These are the notes for BIOLOGY A LEVEL UNIT 3. It contains the summary of all the practical tests you must have conducted in class, including the independent/ dependent and controlled variables as appropriate. And the method of conducting the experiments as expected in the examinations.
,I. The effect of caffeine on heart rate
Independent Variable – Caffeine Concentration
Dependant Variable – Heart Rate (bpm)
Controlled Variables –
Temperature
Some feature of Daphnia (age / size /sex);
Pre-treatment / acclimatisation / recovery time
Q. Ethical implications of using Daphnia
1. Simple nervous system / invertebrate so reduced awareness of pain
2. Transparent so no need for dissection
3. Abundant in nature so no threat to it or its dependent species (food chains)
4. Bred for fish food will thus die anyway
5. May be clones therefore there is no loss of genetic variation
6. Animal welfare argument e.g. cannot give consent / may feel pain
7. Possibility that the Daphnia could die
Q. Give two reasons why Daphnia is a suitable organism for investigating
the effect of chemicals on heart rate.
1. You can see the {heart / internal organs}
2. Daphnia {are simple organisms / have less developed nervous system / can’t
feel pain}
3. There are fewer ethical concerns because it is an invertebrate
4. Easily obtainable / cheap / abundant
5. They can absorb chemicals from the surrounding solution quickly
6. Idea that Daphnia {well studied / model organism}
7. Daphnia are easy to manipulate
Q. Suggest how the student should position the Daphnia and the
thermometer in order to obtain valid results.
1. Daphnia positioned so heart visible
2. Idea of immobilising Daphnia
3. Thermometer (bulb) submerged in pond water
4. Idea that thermometer positioned close to Daphnia
, Q. Describe how the student should take counts of the Daphnia’s heart
rate at 20°C to obtain reliable results.
1. Repeats
2. Idea of system of counting in set time e.g. beats per 20sec
Q. Suggest two reasons why the student decided not to carry out the
investigation at high temperatures.
1. Hard to count at higher temperatures because heart rate too fast
2. Harm to Daphnia
3. Idea of being unethical
Method:
Q. Describe an experiment that the student could perform, using Daphnia, to
confirm that herbal tea has the lowest caffeine content.
Q. Describe how this investigation could be
carried out using Daphnia instead of
chicken embryos
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