Topic 1 Core Practicals

Question 1

Vitamin C

Answer 1

An antioxidant common in many foods such as citrus fruits. Important in neutralising free radicals which can damage cells.

Question 2

Vitamin C content practical

Answer 2

• antioxidants are reducing agents (lose electrons)
• many substances change colour when reduced (therefore called redox dyes)
• DCPIP blue -> colourless

Question 3

DCPIP

Answer 3

A blue dye in its non-reduced form. It goes colourless when in the presence of vitamin C as it gains electrons

Question 4

Daphnia CP steps

Answer 4

• place cotton wool on cavity slide
• use pipette to transfer one daphnia onto cavity slide
• remove excess water using filter paper
• add two drops of distilled water
• set up microscope, making sure heart is in clear view
• use stopwatch to record bpm
• tap pencil on paper to record each heartbeat
• repeat, using other water fleas, clean slides and different concentrations of caffeine solution instead of water

Question 5

Ethical issues of daphnia CP

Answer 5

• simple nervous system - may not feel pain in the same way
• no need for dissection
• abundant in nature
• bred for fish food
• no loss of genetic variation
• cannot give consent
• cannot express pain

Question 6

Why use daphnia?

Answer 6

• abundant
• easy and cheap to obtain
• transparent, so heart can be seen
• simple nervous system (less of an ethical issue than humans)

Question 7

limitation of daphnia

Answer 7

they are not human, so conclusions drawn should be considered carefully when extended to humans

Question 8

ensuring a successful experiment (daphnia)

Answer 8

• immobilise Daphnia (cotton wool)
• control variables
• accurate measurement of heart rate (e.g., dots in S shape, repeatedly press calculator button)

Question 9

control variables (daphnia)

Answer 9

• water temperature (thermometer to monitor, as water temp. is difficult to maintain)
• age, sex and size of Daphnia
• aspects of pretreatment (e.g., type of water, length of time out of natural habitat)

Question 10

CP2 method (vitamin C)

Answer 10

1. Prepare 1% solution of vitamin C and 4 different fruit juices
2. Pipette 1cm^3 of 1% DCPIP solution into a test tube
3. Record the start volume of 1% vitamin C solution in a burette
4. Add 1% vitamin C solution drop by drop to the DCPIP solution, swirling tube gently after each drop
5. Continue to add drops of vitamin C until blue DCPIP has turned colourless
6. Record end volume and subtract start volume from end volume to obtain volume of 1% vitamin C solution used
7. Repeat for fruit juices in place of 1% vitamin C solution

Question 11

CP2 results

Answer 11

Volume of vitamin C solution required to decolourise DCPIP should decrease as the concentration of vitamin C solution increases