Practicals

Question 1

Describe the procedure to find the effect of temperature on membrane permeability.

Answer 1

1. Label 5 test tubes each with temps from 20 to 60 degrees
2. Add 10cm3 distilled water to each tube with a measuring cylinder
3. Place each tube in corresponding water bath for 5 minutes so the water can equilibrate to the correct temp
4. Record their actual temp with thermometer and leave tubes in the water baths
5. Trim 10 beetroot cylinders into 30mm with scalpel and ruler on a white tile
6. Rinse cylinders under a running tap and pat dry with paper towel
7. Add 2 cylinders to each tube and leave for 15 minutes
8. Label 5 cuvettes each with temps from 20 to 60 degrees
9. Remove the tubes from water bath, carefully swirl once and use forceps to remove cylinders
10. Throw cylinders into waste receptacle
11. Pour remaining liquid into each corresponding cuvette
12. Use colorimeter to measure absorption and percentage transmission and record in a table

Question 2

How does temperature affect membrane permeability?

Answer 2

• At increasing temperatures, phospholipids in the plasma membranes gain more kinetic energy, making membrane more fluid and increasing permeability because they move further away from each other
• This allows more spaces for substances like pigments to diffuse through
• Proteins in membrane denature, disrupting membrane structure and increasing permeability
• Damages cell surface membrane, becoming freely permeable

Question 3

How do solvents affect membrane permeability?

Answer 3

Solvents like ethanol increase membrane permeability, because
- Phospholipids in the plasma membrane will dissolve in alcohol, causing the plasma membrane to become more fluid and permeable
- Higher concentration of solvent –> PPLs break down at a faster rate because the higher conc dissolves them more and the plasma membranes are damaged
- More spaces for substances to diffuse through

Question 4

What are 4 limitations of the procedure for investigating the effect of temperature on membrane permeability?

Answer 4

1. When beetroot cylinders are removed with forceps they are squeezed slightly so extra pigment is released, therefore increasing the absorption reading and reducing validity
2. Limited temperature range of only 5 temps differing by 10 degrees. Hard to identify when the fluidity and permeability of membrane changes and whether there are anomalies
3. No repeats so can’t calculate the mean or identify anomalies
4. Concentrations of betalain in each beetroot cylinder are inconsistent, some may contain higher concs than others so release more betalain even at lower temps