RP4: Investigation into the effect of a named variable on the permeability of cell-surface membranes

What is the semi-quantitative technique for this method? (9)

What is the quantitative technique for this method? (3)

Which variables should be controlled in an experiment using beetroot discs? (3)

- Source of plant tissue

- Length of time in solution

- Surface area to volume ratio of plant tissue

What is a limitation of using colour standards in an experiment? (2)

- Matching to colour standards is subjective.

- The colour obtained may not exactly match any of the colour standards

How does ethanol cause pigment to leak out of beetroot discs? (1)

Ethanol dissolves the phospholipids in the membrane, increasing the permeability of the membrane

Why does increasing the temperature to 30°C decrease the time for ethanol to turn red? (2)

- Increased temperature increases the kinetic energy of molecules.

- This increases the rate of diffusion of the pigment across the membrane.

Why should beetroot discs be washed in distilled water after cutting? (2)

- Cutting releases pigment from damaged cells.

- Washing ensures that any pigment in the distilled water comes only from the effect of the independent variable on membrane permeability.

Why were test tubes of distilled water left in the water bath for 5 minutes before adding beetroot? (1)

To allow the water to equilibrate (warm up to the required temperature)

Why did the student shake the test tubes every 5 minutes? (1)

To maintain the diffusion gradient for the pigment to pass out of the cells and into the distilled water

Why should fresh beetroot be used instead of cooked beetroot? (2)

- Cooking involves heating beetroot to high temperatures.

- This would denature membrane proteins, allowing pigment to leak out

What should a student do if they think one of their results is anomalous? (1)

Repeat the experiment in exactly the same way to check if the repeated result is similar

Why does absorbance plateau at temperatures above 60°C? (1)

No further diffusion occurs because the concentration of pigment inside and outside the cells is equal

Why does absorbance not have units? (1)

Absorbance is a ratio of the amount of light passing through a solution to the amount of light entering it