Photosynthesis/Light Reaction Lab

Purpose

The purpose of this lab was to prove that light and chloroplasts are required for the light reactions of photosynthesis to occur.

Introduction

Photosynthesis is a way for plants to make their own food using direct sunlight. Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes. Leaves are the major locations of photosynthesis; where chloroplasts are located. In order for plants to produce sugar and release oxygen, they must first go through the light reactions. Chloroplasts split water into hydrogen and oxygen, incorporating the electrons of hydrogen. Light is then absorbed and the energy is used to drive electrons from water to generate NADPH, a stored sugar. When the electrons are excited, they burst upward and are caught by an electron accepter and then slowly released down via the electron transport chain. It is important to understand the job of the electron acceptor. DPIP can also be used instead of NADP. Every time the electrons in the chloroplast become excited, they will reduce DPIP. This will cause DPIP to change from blue to colorless. 

Methods 

Pipette 5mL of 100% dye solution into the 1st test tube, and pipette 2.5 mL of distilled water into the remaining 5 test tubes. 

Then transfer 2.5 mL of dye to the 2nd test tube and mix well. 

Transfer 2.5 mL of solution from the 2nd rest tube into the 3rd test tube and continue the process for the remaining test tubes. 

We filled a cuvette with solution from test tube 1 and read the Abs. and %T. We continued the same thing for the rest of the text tubes.

Graphs and Data

Discussion

In this lab, light and chloroplasts are proven to be needed for light reactions in photosynthesis. DPIP is used instead of NADP, which is the electron accepter in this experiment. When the electrons become excited, they will reduce the DPIP supply. These electrons come from the breaking down of light energy and water. The reduction of the DPIP supply will cause the solution to change from blue to clear. Due to the DPIP reduction, light transmittance is given off. This can be measured using a spectrophotometer, which measures the percentage of light transmittance. When the DPIP is placed in darkness, there is no reduction in it because the electrons cannot be excited because they do not have any light to excite the electrons. When the chloroplasts were boiled, it denatured the protein molecules, which also stopped reduction in the DPIP. There was a difference in percent transmittance of the unboiled chloroplasts that were in the light and the dark. This is because in the dark cuvette, there was no light, which meant that there was no light energy and therefore no breaking down of light and water which meant that the electrons could  not be excited. In the lighted cuvette, there was light energy, which aloud breaking down of light and water and therefore there were excited electrons.

Conclusion

The experiment preformed showed that chloroplasts and light are necessities for light reactions in the photosynthesis process. All in all, the outcome of the data proved this point true. It showed all factors of boiling, denaturing, and darkness, which did not allow light reactions to occur.