Biology RP4

Factors affecting membrane permeability

Give three factors that could be the independent variable of the investigation.

• Temperature.

• pH.

• Solvent concentration.

What equipment do you need when investigating the effect of temperature on membrane permeability?

• Scalpel.

• Cutting board.

• Cork borer.

• Ruler

• Tongs.

• Distilled water.

• Boiling tubes.

• Boiling tube rack.

• Colorimeter.

• Cuvettes.

• Timer.

• Water baths of different temperatures.

• Paper towels.

What is a quantitative way in which you can measure membrane permeability?

Measure absorbance/transmission with a colorimeter.

What is a semi-quantitative way you can measure membrane permeability?

Compare solutions to premade dilutions of pigment extract.

Talk me through the process of preparing beetroot samples for five different temperatures.

1) Using a cork borer, cut five cylinders out of the same beetroot.

2) Using a scalpel and ruler, cut all beetroot cylinders to the same length.

3) Blot the beetroot samples dry with paper towels.

Why do you blot the beetroot samples dry?

So that any pigment that affects the concentration of the distilled water has come from the effect of temperature on membrane permeability, not cutting beetroot.

Why do you leave the boiling tubes with distilled water in the temperature baths for five minutes?

To allow the water to equilibrate before adding the beetroot.

How long should you leave the beetroot samples in the boiling tubes?

For 20 minutes.

How do you choose which filter to set on the colorimeter?

Choose the filter that is complementary to the colour of the pigment (opposite the colour of the pigment on the colour wheel).

What does higher absorbance indicate about pigment concentration and therefore membrane permeability?

Higher absorbance means higher pigment concentration meaning greater membrane permeability.

Give three hazards in this investigation, the risks associated with them, and how to avoid them.

• Scalpel, cuts, cut away from fingers.

• Broken glass, cuts, handle glassware carefully and keep away from edges.

• Hot liquids, scalding, use tongs to remove boiling tubes from water baths and wear eye protection.

Why does increasing temperature increase membrane permeability?

Higher temperatures break bonds in the tertiary structure of proteins in membranes, creating more gaps in the membrane and making it easier for larger molecules to cross the membrane.

True or false? Extremely low temperatures can increase membrane permeability.

True.

How do extremely low temperatures increase membrane permeability?

Ice crystals form which pierce the cell membrane and increase it’s permeability.

Why do you shake the test tubes containing beetroot and distilled water every five minutes?

To maintain a diffusion gradient that allows pigment to continue diffusing out of the beetroot cells and into the water.