Variables:
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Independent Variable(s): Type of Alcohol (Methanol, Ethanol, 1-Propanol) and Alcohol Concentrations (0%, 10%, 20%, 30%, and 40%)
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Dependent Variable(s): The amount of red pigment released ( Absorbance)
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Controlled Variable(s): room temperature, test tubes, beetroot, colorimeter, lab- pro, and power supply.
Materials/Equipment: See Lab Handout
Procedure: See Lab Handout
RESULTS
Data Collection:
Table 1: The amount of damage various alcohols cause to cell membranes
Fig. 1 - This table describes the data we collected in our individual group(s).
Table 2: The amount of damage various alcohols cause to cell membranes at a given Concentration.
Fig. 2 - This table shows the data for all 4 groups, it includes their average of each groups reading at each concentration of each alcohol.
Data Analysis:
Graph 1: Percent Alcohol vs. the Amount of pigment (Absorbance)
Sample Calculations: (Table 2)
Average = sum (x_i) / n
Methanol – at 0 % -
Average = (0.128 + 0.130 + 0.061 + 0.104) / 4 = 0.105
Ethanol – at 10 % -
Average = (0.226 + 0.054 + 0.074 + 0.193) / 4 = 0.136
1- Propanol – at 20 % -
Average = (0.579 + 0.091 + 0.090 + 0.442) / 4 = 0.300
Graph 2: Concentration of Alcohol vs. Average Absorbance
Conclusions & Evaluations
Based on the data above it can be concluded that the hypothesis was supported, and propanol did the most damage to the cell membrane followed by ethanol and then methanol with the least damage to the membrane. From the graphs it can also be concluded that the highest concentration causes the most damage to the cell membranes, which was 40% propanol followed by 30 %, 20%, 10% and 0%. Although there might be few errors seen in the graphs and data, the most damage was done at 40 %. Through the results it can be seen that high alcohol concentrations change the membrane structure and force transmembrane proteins into unfavorable conformations. Thus, proteins cannot function and yield drops noticeably. The higher the concentrations, the more protein damage and then more membrane damage.
There are various sources of errors and limitations observed in this lab. The use of different pipettes was necessary for this lab, and there could have been errors while labeling or pouring the different materials needed. The size of the beet root squares could have been a bit inaccurate and might have included some ragged edges. There were few errors in the data as some of the squares of beet roots were punctured while stirring the alcohol solutions. It was necessary to keep all cuvettes wiped, clean and dry on the outside with a tissue, this could have also caused some minor errors while collecting the data. Also the air bubbles in the alcohol solutions could have caused a few errors throughout the lab. The number of drops would have also caused some errors in the experiment, and observing the time with the use of stopwatches could have included random and systematic errors. Some values may be more accurate than the others, but most are imprecise. Also when handling alcohol, it should be done with extra care and you should always follow the safety rules and regulations. Errors occur in every experiment, which makes it necessary to do more trials. I thought that our group could have done more trials, but due to shortage of time we couldn’t. For future improvements I would suggest that probably do more trials, which would decrease the minor errors, and also label the beakers/tubes carefully. Overall, I think that the lab was proficient and no more further improvements would be needed.
QUESTIONS
1.) Ethanol damaged membranes more at low concentrations. At 10 % alcohol, there was more propanol pigment released into the solution compared to the 1- propanol and methanol.
2.) 1-Propanol seems to affect membranes the most, as there is more pigment (cellular damage) at any concentration of alcohol.
3.) For all three alcohols, the percentage of alcohol that was the most damaging was 40%.
CHALLENGE QUESTION
It is said that the larger the size of an alcohol molecule, the greater the extent of membrane damage. 1-Propanol, a three carbon molecule, is larger than ethanol, a two carbon molecule and methanol, a one carbon molecule. Lipids can be made of hydrocarbon chains, which are non-polar. As the alcohol increases its length, it becomes less polar than smaller alcohols. Then it is allowed to combine with lipids to a greater extent. Since the OH branch of the alcohol mixes with water, the longer alcohols can mix with both lipids and water. This tends to dislocate the cellular membrane. For this reason, larger alcohols might cause wide-ranging membrane damage.
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