Core Practicals

Question 1

Core practical 1 - investigating heart rate

Answer 1

1. Dilute the ca eine solution with distilled water to produce several di erent concentrations.
2. Place some cotton wool (to restrict movement) on a cavity slide. Add one large water flea.
3. Use filter paper to absorb the water around the flea.
4. Then use a dropping pipette to add a few drops of distilled water to the slide (don’t use a coverslip to
   prevent conditions from becoming anoxic)
5. Use a stopwatch to time a minute and record the number of heartbeats.
6. Repeat the experiment, replacing the distilled water with a ca eine solution.

Question 2

Core practical 3: investigating permeability of membranes

Answer 2

1. Use scalpel to carefully cut five equal sized pieces of beetroot
2. Rinse the pieces to remove any pigment released during cutting.
3. Use a measuring cylinder or pipette to measure 5 cm° of water into five di erent test tubes.
4. Place the test tubes into water baths at di erent temperatures, e.g. 10 °C, 20 °C, 30 °C, 40 °C, 50 °C. for
   around 5 minutes to allow the water to reach the desired temperature.
5. Place the five pieces of beetroot into the five di erent test tubes, for the same length of time (measured
   using a stopwatch).
6. Remove the pieces of beetroot from the tubes, leaving just the coloured liquid.
7. Next, use a pipette to transfer a sample of the liquid from the first of your beetroot test tubes to a clean
   cuvette - it should be about three quarters full
8. Put the cuvette in the colorimeter and record the absorbance of the coloured solution.
9. Repeat steps 2-3 for the liquids in the remaining four test tubes (using a clean pipette and cuvette each
   time).
10. The higher the absorbance reading, the less light is passing through the solution meaning more pigment
    has been released, so the higher the permeability of the membrane.

Question 3

CORE PRACTICAL 3 - INVESTIGATE MEMBRANE PERMEABILITY

Answer 3

Use scalpel to carefully cut five equal sized pieces of beetroot
2. Rinse the pieces to remove any pigment released during cutting.
3. Use a measuring cylinder or pipette to measure 5 cm° of water into five di erent test tubes.
4. Place the test tubes into water baths at di erent temperatures, e.g. 10 °C, 20 °C, 30 °C, 40 °C, 50 °C. for
around 5 minutes to allow the water to reach the desired temperature.
5. Place the five pieces of beetroot into the five di erent test tubes, for the same length of time (measured
using a stopwatch).
6. Remove the pieces of beetroot from the tubes, leaving just the coloured liquid.
7. Next, use a pipette to transfer a sample of the liquid from the first of your beetroot test tubes to a clean
cuvette - it should be about three quarters full
8. Put the cuvette in the colorimeter and record the absorbance of the coloured solution.
9. Repeat steps 2-3 for the liquids in the remaining four test tubes (using a clean pipette and cuvette each
time).
10. The higher the absorbance reading, the less light is passing through the solution meaning more pigment
has been released, so the higher the permeability of the membrane.

Question 4

CORE PRACTICAL 2 - INVESTIGATE VITAMIN C CONTENT IN FOOD

Answer 4

1. Make up several vitamin C solutions of di erent, known concentrations (about six di erent solutions)
2. Use a measuring cylinder to measure out a set volume of DCPIP (at a set concentration) into a test tube
3. Add one of the vitamin C solutions to the DCPIP, drop by drop, using a pipette.
4. When solution turns colourless, record the volume (no. of drops) of vitamin C solution that has been added.
5. Repeat the experiment twice more, with the same solution, and take an average of the three readings.
6. Make sure you keep all the other variables constant during the experiment, e.g. temperature.
7. Repeat the above procedure with each solution.
8. Use the results to draw a curve of best fit, showing volume of vitamin C solution against its concentration -
   this is the calibration curve