Hypothesis
I think that the amount of caffeine in the blood will determine the heart rate of the daphnia. It will be directly proportional to each other i.e. the increase of the % of caffeine will also increase the heart rate of the daphnia.
Safety
- Make sure you concentrate the solution so that the daphnia does not get too much of it and die.
- Take care with the glassware make sure that they do not break.
- The microscopes are fragile and the light bulbs can get hot so be careful of that.
Apparatus
• Culture of Daphnia (water fleas)
• Cavity slides and cover slips
• Dropping pipettes
• Distilled water
• Caffeine tablets
• Cotton wool
• Standard glassware (beakers, measuring cylinders etc)
• Stop watch
• Paper towels or filter paper
• Microscope.
Procedure
1. The beating heart of a water flea can be seen through its translucent body,
by placing the flea in a few drops of water in a cavity slide. A cover slip
helps stop the water evaporating.
2. Place a few strands of cotton wool on a cavity slide; this will help restrict
the movement of the water flea.
3.Using a pipette, transfer one large water flea to a cavity slide. Remove the water from around the water flea using filter paper, then add one or two drops of distilled water.
4. Use as much water as you can and do not use a cover slip.
5. Together these precautions will help maintain sufficient oxygen supply to the flea. A cavity slide filled with iced water and placed under the slide will act as a heat sink.
6. View the water flea under low power. Focus on its heart which can be seen
through it translucent body.
7. Use a stop watch to record the number of heart beats per minute.
8. Tap a pencil on a piece of paper and count up the pencil marks at the end of the time period.
9. Record the heart rate at intervals of two minutes over a 10 minute period. It is a good idea to do a ‘blind’ study to avoid bias in the results.
10. In order to make the best assumptions of the results the reader of the amount of heart beats there are and the concentration of the solution should be uninformed.
11.Repeat the procedure using other water fleas from the culture solution and fresh, clean slides and cover slips. Replace the water with caffeine solution. Repeat the procedure using several different concentrations of caffeine.
Results
Evaluation
When looking at the results that I have obtained I can see that when adding more caffeine concentration to the water flea, the heart will also increase and there fore the prediction that it will be directly proportional is correct. For example when the control had only a heart beat of only 160BPM the daphnia with 0.1% concentration of caffeine had a heartbeat of 296. this is almost 1.8 times more heartbeats than a regular one.
When doing this experiment in particular we have to look at some issues that are ethical and by this I mean when testing fleas for the use of science. I had decided that it was ok that we used these daphnia for the sake of science as it may help us in the future. Another way of looking at this is to say that if everyone was to do this experiment with daphnia then the amount of daphnia left will be little and this will then cause a major disruption in the food chain and may soon have some deadly effects. When finished with the daphnia we could out them back in their natural habitat and then everything will be alright. The ethical issues will be mainly brought up when we use a higher concentration that will kill the daphnia this is why we have to make the solution dilute first.
In every experiment, only the reliable and accurate results are useful. The more of these we do and taking an average we will be able to get a fairly good result and because we used the class results I believe that this is going to be a highly reliable experiment. This may not be the case when we get errors from places and so to get an even better result we should look at the results and take out some of the anomalous results.
An example of an anomalous result is that I had got a lower heart beat rate when using a 0.00001% concentration of caffeine and if my prediction is to be right this cannot be. I then have to blame this on systematic errors. As I have mentioned before we may have to see different daphnia for different concentration this by itself will produce a very high % error as we can only assume that the heart beat for every daphnia will be the same but in reality it is not. This can also be put down to just clumsy result taking. As we had left this one till last it is clear that we could not really be bothered to be as accurate as we had been with the other ones. Another example is that the room may have been at different temperatures at different times and therefore this is an error as we know that the temperature will also make a difference to the heart beat.
