Question 4
Iodine solution is added to a decolourised leaf and it turns blue-black. What does this show?
The right answer is the one marked above.
Starch is present, so photosynthesis took place in that part of the leaf. Blue or dark purple is the positive result.
The result need not be the same across the whole leaf. Part of a leaf turning dark while the rest does not is not a failed experiment — it is the method of the next three skills.