be as follows: Thus, chloroplasts can be isolated from leaf extracts.
In this problem, we are asked to explain chlorophyll extraction in terms of chemistry, explaining why acetone is a better solvent for the extraction, and what steps could be taken to improve the yield in the extraction step.
Chlorophyll, as an organic molecule, is largely non-polar, and therefore is more soluble in non-polar solvents such as acetone; acetone will disrupt the pigment-protein complex as well.
To improve yield, we could combine multiple extractions into a larger starting pool; this would require more starting material (leaves).