Topic 2 Core Practicals

Question 1

CP3 - membrane permeability method

Answer 1

1. Place eight labelled boiling tubes, each with 5cm^3 distilled water, into water baths with different temperatures. Leave for 5 mins
2. Cut cylindrical 1cm samples from beetroot using cork borer
3. Rinse tubes with distilled water and roll twice over paper towel to remove excess dye
4. Place beetroot into boiling tubes. Leave for 20 mins in water baths
5. Decant liquid into second boiling tube. Shake solution to disperse dye.
6. Turn on colorimeter and set to read percentage absorbance
7. Set filter dial to blue
8. Measure 2cm^3 distilled water into cuvette using pipette. Place cuvette in colorimeter
9. Adjust colorimeter to read 0 absorbance for clear water
10. Place 2cm^3 dye solution into cuvette and take reading for absorbency. Repeat for all temperatures.

Question 2

CP3 theory

Answer 2

• fluid mosaic model suggests temperature might affect cell membranes
• as temperature increases, absorbance increases, meaning permeability increases
• as temperature increases, phospholipids will become more fluid, allowing molecules to leak from the cell
• phospholipids move more due to more KE, which means they are less tightly packed
• proteins in the membrane also denature as heat damages tertiary structure bonds, creating gaps in the membrane

Question 3

CP3 temperatures used

Answer 3

0, 10, 20, 30, 40, 50, 60, 70˚C

Question 4

CP4 - enzyme concentrations and enzyme activity method

Answer 4

• measure 1cm^3 of protein solution into a cuvette
• measure 1cm^3 of protease solution into the cuvette
• mix and put cuvette into colorimeter
• measure absorbance at suitable time intervals (e.g. every 30s) for 5 mins
• discard contents of cuvette and rinse with distilled water
• plot graph of absorbance against time and calculate initial rate (gradient)
• repeat using a range of different enzyme concentrations

Question 5

CP4 theory

Answer 5

• as the milk protein casein is digested, the white, opaque milk colour becomes more pale and translucent, eventually turning colourless
• more light passes through the transparent and lighter solutions, meaning absorbance is lower
• the higher the trypsin concentration, the faster the rate of reaction, the lower the initial absorbance reading will be, as paler solutions absorb less light