Practical Skills

Question 1

CP1 - Background Information

Answer 1

• Caffeine is a stimulant which increases heart rate by increasing release of excitatory neurotransmitters.
  -Daphnia are common water fleas, and are very abundant in nature so sampling some for laboratory practice will not have an impact on biodiversity. They are completely translucent, allowing their inner bodily processes to be observed, and are invertebrate - this means that they have a simple nervous system and therefore are unlikely to experience pain/discomfort during the investigation.

Question 2

CP1 - Equipment

Answer 2

Culture of Daphnia - investigative organism.
Container for ‘used’ Daphnia - Prevents the same Daphnia being used numerous times as the heart rate will be elevated.
Cavity slides - Used to immobolise and observe Daphnia, wash or replace each time to reduce residue.
Caffeine solution (1%) - Used to make serial dilutions.
Cotton wool - Used to immobolise Daphnia.
Dropping pipettes - Used to make serial dilutions and isolate Daphnia.
Distilled water - Used for serial dilutions, does not contain chlorine which kills Daphnia.
Test tubes - Make serial dilutions in.
Small measuring cylinder - Used for measurements when making serial dilutions.
Stop clock - Used to measure acclimatisation time and time intervals of counting heart rate.
Paper towels/filter paper - Used to remove any excess solution.
Microscope - Observe the Daphnia at magnification x100 - x400.
Pen and paper - Heart rate counting method.

Question 3

CP1 - Method

Answer 3

1) Dilute the caffeine solution with the appropriate volume of distilled water to produce several different concentrations.
2) Place some cotton wool (to restrict movement) on a cavity slide. Add one large water flea.
3) Use filter paper to absorb excess water around the flea.
4) Use a dropping pipette to add a few drops of distilled water to the slide. Do not use a coverslip to prevent conditions from becoming anoxic.
5) Use a stop clock to time a minute and record the number of heart beats.
6) Repeat the experiment, replacing the distilled water with the prepared caffeine solutions.

Question 4

CP1 - Risk Assessment

Answer 4

Biohazard - contamination - use disinfectant, wash hands with soap after handling Daphnia - seek assistance in an emergency.
Broken glass - cuts from sharp object - take care when handling glassware and keep it away from the edge of the desk - in an emergency elevate cuts, apply pressure, do not remove glass from wound, seek medical assistance.

Question 5

CP1 - Ethical Considerations

Answer 5

It is important to treat the Daphnia ethically during the experiment and release them back into a pond/stream afterwards.

Question 6

CP1 - Conclusion

Answer 6

Caffeine increases the heart rate of Daphnia by increasing the release of stimulatory neurotransmitters. As concentration of caffeine increases, heart rate also increases.