What affects membrane permeability

Published: 2018-04-10 21:20:19
1896 words
7 pages
16 min to read
Wesleyan University
Type of paper: 
This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

Cell Membrane Permeability Practical Investigation


This experiment investigates the effect of changes in pH, alcohol and different concentrations of detergents on beetroot membrane. If the extreme levels of pH would degrade the beetroot cell membrane, the experiment would prove that different solutions react differently.


Cell membranes are the entry points for liquid solutions. They allow the solutions to get into the cell. It comprises of a lipid bilayer, made up of phospholipids. Since phospholipids are amphipathic, they demonstrate both hydrophilic (extends towards the water) and hydrophobic (tries to avoid the water) properties making them shape bilayers in water-based solutions. Because of the membrane hydrophobic and hydrophilic spots, the layer is specific on its porousness of particles. Whenever particles, molecules, or atoms are made through the disassociation of ionic compounds, the particles, gives a particular charge.

What is more, since the membrane is impermeable to a couple of substances aside from through channel proteins, vital solutes can be secured. Nonetheless, some conditions such as the pH, temperature, and introduction to natural solvents may obliterate the cell membrane's structure and henceforth hinder its capacity. Estimations are done through absorbance readings by the red color from the betacyanin that was spilled from the vacuole to the surrounding. The purpose of this lab is to investigate the effect of various concentrations, alcohol, and detergents on beetroot membrane.

Aim of the permeability of cell membrane investigation

The aim is to investigate the changes in pH, a concentration of detergent solutions and alcohol affecting the structure of the cell membrane of beetroot cells.


The extreme levels of pH would degrade the cell membrane of the beetroot cells.

Dependent Variable

The dependent variable in this investigation was the amount of color in the solution.  The dependent variables are measured by sight.  That everyone has the same perspective of the color pink.

Independent Variable

The independent variable in this investigation was the solutions in the petri dishes.

Controlled Variable

The controlled variable was the time and the size of the beetroot slices to make it a fair experiment.


·         11 petri dishes

·        Cork borer (d = 1 cm)

·        Colorimeter (if available)

·         Waterproof pen

·        Marker pen

·        Electronic balance

·         Paper towel

·        Solutions of pH 2, 4, 6, 8 and 10

·        Ruler

·         Forceps

·        Distilled water

·        1%, 25% and 50% solutions of alcohol

·         Knife

·        Solutions of 1% and 5% detergent

·        Beetroot with skin removed

Method to determine factors affecting cell membrane permeability

A knife was used to cut off the beetroot at the top and bottom. Then a cork borer was pushed into the beetroot and withdrawn. The cylinder remained inside, so a smaller cork borer was used to remove it. After collecting several uniform cylinders, the beetroot was cut into small pieces of 2mm length each. The cylinders were rinsed in running water for 5 minutes, then a paper towel was laid on a bench, and 11 clean Petri dishes were placed on top. The lids of the Petri dishes were labeled from 1 to 11, and the towels were labeled with the solutions’ names and group names.

Petri dishes pictures

Using forceps, 5 beetroot cylinders were placed in every petri dish. Appropriate dishes were then filled with the solutions, so the cylinders were completely covered by the solutions. Observation of the color was made immediately, after 1 hour, and after 24 hours. The observations were recorded in Table 1 shown below. The intensity of the color was also measured using a colorimeter and the results recorded on a scale of 1-5. The results were compared with those of other groups.

Biology experiment results

Membrane permeability investigation results

As the concentration of different solutions increased, a discernible pattern of the absorbance readings ascended close to the rise of higher concentration for every one of the graphs with the exception of distilled water. In the alcohol absorbance readings, the concentration of 50% got the most noteworthy absorbance of 4. The second most astounding of the alcoholic solutions was a concentration of 25% and permeability at 2. Of all the three alcohol solutions; the most minimal was at a concentration of 1% and permeability of 1.5. Next, the concentration of pH8 got its most elevated absorbance at 1.5. The detergent got its most noteworthy absorbance readings of 5 in a concentration of 1%. The concentration of 0%, distilled water in every one of the three tables, got the most reduced absorbance of 1. A recognizable change in the concentrated solutions absorbance readings was from the colossal distinction at its concentration at pH2 and pH8. Another perceptible component was the alcohol absorbance readings, which had a graph that consistently climbed. At 1 %, the absorbance reading was 1.5, and after that, it expanded to 4 at 25 %, then went to 5at 50%.

Effect of alcohol on the membrane integrity

Fig. 1.1 The effect of various alcohol concentrations on the beet membrane integrity

Effect concentrations on the beet cell membrane

Fig. 1.2 The effect concentrations on the beet cell membrane

Table 1: Colour intensity of solutions over time


Table observed

Colour intensity of the solutions (arbitrary units)


Distilled water




pH 2

pH 4

pH 6

pH 8

pH 10






At the start












After 1 hr












After 24 hrs












Table 2: Class colour intensity of solutions over time

Solutions colour intensity

Analysis of cell membrane permeability factors investigation results

1.      Which dish was used as the control? Did any changes occur in this dish?

The dish used as the control was the distilled water.  There were no changes that occurred in this dish because it was the control.

