core practical 5: temperature effect on membrane permeability

method

1. prepare 8 water baths pre-set to a range of temps eg. 0C - 70C

2. add 10cm3 of distilled water to eight test tubes/

3. place each tube in the corresponding water bath for 5 minutes.

4. check temp of each bath

5. cut eight beetroot cylinder using a cork borer - trim them all to the same length

6. wash the cylinders with water until the water runs clear and pat dry gently with a paper towel

7. add one beetroot cylinder to each of the eight test tubes and leave in the water bath for 15 minutes

8. shake the tubes once and remove cylinders

9. set colorimeter to green/blue filter and percentage transmission. callibrate colorimeter with a cuvette filled with distilled water.

10. transfer liquid from each test tube into a colorimeter cuvete and read the percentage transmission reading, record results in a table.

11. plot graph of transmission against temp.

what variables would be controlled and how would you control them

• volume of bathing water in each tube (10cm3)

• surface area and volume of the beetroot cylinders (dependent on size of cork borer; 1-2 cm in length)

• equilibriation time (5 mins)

• soaking time of cylinders (15 mins)

• volume of coloured liquid in cuvettes (15 mins)

• colorimeter filter used (green)

• part of the beetroot the core was taken from

• age, variety and storage time the beetroot was used

why were the test tubes placed in the water bath for 5 mins before the cylinders were added?

to allow the water to equilibriate to the desired temperature - accuracy

Why are the beetroot cylinders washed with distilled water and dried before the experiment?

to remove any excess pigment that has leaked from damaged cells during coring - the excess pigment would distort the percentage transmission readings leading to inaccurate results

What is your independent variable?

temperature

dependent variable

percentage transmission

Why is beetroot chosen as a suitable organism to investigate?

beetroot cells contain betalains pigment in their vacuoles which are a useful indicator of membrane fluidity as an increase in fluidity will cause the pigment to leak out of the cell.

Why is actual temperature recorded, rather than desired temperature?

As the water may not reach or maintain the exact desired temp

effect of temperature on percentage transmission between 0 - 70C

• percentage transmission decreases as temperature rises

• at around 40 - 60C percentage transmission decreases sharply

in terms of the membrane, explain how temp impacts membrane permeability

1. low temp → phospholids have little energy, packed closely together → betalain molecules too large to pass through

2. as temp increases, KE of phospholids increase → move more → more fluid → membrane more permeable → betalain molecules pass through membrane via diffusion → so percentage transmission decreases

3. After 40C, percentage transmission decreases as a fast rate → phospholid bilayer starts to break down

   • increasing KE of phospholids causes them to move far away from each other → loss of structural integrity

   • high temp denatures proteins in cell mambrane (can’t control cell exchange)

   • membrane permeability increases - more pigment leaks out

why do cuvettes need to be wiped for low temp solutions

condensation will cause lower transmission readings

hazards and how to control them

1. ethanol irritant + flammable → wear safety goggles, lab coat, no naked flames

2. scalpel sharp → keep away from fingers, take extra care when cutting, cut away from you

3. burn from hot liwuid → use tongs to remove test tubes from hot water bath