klb9
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My question is the same as the previous question I asked and wanted to know if that would change my answer

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.
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macpatgh-Sheldon
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Hi, (I am not sure what "previous Q" you mean)

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.
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