Daphnia Practical (1)

Question 1

Why are daphnia suitable organisms for investigating effect of chemicals on heart rate?

Answer 1

• Transparent, heart can be seen so heart rate can be counted
• Simple nervous system, daphnia can’t feel pain
• Absorb chemicals from surrounding quickly, high surface area to volume ratio.

Question 2

State and justify suitable control for investigation:

Answer 2

Pond water, used to record daphnia’s normal heart rate, with absence of chemicals

Question 3

Variables that should be controlled and how is it done?

Answer 3

.Temperature, heat shield
.Volume of caffeine solution, use pipette to measure, 2 cm3
.Age and species of daphnia, hatch from eggs at same time
.Concentration of caffeine, place one caffeine tablet in 10cm3 of water

Question 4

Devise this procedure:

Answer 4

1)Collect daphnia with pipette from beaker with pond water
2)Put cotton wool on cavity slide to stop it moving about
3)Place daphnia in slide and observe it with light microscope
4)Use filter paper to absorb water around daphnia then use pipette to drop certain volume of distilled water
5)Count the heart rate in a minute with a pencil, each beat make a dot as their heart beats at a fast rate
6)Remove water with filter paper and add solution with 0.25% concentration, measure heart rate, then do it with 0.5% and 1% concentration, repeat 3 times for each concentration to get average
7)Control the temperature, size/age/species and sex of daphnia, volume of solution

Question 5

Safety measures:

Answer 5

.Daphnia could carry infections from the water they live in, wash hands before and after practical
.Use of glassware