Effect of caffeine on the heart rate of Daphnia:
- Make up a range of caffeine solutions of different concentrations and a control.
- Transfer one Daphnia into the dimple on a cavity slide (a microscope slide with a rounded dip).
- Place the slide onto a light microscope and focus it on the beating heart of the Daphnia.
- Place a small drop of caffeine solution onto the slide.
- Count the number of heartbeats in 10 seconds and multiply this by 6 to get beats per minute.
- Repeat this 10 times using the same concentration but a different Daphnia each time.
- Repeat the experiment using all the caffeine solutions and the control.
- Draw a graph to compare the results.
It is unethical to cause distress to any of the Daphnia, you can reduce stress by making sure the light on the microscope isn’t left on too long so it doesn’t make them too hot.
Vitamin C practical:
- Measure out known concentrations of Vitamin C solution (e.g. 10mg/cm^3, 20mg/cm^3 etc.) Ideally there should be about 6
- Measure out the DCPIP of a known concentration and volume into a test tube.
- Slowly add the vitamin C solution drop by drop using a burette.
- Allow a set length of time after each drop to shake the tube.
- When the solution turns colourless record the volume of vitamin C solution added by reading the number off the burette.
- Repeat with the same vitamin C solution twice more and take an average, excluding any anomalies.
- Repeat the whole procedure with all the other concentrations.
- Make sure all other variables are controlled.
- Draw a calibration curve on a line graph.
Cell membrane permeability (temperature on beetroo
- Cut 5 equal sized pieces of beetroot and rinse them to remove any pigment released during the cutting.
- Place the 5 pieces in different test tubes each with 5cm^3 of water.
- Place each test tube in a water bath at different temperature, e.g. 10, 20, 30 degrees etc. for the same length of time.
- Remove the pieces of beetroot from the tube leaving just the coloured liquid.
- Use a colorimeter to find out how much pigment has been released.
The higher absorbance number > the more pigment released > so the higher the permeability of the membrane.