A level BiologyWatch
Daphnia can be used to investigate the effect of chemicals such as caffeine on heart rate by placing it in a drop of water under a microscope and counting the heart beat.
State two variables that you would need to control for a valid investigation into the effect of caffeine on the heart rate of the Daphnia. Describe how to control these variables.
1. Temperature: you need to keep a steady temp - we know that enzymes work faster at a higher temp - also that our own (human) heart rate is faster when we have a pyrexia (fever) by 10 beats/min for every 1C above the normal 37C.
As we are using a drop of water ONLY, keep the room temp steady e.g. at 25C with a thermostat.
2. pH: keep the pH steady; different physiological processes work differently in low or high pH conditions.
Use litmus paper(??)
3. Supply of O2
4. Supply of fatty acids - these are the main substrate of human myocardial cells - I have no idea about Daphnia's heart.