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AS Level Practical Questions
Daphnia Practical
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Cards (7)
Why is Daphnia selected as the organism in this practical?
They have
translucent
bodies so the
heart rate
can be more easily observed.
How does caffeine act in humans?
It is a stimulant that
increases
heart rate by increasing the release of
excitatory
neurotransmitters.
How is the control set up?
Replace caffeine solution with
distilled water
to measure the heart rate of the Daphnia without the effect of caffeine.
What steps should students take to ensure that the Daphnia are ethically treated?
• Minimise the amount of time exposed to
stressful
testing
conditions
•
Release
into a stream/pond after the practical
Why should a cover slip not be used when observing the organism?
To allow
oxygen
to reach the organism, preventing conditions from becoming
anoxic.
What is the purpose of placing cotton wool on the slide?
To
restrict
the
movement
of the organism so that it will be easier to count its
heart
rate.
Outline the procedure to this practical.
Dilute
the caffeine solution to produce several
concentrations.
Place some
cotton wool
on a cavity slide. Add one large water flea. Use filter paper to absorb excess water.
Use a dropping pipette to add a few drops of distilled water to the
slide.
Use a stopwatch to time a
minute
and record the number of heartbeats.
Repeat the experiment, replacing the distilled water with a
caffeine
solution.