BIO 103
Introduction:
Plant cells photosynthesize to produce glucose. By doing this, light energy, coming from the sun, is transformed in chemical energy, glucose. Oxygen is also produced from carbon dioxide and water. The process occurs by light dependent reactions (in thylakoids) and dark dependent reactions (in the stroma). In the light, plants produce energy molecules, such as ATP and NADPH; in the dark, they use those molecules to fix the CO2. The excess of glucose during photosynthesis can convert into starch.
Purpose:
The purpose of this experiment was to determine the differences between leaves from plants exposed to the sun and ones that are left in the dark.
Question:
Is there any difference between leaves exposed, for two days, to the light and to darkness?
Hypothesis:
Leaves present more starch when they are exposed to the sun, rather than left in the dark.
Adding iodine will produce varied results with respect to the two leaves.
Materials:
Leaves from dark.
Leaves sun exposed.
Benson burner.
Iodine.
2 Petri dishes.
2 beakers.
Boiling water.
Methanol.
Forceps.
Procedures:
We placed water to boil in two different beakers. When it was boiling, we put one leaf from the plant that had been exposed to the sun. In the other beaker, we put one leaf that was left in the dark for two days. We left them boiling for 10 to 15 minutes.
Leaves were taken from the water and we put them in boiling methanol.
At the end of the boiling period, we transferred each leaf to an individual petri dish and filled it with iodine.
We recorded the presence or absence of black spots in each leaf, in order to see the difference between them.
Results: (Diagram)
Discussion:
The leaf that was exposed to the sun showed dark spots when iodine was added. This result is related to the starch that is present in the leaf when it was exposed to the light, due to the photosynthesis process. The boiling process in water helped break the cell wall in the leaves cells. On the other hand, methanol removes the pigments from leaves, which are mainly present in those exposed to the sun, but not in the one that was on the dark for two days. These results are in accordance with my hypothesis because leaves exposed to the sun exhibited starch. A difference was found between the leaf exposed to the sun and the one that was on the dark.
Conclusion:
We concluded that leaves exposed to the sun photosynthesized and had starch on it, developing the dark spots when iodine was added. This is contrary to leaves left in the dark for two days, where photosynthesis did not occur, and dark spots did not develop.
