Activity 1.23: Does Caffeine affect heart rate?

What treatments are you investigating in this experiment? Control (distilled water) Vs 0.2% caffeine solution

Prior to examining the Daphnia under the microscope you should allow time (e.g. 3-5 minutes) for the Daphnia to acclimatise to the solution in which you have placed them.

1. Place a few strands of cotton wool on a cavity slide to restrict the movement of the Daphnia. Using a pipette transfer one large Daphnia to the cavity slide, keeping plenty of water surrounding the flea. Do NOT use a cover slip! Using the microscope on the lowest magnification, focus on the Daphnias heart, which can be see through its translucent body.2. Use a pencil and paper (or whiteboard and pen) and a stop clock to record the number of heartbeats in 30 seconds.3. Repeat the process a minimum of two more times and calculate the mean. Remember that if you identify any outliers as you are doing your repeats you should discount the outlier and repeat again.4. Repeat steps 1-3 for a different treatment (i.e. control vs caffeine OR five different concentrations of caffeine) using a different Daphnia. Work in pairs using the blind technique. Topic One Core Practical: Effect of caffeine on Daphnia HypothesisH: Daphnia heart rates will be higher in the 0.2% caffeine solution compared with the control as the caffeine acts as a stimulant, causing stimulatory neurotransmitters to be released.NH: Daphnia heart rates will be unaffected by the higher concentration of caffeine in the 0.2% solution

VariablesIndependent Variable Caffeine concentrationDependent Variable Daphnia heart rateControl Variables Temperature Volume of solution Stress of daphnia Time of acclimatisation Control VariableHow it will be controlled?Why must it be controlled?

Temperature

Temperature will be controlled by carrying out each test in the same room and keeping the door shut to reduce risk of temperature change between experiments.

Volume of solutionVolume of caffeine solution will be controlled by taking each beaker of solution from the same 2.0% mix so that there is no variation between experiments.Amount of caffeine in the daphnias blood will affect its heart rate, meaning that variation of caffeine solutions will skew results.

Stress of daphnia

Stress of daphnia will be controlled by only using non-impregnated daphnia that are all the same size. Their time under the microscope must also be the same throughout the tests so as to keep stress levels caused by the light of the microscope the same.Increased stress levels will increase the heart rate of the daphnia, meaning that a variation in stress of each daphnia could skew results.

Time of acclimatisation

Time of acclimatisation will be controlled by timing the amount of time each daphnia spends acclimatising to the solution/control; each daphnia will spend 5 minutes in their respective solution/control.Amount of caffeine in the daphnias blood will affect its heart rate and the time taken to acclimatise to the caffeine solution will affect the amount f caffeine in the daphnias blood. This means that a variation in acclimatisation time will skew results.

Why are we using Daphnia in this experiment?

EthicsWhen using living organisms in experiments it is important to be aware of the ethical implications. For example, what precautions did you take to ensure their safety? Is it appropriate to use the animals in scientific research? Etc.This webpage should help your understanding of ethics. Have a quick look to check your understanding: http://www.bbc.co.uk/ethics/introduction/intro_1.shtml 1. What is ethics?

2. Think of at least three ethical arguments which are either for or against the use of Daphnia in this practical.ArgumentEthical PointFurther explanation this point/argument

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3. Ethical Question: What is the utilitarian argument for using living organisms in scientific experiments? Do you think this ethical argument supports the use of Daphnia in this particular experiment?

Now complete the following and add to your core practical report Results Table (including repeat columns, mean and standard deviation). Graph of results (Including error bars representing standard deviation) Discussion (Refer to the Practical Support 1 document Planning and writing up an experiment which is available under the tab skills support on SNABonline.com to help you complete this section) Evaluation (Discuss the possible limitations of this technique and how they could be overcome in this section, not in the discussion) References (Any references e.g. journals etc., cited in your discussion should be referenced in FULL in this section. You are expected to add such research in to your report particularly as it is a skill required for your AS coursework. There is a document dedicated to referencing on the Moodle AS Biology page accessible via the SMRT website).

Super Sauce Question (This should be added in between the evaluation and the references section) A)Caffeine affects neurotransmitter levels in the brain. Daphnia have no brain, so how did the caffeine produce its effect?B) Can we extrapolate our findings on Daphnia directly to humans? Give a reason for your answer.