2.      What is independent variable in this investigation?

The independent variable in this investigation was the solutions in the petri dishes.

3.      What are the dependent variables? How would you measure it? What assumption do you make when choosing this method of measurement?

The dependent variable in this investigation was the amount of colour in the solution.  The dependent variables are measured by sight.  That everyone has the same perspective of the colour pink.

4.      What other variables need to be controlled?

Other variables that needed to be controlled was the time and the size of the beetroot slices to make it a fair experiment.

5.      What is the ideal pH range for the beetroot cell membrane? Why do you think that the membrane leaked at pHs outside this range? (That is, which membrane component was affected by exposure to these pH solutions? Why?)

The ideal pH range for the beetroot cell membrane is between 4 to 10 because the least amount of colour variation.  The membrane leaked at pHs outside this range because the membrane was broken down by the solutions.

6.      In which pH solution did the pigment leak out the most?

The pigmentation leaked out the most in the pH solution 2 because it is acidic and broke down the cell membrane.

7.      Which percentage of alcohol affected the membrane the most?

The percentage of alcohol affected the membrane the most was 50% because it is the most concentrated out of the alcohol solutions.

8.      Which percentage of detergent affected the membrane the most?

The percentage of detergent affected the membrane the most was 1%.  Unsure why as we assumed the 5% would do the most damage.

9.      Which solutions affected the membrane immediately?

The solutions affected the membrane immediately was 50 % alcohol and 5% detergent.

10.  From which part of the beetroot cell is the colour leaking out?

The part of the beetroot cell that was leaking colour out was the cytoplasm.

11.  How did the beetroot cylinders appear after 24 hours in distilled water? Explain.

The beetroot cylinders swelled up after 24 hours in distilled water.  Because the water diffused into the beetroot cell.

What affects permeability of cell membrane discussion

The purpose of the experiment was to investigate the effect of different concentrations of detergents, alcohol, and pH solutions on the cell membrane of a beetroot. It was hypothesized that increasing the concentration of various solutions led to high absorbency rate of the cell membrane. However, the results discredit the theory since a portion of the solutions failed to deliver a higher permeability readings when the concentration was increased. When the detergent solution is compared with the alcohols, it is clear that the detergent caused a higher permeability. In any case, contrasted with the early readings, the permeability ought to have expanded bit by bit; the chart rather gave a fluctuating reading as concentration expanded. Moreover, the detergent was an amphipathic/amphiphilic atom, which means; it contains both hydrophilic and hydrophobic areas that could fulfil the polarities of the phospholipid bilayer making a less demanding porousness. Within the bilayer, amphiphilic particles make micelles which disturb the hydrophobic spots making them easier to dilute which then breaks the phospholipid bilayer. In this way, this demonstrated that the detergent was additionally harming to the cell membrane. Then again, despite the fact that alcohol solutions are not amphiphilic, the compound structure of the alcohols could at present upset the cell membrane depending on to what extent the hydrocarbon chain is.

In this investigation, a few inconsistencies were available in the exploratory outcomes because of trial errors. One conceivable source of test mistake could be the extent of the beets or potentially stacking the beet membranes on the cone-like cutter. The impact of this was the surface zone could be decreased fundamentally, so the measure of betacyanin spilling out of the beet cells may have had been corrupted. Notwithstanding that, the thicker the bit of beet, the more betacyanin was accessible to spill out. Another mistake could have been the cross-tainting between the various solutions. Amid the test, a similar pipette was utilized as a part of the refined water solution and salt solutions; this prompted to the defilement of the test, consequently, changing its concentration. Finally, the spectrophotometer had not been turned on when entering the lab so it might add to errors displayed in this trial.

To enhance this lab, more trials could have been done to assess the beet membranes on the distinctive solutions. More trials mean not so many mistakes but rather more exact outcomes. Beet membranes that have a similar size and shape could have given better result on the distinctive solutions.


This experiment proves that cell membrane reacts differently to different solutions. The class results are too inclusive are too varied in opinions. The cell membrane is made out of a phospholipid bilayer that has a particular porousness which specific particles and atoms can cross. With both a hydrophilic head and hydrophobic tail spots, extremity makes a part of porousness. With the diverse strategies for entrance and harm to the atoms, one component continues as before of the considerable number of solutions tried. The higher the concentration, the more harm will be done in the cell membrane. The information given demonstrated an ascent and fall circumstance in receptiveness as the concentration was raised. All in all, the higher the concentration of a solution, the higher the harm will be done on the cell membrane.


Request Removal

If you are the original author of this essay and no longer wish to have it published on the SpeedyPaper website, please click below to request its removal: