# AS BIOLOGY UNIT 3 PRACTICALS

EXPERIMENT 1

Effect of caffeine on Daphnia heart rate

Remove 1 daphnia using a pipette and place on a cavity slide.
Remove excess pond water by dabbing the daphnia and the slide GENTLY with a paper towel.
Drop a few drops of distilled water on the daphnia and leave for five mins to acclimatize.
Observe and count heart rate for 30 seconds and multiply by 2 to calculate beats/min. (Or simply count heart rate for one minute).
Repeat the experiment at least three times and take average.
Repeat again using five different concentrations of caffeine.
Repeat each concentration three times, and take average.

Independent:
caffeine concentration.

Dependent:
heart rate of daphnia.

Controlled variables:
Temperature
Volume of solutions
Stress of daphnia
Size of daphnia
Time of acclimatization

(Turn off the light microscope after you're done counting heart beat to minimize the heat effect on the daphnia as heat will increase its heart rate)
(Too high caffeine concentrations kills daphnia)

EXPERIMENT 2

Measuring the content of vitamin C in fruit juice

Pipette 1cm^3 of blue DCPIP into a test tube.
Using a burette, add 1% vitamin C solution drop by drop.
Shake tube gently after each drop.
Continue to do this until the blue colour of the DCPIP disappears.
Record the volume of solution needed to decolourise the DCPIP.
Repeat two more times and take average. This is your control.
Repeat the experiment again with different fruit juices.
Record your findings in a table.

Independent: fruit juice.

Dependent: volume of juice required to decolourise 1cm^3 of DCPIP

Controlled variables:
Temperature.
Concentration of DCPIP solution.
Shake each tube same number of times.
Same end point colour.

CALCULATION:
Mass of vitamin C to decolourise 1cm^3 DCPIP = mass in sample x volume of sample

EXPERIMENT 3

The effect of temperature on cell membranes

Using a cork borer and a knife, cut pieces of beetroot into 1 cm length cylinders.
Place in distilled water overnight to remove excess pigment released from the cutting.
wash and gently blot dry using a paper towel.
Place 8 boiling tubes of distilled water into 8 different water baths of different temperatures.
Once at temperature, add a piece of beetroot each and leave for 30 mins.
Remove beet roots and shake tubes to disperse dye.
Set colorimeter to % absorbance on blue/green filter.
Calibrate using distilled water in a cuvette first then add 2cm^3 of beetroot solution from the first temperature to a new cuvette.
Place into colorimeter to read % transmission.
Repeat for all other pieces.

Independent: temperature of water.

Dependent: % transmission of light through resulting solution. (Or permeability of membranes)

Controlled variables:
Volume of distilled water.
Time left in water.
Size of beetroot piece.

CALCULATIONS:
% transmission =
100 - % absorbance.

(If you use %absorbance instead of transmission)

EXPERIMENT 4

The effect of changing enzyme concentration on rate of reaction

Make up different concentrations of

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# AS BIOLOGY UNIT 3 PRACTICALS

EXPERIMENT 1

Effect of caffeine on Daphnia heart rate

Remove 1 daphnia using a pipette and place on a cavity slide.
Remove excess pond water by dabbing the daphnia and the slide GENTLY with a paper towel.
Drop a few drops of distilled water on the daphnia and leave for five mins to acclimatize.
Observe and count heart rate for 30 seconds and multiply by 2 to calculate beats/min. (Or simply count heart rate for one minute).
Repeat the experiment at least three times and take average.
Repeat again using five different concentrations of caffeine.
Repeat each concentration three times, and take average.

Independent:
caffeine concentration.

Dependent:
heart rate of daphnia.

Controlled variables:
Temperature
Volume of solutions
Stress of daphnia
Size of daphnia
Time of acclimatization

(Turn off the light microscope after you're done counting heart beat to minimize the heat effect on the daphnia as heat will increase its heart rate)
(Too high caffeine concentrations kills daphnia)

EXPERIMENT 2

Measuring the content of vitamin C in fruit juice

Pipette 1cm^3 of blue DCPIP into a test tube.
Using a burette, add 1% vitamin C solution drop by drop.
Shake tube gently after each drop.
Continue to do this until the blue colour of the DCPIP disappears.
Record the volume of solution needed to decolourise the DCPIP.
Repeat two more times and take average. This is your control.
Repeat the experiment again with different fruit juices.
Record your findings in a table.

Independent: fruit juice.

Dependent: volume of juice required to decolourise 1cm^3 of DCPIP

Controlled variables:
Temperature.
Concentration of DCPIP solution.
Shake each tube same number of times.
Same end point colour.

CALCULATION:
Mass of vitamin C to decolourise 1cm^3 DCPIP = mass in sample x volume of sample

EXPERIMENT 3

The effect of temperature on cell membranes

Using a cork borer and a knife, cut pieces of beetroot into 1 cm length cylinders.
Place in distilled water overnight to remove excess pigment released from the cutting.
wash and gently blot dry using a paper towel.
Place 8 boiling tubes of distilled water into 8 different water baths of different temperatures.
Once at temperature, add a piece of beetroot each and leave for 30 mins.
Remove beet roots and shake tubes to disperse dye.
Set colorimeter to % absorbance on blue/green filter.
Calibrate using distilled water in a cuvette first then add 2cm^3 of beetroot solution from the first temperature to a new cuvette.
Place into colorimeter to read % transmission.
Repeat for all other pieces.

Independent: temperature of water.

Dependent: % transmission of light through resulting solution. (Or permeability of membranes)

Controlled variables:
Volume of distilled water.
Time left in water.
Size of beetroot piece.

CALCULATIONS:
% transmission =
100 - % absorbance.

(If you use %absorbance instead of transmission)

EXPERIMENT 4

The effect of changing enzyme concentration on rate of reaction

Make up different concentrations of