Daphnia heart rate

Question 1

What’s the independent varaible?

Answer 1

caffeine concentration

Question 2

What is the dependent variable?

Answer 2

heart rate of daphnia

Question 3

Equipment needed:

Answer 3

micoroscope, cavity slide, stop clock, pipette,

Question 4

What are other variables to control? (4)

Answer 4

• temperature
• volume of solutions
• stress of daphnia
• time of acclimatisation

Question 5

What is the method? (9)

Answer 5

1. remove daphnia and place on a cavity slide
2. remove pond water (with tissue) and replace with distilled water, place cottton woll in the cavity so daphnia cannot move
3. leave for 5 mins to accliamatise
4. Observe and count daphnia’s heart rate under miscroscope for 30s
5. multiply by 2 to get beats per min
6. repeat with two more daphnia
7. repeat again with small concentrations of caffeine solution in place of distilled water
8. carry out for 5 concentrations of caffeine solution.
9. repeat to get a mean

Question 6

Possible evaluation issues.

Answer 6

• ensuring daphnia are same size, gender, age
• if left too long under microscope temperature increases due to lamp - temp increase = increased heart rate
• ensuring enough data is collected
• dont kill the daphnia
• counting can be innacurate
• ethics