Topic 1

Question 1

Why are daphnia used to investigate heart rate?

Answer 1

They are transparent so their hearts can be seen and heart rate monitored

Question 2

Explain how to measure the effect of caffeine on the heart rate of daphnia 9

Answer 2

• Make up a range of caffeine solutions of different concentrations using serial dilution
• Use a control solution with no caffeine
• Transfer one Daphina into a dimple on a cavity slide
• Use a pipette to place a few drops of caffeine solution onto Daphnia
• Wait for 5 minutes for all caffeine to be absorbed
• Place onto stage of light microscope and adjust focus to see Daphnia beating heart
• Count number of heartbeats in 20 seconds and x3 for bpm
• Repeat 10 times using same caffeine conc but different Daphnia
• Repeat using other concentrations and control

Question 3

What factors should be kept the same in the Daphnia experiment?

Answer 3

• Temperature

- Volume of caffeine solution

Question 4

What are the ethical disadvantages in using invertebrates? 2

Answer 4

• Can’t give consent

- Extreme conditions could cause distress

Question 5

What are the ethical advantages in using invertebrates? 3

Answer 5

• Less sophisticated nervous system than vertebrates
• Feel less pain
• More distantly related to humans

Question 6

What dye is used to investigate concentration of vitamin C in food?

Answer 6

DCPIP

Question 7

What colour change does DCPIP undergo when added to vitamin C?

Answer 7

Changes from blue to colourless

Question 8

Explain how to investigate concentration of Vitamin C 8

Answer 8

• Make up 6 vitamin C solutions of different known concentrations
• Use a measuring cylinder to measure out set volume of DCPIP at set concentration
• Add a Vitamin C solution to DCPIP drop by drop with pipette
• Gently shake for set amount of time using stopwatch
• When solution is colourless, record the volume of vitamin C solution added
• Repeat twice with same solution, and whole method with each concentration
• Draw a calibration curve of the result, by plotting graph of concentration of Vitamin C vs volume in drops
• With unknown solution compare volume to calibration curve to find concentration