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Biology > Topic 1: Vitamin C core practical > Flashcards

Topic 1: Vitamin C core practical Flashcards

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1
Q

What are free radicals? (1 point)

How do they form? (1 point)

A
  1. Free radicals are an atom or molecule which has a FREE UNPAIRED ELECTRON, so are UNSTABLE.
  2. Free radicals FORM DURING METABOLIC REACTIONS in the body and increase the risk of a person developing CVD.
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2
Q

Free radicals are _____ ________ and can damage cell components (proteins, enzymes, lipids or DNA) by _______ _______ __________.

They have been implicated in the development of cancer, heart disease and premature ageing.

A

highly reactive

stealing their electrons

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3
Q

What does Vitamin C do to the body? (2 points)

A

Vitamin C in fruit is an antioxidant.

  1. Wen we eat fruit the vitamin C PROVIDES ELECTRONS to neutralise FREE RADICALS, SO THEY DO NOT CAUSE {CELL/DNA} DAMAGE
  2. This reduces the risk of a person developing CVD.
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4
Q

What is DCPIP (dichlorophenolindophenol)? (1 point)

What are its two forms? (2 points)

How to you change it from its coloured form to its colourless/pink form? (1 point)

A
  1. It is an indicator which exists in two forms.
  2. oxidised DCPIP is BLUE
  3. reduced DCPIP is {PINK/COLOURLESS}
  4. To change DCPIP from the blue oxidised form to the colourless reduced form, ELECTRONS AND HYDROGEN IONS ARE NEEDED
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5
Q

Vitamin C provides the _________ and _________ ____ to reduce and decolourise DCPIP (change the oxidised blue DCPIP into reduced colourless DCPIP)

The ____ vitamin C present in the fruit juice (when it has a higher concentration), the ____ electrons and hydrogen ions will be provided, so the _______ the volume of juice needed to reduce the DCPIP and change it from blue to colourless

A

electrons

hydrogen ions

more

more

lower

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6
Q

What is the independent variable? (1 point)

How do you vary it? (1 point)

A
  1. Type of fruit juice
  2. Use different types of fruit juice e.g. orange, grapefruit
    (use pale coloured juices so the colour change is more visible)
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7
Q

What could be used as control? (1 point)

Justify the control (1 point)

What does it prove? (2 things)

A
  1. distilled water with 0% vitamin C (1 point)
  2. The control is used for COMPARISON

Proves that:

  1. when there is no vitamin C present to provide electrons, the DCPIP cannot turn colourless on its own
  2. there is nothing in distilled water that can provide electrons to DCPIP
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8
Q

What is the dependent variable? (1 point)

How will you measure it? (2 points)

A
  1. The vitamin C concentration.
  2. TITRATE JUICE INTO DCPIP USING A BURETTE
  3. We will measure the volume of juice needed to change DCPIP from blue to colourless, then use this to determine vitamin C concentration.
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9
Q

Controlled variables are for ________.

A

validity

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10
Q

what are the controlled organism variables?

2 controlled variables

A
  1. Same source of juice - {freshly squeezed/from concentrate juice}
  2. Same storage time and temperature of juice before the investigation
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11
Q

what are the controlled environmental variables?

1 controlled variable

A
  1. Same TEMPERATURE OF JUICE AND DCPIP – take out of fridge same time before testing each juice
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12
Q

What are the controlled procedural variables?

2 controlled variables

A
  1. SAME VOLUME OF DCPIP – 5cm^3 with graduated pipette

2. SAME CONCENTRATION OF DCPIP - 0.05% – from same stock solution

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13
Q

How many repeats? (1 point)

Why? (3 points)

A
  1. 5 repeats for each type of juice
  2. to identify anomalies - anomalies should be repeated and then discard the original anomaly
  3. Repeat until 3 concordant results are obtained – then calculate a mean
  4. Improves RELIABILITY
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14
Q

What to do to get validity?

4 things

A
  1. 5 values for independent variable (if not comparing)
  2. More vitamin C concentrations on calibration curve
  3. Controlled variables must be controlled
  4. Use a control (if appropriate)
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15
Q

What is the risk in the practical? (1 risk)

How can you minimise the risk? (1 way)

A
  1. Risk – DCPIP may irritate and damage eyes

1. Minimising risk – wear safety goggles

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16
Q

Key Summary:

Vitamin C) Describe the practical method (7 steps

A
  1. Extract the juice from the fruit
  2. Place juice in a BURETTE and the DCPIP in a FLASK under the burette
  3. Titrate juice into 5cm3 of dark oxidised DCPIP
  4. Until colour change - from blue to {colourless/pink} and RECORD THE VOLUME OF THE JUICE needed to decolourise the DCPIP
  5. Repeat 5 more times, obtain 3 concordant results and calculate mean volume of juice – improves reliability
  6. Use a calibration (standard) curve constructed from known vitamin C concentrations to determine
    vitamin C concentration of juice
  7. Name 2 controlled variables eg. volume and concentration of DCPIP, temperature of juice
17
Q

How should you write your conclusion for this practical? (2 points)
(Comparison between vitamin C concentration in orange juice and grapefruit juice)

A
  1. “The concentration of vitamin C in orange juice is ………% and the concentration of vitamin C in grapefruit juice is ………%.”
  2. “Therefore ……… juice has a higher concentration of vitamin C.”
18
Q

List the experimental design question checklist

A
  1. IV - Independent variable + how it is varied for VALIDITY
  2. C - Control (if appropriate) + why it is needed
  3. DV - Dependent variable + how it is measured
  4. M - Method detail e.g. DCPIP, blue to colourless, calibration curve
  5. CVO/E - Controlled variables for VALIDITY (organism + environment + procedure)
  6. R - Repeats for RELIABILITY+ why they are needed
  7. S - Safety (paired points)
19
Q

Extract the juice from the fruit

What is the purpose of this step? (1 point)

A
  1. Juice can be titrated, fruit cannot
20
Q

Titrate juice into DCPIP

What is the purpose of this step? (1 point)

A
  1. Vitamin C provides electrons which reduce DCPIP
21
Q

Look for colour change e.g. from blue to {colourless/pink} and record volume of juice used

What is the purpose of this step? (1 point)

A
  1. Gives volume of juice used to decolourise DCPIP, so that this volume can be read off a standard curve
22
Q

Repeat 5 more times and calculate mean volume of juice used

What is the purpose of this step? (1 point)

A
  1. Improves reliability and allows anomalies to be identified
23
Q

Use a {calibration/standard} curve to determine vitamin C concentration

What is the justification of this step? (1 point)

A
  1. Calibration curve has been constructed using solutions with known vitamin C concentration
24
Q

Name 2 controlled variables e.g. volume of DCPIP, temperature

What is the purpose of this step? (1 point)

A
  1. So that we know the differences in vitamin C concentration are due to type of juice, not another variable

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