Use cotton wool to stop the Daphnia from moving about to much, this makes it easier to keep the daphnia to see and count the heart beats.
Use pond water do that they are in there natural environment rather than plain water.
After the experiment they are put in a fish take to be fed to the fish, they aren’t wasted.
Variables:
Independent variable: Caffeine, this is the quantity that I am controlling, I am going to control the amount of caffeine out onto the daphnia.
Dependant variable: heart rate, this is the quantity under investigation, I am going to count the heart rate of the daphnia whilst in water and then in a caffeine solution and compare them.
Fixed variables: Same animal, have to use the same species and either the same animal for the experiment or if the animal dies the if you swap animals you have to make sure they are similar sizes, otherwise its is an unreliable test.
Reliability and validity:
I don’t think that my results were very valid or reliable. It was very hard to count the heart beats because the heart was eating to fast to count. You might not always get the right beat for the heart either. Therefore I could have counted the heart beats wrong. One way that you could solve this problem is to use strobe lighting and set it so that it looked like the heart wasn’t moving at all. You would then know that the heart was beating at the same speed as the strobe lighting. This would mean that the heart beat count was more reliable and valid.
Errors
There is a possibility of random error when you are counting the heart beats. You cant control how much you go over counting the heart beats by. A systematic error could be if the concentration of the caffeine was wrong. If it was stronger then the heart rate would increase whereas if it was weaker then it was meant to be then the heart beat would be slower.
Results
Trends
If there is caffeine solution surrounding the daphnia, it reacts very fast on the body and increases the hart rate dramatically. This is because the caffeine solution reacts as a stimulant increasing the heart rate making the blood move around the body faster to get to the working muscles faster.
Validity and precision:
I think that my results were precise because they were all very close to each other. I had no anomalous results. My non caffeine results had a range of 14 and my caffeine results had a range of 78 which is larger. This is because it was harder to count the heart beats when the heart was beating faster.
Conclusion
I think that the caffeine makes the heart of the daphnia beat faster this mean that more blood is being pumped from the heart around the body. For further investigation we could try the experiment on larger animals such as dogs or humans. Or you could try the experiment on the same animal but with different concentrations of caffeine. If I was to experiment the investigation further I would find an animal which it is easier to measure the heart rate on such a human where you can use a machine.