Herbicide Lab Report PDF

Preview

Summary

Lab report...

Description

Background and Hypothesis In this experiment spinach leaves were used to look at the specific mechanism of photosynthesis, specifically regarding how a certain drug would affect the process of photosynthesis in plants. This lab gives the possibility to differentiate between the two hypotheses that were being investigated. The task was to figure out if the drug (herbicide) being used acts before DCPIP takes the electron from Pq or after it takes the electron. The experiment that was set up was a series of test tubes containing different content combinations of spinach, water, buffer, light, DCPIP, and herbicide. The test tube containing a mixture of spinach leaves, water, DCPIP, and herbicide that was put under light was used to show if the drug acts before or after DCPIP takes Pq’s proton. If there was a color change in the test tube then that meant that the herbicide acted after DCPIP takes the proton and if there was no color change then that meant that the herbicide acts before DCPIP takes the proton. The rest of the test tubes and reactions were used as proofs to prove that nothing else occurs that would make this first experiment faulty by showing that DCPIP is able to be reduced and is only reduced by the photosynthetic material that was used in the lab. Figure

Key Factors: Photosystem II occurs when light is absorbed by chlorophyll molecules, which drives an electron obtained from water to a higher energy orbital. A chlorophyll molecule, P680, collects the energized electrons and passes them to plastoquinone (Pq). During this transfer is when the herbicide (Hypo 2) possibly acts to stop the electron transfer. Pq acts as an electron transporter, moving them forward to the cytochrome complex. DCPIP takes electrons from Pq and the herbicide (Hypo 1) possibly acts afterwards to impair the continuation of photosynthesis. Predictions The first hypothesis states that if there is a color change from the first mixture in the first test tube, then the herbicide acts after DCPIP takes the proton from plastoquinone (Pq). The second hypothesis states that if there was no color change in the mixture after being put under the light then the herbicide acts before DCPIP takes the proton from Pq. These two hypothesis elicit different predictions because a color change indicates that photosynthesis is occurring. Therefore if there is a color change, photosynthesis occurs and DCPIP is reduced and if the color remains the same, photosynthesis did not occur and DCPIP is oxidized.

Table Tube

Contents

Purpose

Observations (s) indicate timing

Interpretation

1

Spinach, water, light, DCPIP, herbicide, buffer

To see if the herbicide stops photosynthesis before or after DCPIP takes proton.

0min: 0.65 2min: 0.68 4min: 0.65 6min: 0.61 8min: 0.65 10min: 0.68 12min: 0.65 14min: 0.65 16min: 0.65

The absorbance was held steady indicating no color change, meaning the herbicide acts before DCPIP takes the proton.

2

Spinach, water, DCPIP, buffer, light

To test to see if the spinach discs are alive or not.

0min: 0.35 2min: 0.5 4min: 0.4 6min: 0.34 8min: 0.3 10min: 0.28 12min: 0.25 14min: 0.24 16min: 0.23

There was a change in absorbance meaning there was a change in color indicating that the spinach leaves were alive.

3

Herbicide, buffer, DCPIP, light, water

To test if anything else is reducing the DCPIP.

0min: 0.63 2min: 0.57 4min:0.55 6min:0.55 8min:0.55 10min: 0.55 12min: 0.55 14min: 0.55 16min: 0.55

The absorbance was held steady meaning there no significant change in color showing that there was no other reducing agent.

4

Spinach, herbicide, light, water, buffer, reduced DCPIP

To test to see if something is reoxidizing DCPIP

0min: 0.07 2min: 0.1 4min: 0.11 6min: 0.12 8min: 0.15 10min: 0.17 12min: 0.2 14min: 0.2 16min: 0.2

There was a slight shift in absorbance indicating that the DCPIP stayed reduced and nothing was re-oxidizing it.

5

Spinach, water, buffer, herbicide, DCPIP, darkness (no light present)

To test if photosynthesis is occurs without light.

0min: 0.59 2min: 0.59 4min: 0.59 6min: 0.59 8min: 0.55

The absorbance was held steady showing that photosynthesis was not

10min: 0.59 12min: 0.55 14min: 0.59 16min: 0.59

occurring.

Conclusion The results of test tube 1 of the experiment show that there was no significant change in absorbance over 16 minutes. This means that there was no color change of the solution, so the second hypothesis of the herbicide acting before DCPIP whisks an electron off is correct. The lack of color change, which would be blue to clear, shows that DCPIP could not steal electrons from plastoquinone and was not reduced over the duration of the experiment. When the isolated chloroplasts were exposed to a light source, electrons transferred through the electron transport chain could not reach the DCPIP electron acceptor from the plastoquinone complex. Instead, a drug, the herbicide, inhibits photosynthesis from continuing by blocking the electron flow from Photosystem II to plastoquinone. The results refute the first hypothesis, which would have proven herbicide works after plastoquinone and before Photosystem I with a solution color change. The control test tubes ensured that nothing out of the ordinary occurred. Test tube 2’s purpose was to check if DCPIP allowed photosynthesis to continue and to check that the spinach extract was alive. Because the absorbance values decreased over time, DCPIP was being reduced from plastoquinone. With test tube 3, there was no significant change in absorbance, meaning nothing, other than the spinach chloroplasts, was reducing DCPIP. In test tube 4, since the absorbance values did not decrease, no factors were re-oxidizing DCPIP (i.e. stealing electrons from it). Lastly, test tube 5’s results show that in the absence of light, DCPIP does not get reduced without the occurrence of photosynthesis....