RP 4- investigating cell membrane permeability

Question 1

how can the permeability of a membrane be measured using beetroot cells? (3)

Answer 1

1) beetroot cells contain a purple ​pigment ​​called​ betalain.
2) ​​When the cell-surface membrane has a higher permeability, more pigment leaks out of cells
3) The permeability can therefore be measured by the ​amount of pigment leaked​​ from beetroot cells into an aqueous solution using a ​colorimeter​​.

Question 2

what is step 1 of this practical?

Answer 2

Cut beetroot into 6-10 ​identical cubes​​ using a scalpel

Question 3

what is step 2 of this practical?

Answer 3

Wipe/rinse to ​clean off any pigment​​ released as a result.

Question 4

what is step 3 of this practical? (2)

Answer 4

1) create a ​dilution series​​ of ethanol using distilled water
2) Ethanol concentrations should range from ​0-100%​​ ethanol.

Question 5

what is step 4 of this practical?

Answer 5

Leave the samples for ​20 minutes ​​- the pigment will leak out of the beetroot.

Question 6

what is step 5 of this practical?

Answer 6

Set the colorimeter to a ​blue filter​​ and​ zero​​ using a cuvette with ​distilled water​​

Question 7

what is step 6 of this practical?

Answer 7

place each sample into a cuvette using a pipette

Question 8

what is step 7 of this practical? (2)

Answer 8

1) Measure the ​absorbance​​ for each solution
2) A ​higher absorbance​​ indicates
higher pigment concentration​​, and hence a ​more permeable membrane​​.

Question 9

what are the conclusions from this experiment if done with ethanol? (3)

Answer 9

1) Ethanol causes the cell-surface membrane to ​rupture​​, releasing the betalain pigment from the cell
​2) Higher concentrations​​ of ethanol will cause ​more disruption​​ to the membrane and ​more gaps will form​​. 3) as concentration of ethanol ​increases​​, the permeability of the cell-surface membrane also increases​​

Question 10

what are the conclusions from this experiment if done by using temperature? (5)

Answer 10

1) As temperature increases, the permeability of the cell-surface membrane also ​increases​​
2) This is because the proteins in the membrane ​denature​​ as the heat damages the bonds​​ in their ​tertiary structure​​
3) This ​creates gaps​​ in the membrane, so it is easier for molecules to pass through it.
4) At low temperatures, phospholipids have ​little energy​​ and are ​packed closely together​​ to make the membrane​ rigid​​. This causes a ​decrease​​ in permeability and restricts molecules from crossing the membrane.
5) At ​very low ​​temperatures, ​ice crystals​​ can form which ​pierce the cell membrane and ​increase​​ the permeability.