AS Biology SNAB Practicals

AS Biology SNAB Practicals

CORE BIOLOGY PRACTICALS
You will need to know these practicals as the exam board may ask you questions based on them. Below is a summary of each one.
Name of practical and
independent & dependent
variables
Effect of caffeine on Daphnia
heart rate
Independent: caffeine
concentration
Dependent: heart rate of
Daphnia
Measuring the content of
Vitamin C in fruit juice
Independent: fruit juice
Dependent: volume of juice
required to decolourise 1cm3 of
DCPIP

The effect of temperature on cell
membranes
Independent: temperature of
water
Dependent: % transmission of
light through resulting solution

The effect of changing enzyme
concentration on rate of
reaction.
Independent: concentration of
enzyme
dependent: time taken for
enzyme to break down substrate

Other variables to
be controlled

Other equipment

Method and outcome

Temperature
Volume of solutions
Stress of Daphnia
Size of Daphnia
Time of
acclimatisation

Microscope, counter,
cavity slide, dropping
pipettes, stop clock,
distilled water, test
tubes, stop clock

Method: Remove 1 Daphnia and place in cavity slide. Remove pond water and
replace with distilled water. Leave for 5mins to acclimatise then observe & count
heart rate under microscope for 30s, multiply number by 2 to calculate beats/min.
Repeat with 2 more Daphnia. Repeat again, this time with small concentration of
caffeine solution in place of distilled water. Carry out for 5 concentrations of caffeine
= 3 repeats at 3 concentrations.
Outcome: as caffeine concentration increased, heart rate increased

Ensuring Daphnia were same size
If left too long under microscope, temp
increases (due to lamp) = increased heart rate
Ensuring enough data is collected
Too high concentration of caffeine kills
Daphnia
Counting of heart beat can be inaccurate

Temperature
Concentration of
DCPIP solution (1%)
Shake each tube
same number of
times
Same end point
colour. i.e. until the
blue colour of...

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