Effect of caffeine on daphnia heart rate

Question 1

What is the independent variable

Answer 1

Caffeine concentration

Question 2

What is the dependent variable

Answer 2

Heart rate

Question 3

What are the other variables that need to be controlled (5)

Answer 3

• Temperature
• Volume of solutions
• Stress of daphnia
• Size of daphnia
• Time of acclimatisation

Question 4

What equipment is used (7)

Answer 4

• Microscope
• Cavity slide
• Pipettes
• Stop clock
• Distilled water
• Test tubes
• Stop clock

Question 5

Give an outline of the method

Answer 5

Remove 1 Daphnia and place in cavity slide. Remove pond water and replace with distilled water. Leave for 5mins to acclimatise then observe & count heart rate under microscope for 30s, multiply number by 2 to calculate beats/min.
Repeat with 5 daphnia for each concentration

Question 6

What are the possible evaluation issues (5)

Answer 6

• Ensuring Daphnia were same size
• If left too long under microscope, temp increases (due to lamp) = increased heart rate
• Ensuring enough data is collected
• Too high concentration of caffeine kills Daphnia
• Counting of heart beat can be inaccurate