(Practical) Daphnia

Question 1

What is the independent variable?

Answer 1

caffeine concentration

Question 2

What is the dependent variable?

Answer 2

heart rate of Daphnia

Question 3

What is a control measure?

Answer 3

Using regular water

Question 4

What are some control variables?

Answer 4

Similar size Daphnia, counting for the same amount of time, time for Daphnia acclimatisation, volume of solutions, temperature

Question 5

What is the method for this experiment?

Answer 5

1. Remove Daphnia and place on the cavity slide
2. Remove pond water and replace with distilled water
3. Leave to acclimatise for 5 minutes and then count the heart rate under the microscope for 30 seconds. Counting can be done by dotting paper or using a slow motion camera which is more accurate
4. Multiply by 2 for bpm
5. Repeat this for 2 more Daphnia
6. Repeat this process again but use the caffeine solutions ranging from 0.1 to 0.5, repeating each 3 times.

Question 6

What are some possible evaluation issues?

Answer 6

Ensuring Daphnia are the same size
If left under the microscope too long the temperature will increase along with the heart rate
A high caffeine conc. will kill the Daphnia
Counting the heart beat can be innaccurate

Question 7

Why are Daphnia used?

Answer 7

Transparent simple organisms