State 2 factors the affect the permeability of cell membranes
- Temperature
- Concentration of solvents (ethanol)
How is beetroot used to measure the permeability of cell membranes?
The higher the permeability, the more red pigment that leaks out into the surrounding solution within a given time. A colorimeter can be used to determine the absorbance, hence concentration of pigment
Outline the procedure to investigate the effect of temperature on permeability of cell membrane
- Cut beetroot into 6 identical cubes with a scalpel
- Place each cube in a different test tube with equal volumes of distilled water
- Place each test tube into water baths ranging from 30-80c. Leave for 20 minutes
- Filter each solution out into a cuvette and measure the absorbance using a colorimeter
What are the safety hazards involved in testing the effect of ethanol concentration on membrane permeability?
- Ethanol is irritant and flammable, keep away from naked flames, wear eye protection
- Keep sharp scalpel away from fingers
- Handle hot liquid with care
What is the effect of temperature on membrane permeability?
Increasing temperature results in increase membrane permeability
What is the effect of ethanol concentration on membrane permeability?
Increasing ethanol concentration leads to increased permeability
Explain why its important to wash the beetroot discs
To wash off any pigment. To show that any pigment released is from ethanol
Suggest a suitable control variable
- Distilled water and two discs of beetroot
- To show that any pigment released was from the alcohol/ to compare it with the effects of alcohol
Explain why your results would have been different if you had used cooked beetroot.
- Heating/cooking would damage the (plasma) membranes;
- Valid explanation of damage e.g. disrupts phospholipid bilayer / denatures proteins in cell membrane;
- A lot of pigment released during cooking / less pigment present (in tissue);
Explain why a decrease in temperature of 5 °C would affect the results.
Less kinetic energy;
Molecules move slower;
Lower rate of diffusion;
Membranes less fluid;
Explain why you were instructed to shake the test tubes every minute
Increase the contact of all surfaces with the alcohol / prevent discs sticking together / maintain a diffusion gradient for the pigment
Explain why you were instructed to pour the alcohol immediately from the experimental test tube into a clean test tube
To limit the variation in time discs are in alcohol /make sure all the discs were in contact with alcohol for the same length of time / so no more pigment can diffuse out of the discs
