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Effect of caffeine on daphnia heart rate
Independent : caffeine concentration
Dependent : heart rate of daphnia
Controlled variables:
volume of solutions,
stress of Daphnia,
size of Daphnia,…read more

Slide 3

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Method and outcome
1. Remove 1 daphnia and place in cavity slide
2. Remove pond water and replace with
distilled water
3. Leave for 5 mins to acclimatise then observe
and count heart rate under microscope for
4. Multiply by 2 to calculate beats/mins
5. Repeat with 2 more daphnia. Repeat again
but this time with a small concentration of
caffeine in the distilled water.
6. Carry out for 5 concentrations of caffeine =
3 repeats at 3 concentrations.
OUTCOME: as caffeine concentration
increased heart rate increased…read more

Slide 4

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Possible evaluation issues
Ensuring daphnia were the same
If daphnia left too long
underneath microscope
temperature increases so heart
rate increases
Too high concentration of
caffeine kills daphnia
Counting heart beat can be
inaccurate…read more

Slide 5

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Measuring content if vitamin c in fruit
Independent : fruit juice
Dependent: volume of juice required to
decolourise 1cm3 of DCPIP
Variables to control
Concentration of DCPIP solution
Shake each tube same number of times
Same end point colour…read more

Slide 6

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Method and outcome
1. Pipette 1cm3 blue DCPIP into test tube
2. Add 1% vitamin c solution drop by drop
3. Shake gently after each drop
4. Continue until DCPIP is colourless
5. Repeat further 2 times to get an average
6. Repeat with different fruit juices
Calculations: 1cm3 of 1% vitamin c solutions contains 10mg
vitamin c therefore mass in 1cm3 = 10mg x volume of 1%
vitamin c to decolourise 1cm3 of DCPIP
Mass in sample = mass of vitamin c to decolourise 1cm3 DCPIP
/ volume of sample required to decolourise 1cm3 DCPIP…read more

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