1. Photosynthesis
aim- to determine whether chlorophyll is necessary for starch formation.
hypothesis- the covered leaves will reveal that starch is present and the variegated leaves will react
to the iodine wherever there is no chlorophyll present.
method
1. Cover out 3 leaves from a tree for 24-48 hours
2. Remove leaves
3.soak in alcohol boil.
4. after 5-10 minutes the leaves should look uniformly pale. The liquid would have taken on a green
colour as the pigment from the leaves dissolve
5. Remove leaves from alcohol and place on a paper towel
7. Dip each leaf in hot water, in order for them to soften
8. Cover each leaf with iodine solution in a beaker and allow them to stand for a minute.
9. Remove leaves from beaker, gently wash off the iodine solution. Note that iodine turns blue/black
if starch is present.
Result
The leaves did not show that starch was present. The main reason why the result did not fit the
hypothesis is because the leaves were not covered for long enough. The variegated leaves appeared
yellow after the experiment as there was no chlorophyll present. The spots where there was starch
reacted to iodine and turned black.
Discussion
The results that were revealed by the practical did not support the hypothesis. The main factor that
led to this would be that the leaves were not covered for long enough. The leaves did not change in
texture or colour within the two days they were covered. The variegated leaves lost all their
chlorophyll and turned yellow. The spots where starch was present turned black, and this supported
the hypothesis
Conclusion
the leaves should have been left covered for longer. The presence of starch within the covered
leaves was not identified through the practical therefore it is unknown whether chlorophyll is
necessary for starch formation. However the starch within the variegated leaves reacted with the
iodine and turned blue/black.
