- Keeping the same Daphnia for each experiment.
- Using the same piece of equipment for recording the same for each experiment.
- Using the same person to do the recording.
- Use the same measurements then it will be fair.
SAFETY:
The equipment should be used safely so that we can get the right observations. If something went wrong because the experiment wasn't safe then the observations that we would get would be wrong and also may affect the results. The amount of the caffeine that we use should all be to the correct measurement as then the results would be fair. Safety that can be used is that all bags are to be put under the table except the bags would have to be tucked in properly so that no one can trip over the bag. Also this is important as then you won't throw caffeine over someone else or kill any daphnia's.
APPARATUS:
Culture of Daphnia
Cavity slides and cover slips;
Dropping pipettes
Distilled water
Cotton wool
Caffeine tablets
Stop clock
Paper towel/ filter paper
Microscope
Lamp
HYPOTHESIS:
I believe that an increase in caffeine concentration in the surrounding water on the daphnia results in an increase in heart rate.
This is known because caffeine is a stimulant, which has the effect, among other things, of increasing the heart rate of any living organism, which consumes or absorbs it. Caffeine causes increased amounts of stimulatory neurotransmitters to be released. At high levels of consumption, caffeine has been linked to raise blood pressure and raised heart rate.
A high dosage of caffeine results in an increased neurone firing in the brain. The pituitary glad sees all the activity and thinks some sort of emergency must be occurring, therefore releasing hormones that tell the adrenal glands to produce adrenaline. Adrenaline is the 'fight or flight' hormone and has a number of effects on your body. Some of the effects happen to be an in heart BPM (beats per minute), which is an increase in heart rate, and an increase in blood pressure.
Just like in a human heart, a Daphnia's heart will beat faster when receiving a dose of caffeine.
METHOD:
A few strands of cotton wool were placed on a cavity slide (helps restrict the movement of the Daphnia). Using a pipette, one large water flea was transferred to the cavity slide. Before doing so, the water around the Daphnia was removed using a paper towel. A few drops of distilled water were added to the cavity slide containing the Daphnia. A cavity slide filled with iced water was placed under a different slide and was sealed by a cover slip (this will act as a heat sink). This slide was then placed below the slide containing the Daphnia, and was inserted under a microscope, and a lamp, which was at a reasonable distance from the microscope, was used to provide light. The built-in microscope light was not used as this would give temperature to the Daphnia and water, which could affect the results. The Daphnia was then viewed under low power, focussing on its heart, which was able to be seen through its translucent body.
A stop clock was then used to record the number of heart beats per 15 seconds. This made it easier as it was only monitored for 15 seconds rather than 60. A pen was the tapped on a piece of paper to represent the number of heart beats during the time period, and this was counted up at the end of the time period and the number was multiplied by 4 (4 x 15sec = 60sec/1min) to obtain the BPM.
This experiment, using the caffeine solution, was repeated a further 2 times with other Daphnia, and fresh slides and cover slips, using the same procedures as above..
In each of the 3 experiments, however, different concentrations of caffeine solution were used. In the first, 2 drops were used, in the second; 4 drops were used, and in the third and final, 6 drops were used.
RESULTS:
CONCLUSION:
The results obtained clearly show that the higher the concentration of the caffeine, higher the heart rate. This proves the original prediction. As was mentioned before, the reason for this is most likely be due to the fact that caffeine is a stimulant and an increase in its concentration results in a higher heart rate.
The daphnia is unique in that it absorbs the chemicals that are present in the water surrounding it without selection. Therefore, with low concentrations such as those used in these experiments, it is likely that the daphnia will absorb most, if not all, of the caffeine present in the surrounding water.
The reason why the heart rate of the daphnia increases when it is given a dose of caffeine is the same reason as for a human's rise in heart rate due to its intake. Caffeine belongs to a group of compounds called methylxanthines and among its effects are two that result in a higher heart rate. It blocks a receptor, called an adenosine receptor, on the surface of the heart muscle, which produces an enzyme called adenosine. One of the effects of adenosine, and the one that is relevant here, is that it slows down the heart rate. Indeed, in humans, adenosine results in sleepiness, one of the causes being a slower heart rate. Therefore, if this receptor, which regulates the heart rate by controlling the level of adenosine, is blocked and thus the level of this enzyme is lowered then the heart rate rises.
One of the important reasons why such a noticeable change in heart rate takes place due to an increased concentration of chemicals surrounding the daphnia is its physical makeup. As was mentioned previously, the daphnia is unique in that it absorbs any chemicals in the water surrounding it straight into its body. Therefore any chemical that has a physiological effect affects the daphnia almost instantaneously. For this reason, the daphnia is actually used as an indicator for toxicity of chemicals. Its heart rate is measured to find out how toxic a liquid is.
EVALUATION:
There are many factors, which affect the results. The most obvious factor with the method used to measure the daphnia's heart rate. A daphnia's heart rate can rise to a very high rate, especially when using a stimulant such as caffeine, and thus it can be very difficult to measure using a ticker timer or even dotting on a paper. This is due to the restraints of the human reflexes; they are simply not fast enough in some cases.
Another major factor is that it is feasible that a larger daphnia would not be as greatly affected by a certain concentration of caffeine as a smaller daphnia. This is because a larger daphnia would have a more diluted level of caffeine within its system.
Other factors, which could affect the heart rate are, the temperature of water surrounding daphnia, the concentration of chemicals in the surrounding water (could reduce caffeine intake), amount of water surrounding daphnia, the concentration of oxygen in the surrounding water, the drops of iced water into the slide (could affect the temperature). The concentration of other gases in the surrounding water such as carbon dioxide could also affect the temperature as it can limit the amount of oxygen in the surroundings.
The caffeine solution used could not have been fully mixed in with the water; therefore the concentration taken could not have been what it was actually planned to be.
