To make the investigation a fair test I will use the same daphnia all the way through so that the size and the consumption of alcohol is the same in one daphnia. If I was to use different daphnia then I wouldn’t be getting accurate results because one daphnia may be bigger than another and one may be an adult while another is a child. Also if a daphnia which has been gradually added to more alcohol then its heart rate will hopefully decrease gradually instead of using different daphnia’s who’s hearts rates will be all different. Also to make my experiment a fair test I will use a very accurate syringe, which specifically can hold only one millilitre of a liquid. This way I will be able to measure the exact amounts of distilled water and alcohol.
By putting the distilled water and alcohol into a mixing beaker this will be a lot more accurate then adding them separately onto a slide. It will be very hard to measure a precise amount because the slide an only hold a certain amount of liquid before it overflows.
Here is a diagram for all the equipment I will need to use:-
Prediction
The Nervous System is needed to control our body. It tells organs how to work together so that our bodies work efficiently. We have two main ways of transferring information from one part of our body to another. It can do this by sending electrical signals along nerves. Another way to communicate our body is by sending chemical messages through our blood. Our brains and spinal cord control our nervous system. This is our Central Nervous System. It received information from all parts in the body, and sends messages to other body parts telling them what to do. The nerves carry information around your body. The cells, which make up the brain, spinal cord and nerves are called neurones or nerve cells.
The axon carries electrical impulses; it can be up to several metres long as well. The axon can carry a message very easily, transferring it a very long way in a second. Dendrites are found around the cell body. They make contact with other nerve cells around them to receive information. Information is given to the Central Nervous System by receptors, which are in all parts of your body, they are sensitive to certain aspects of the environment, like the retina in your eye is sensitive to light. Receptors work by transferring energy into electrical energy. This is used to send an impulse along the nerve fibres to your brain or spinal cord. Other receptors are touch receptors in your hands are sensitive to movement, and smell receptors are sensitive to chemical energy. In Daphnia they have got a nervous system. They need nervous impulses sent through their body to be able to communicate their organs to make their body efficient but it is in a very simple form.
Stimulus
Central Nervous System
A neurone sends nerve impulses in only one direction only. The nerve impulses arrive from one neurone to another by chemical neurotransmitters, which are in between the small gaps of the two nerve cells. The transmitter allows electrical impulses to pass onto the other neurone dendrites. This is then taken to the Central Nervous System, to the brain then back to the Central Nervous System and taken through the effectors, which result in a muscle moving to move your body. The Neurotransmitter is affected by the bulk of information that needs to be transferred or by drugs. This too happened in Daphnia but its Nervous System is not as complicated as ours.
Caffeine is a stimulant, it speeds up to demand for neurotransmitters which are supplied so that the electrical impulses can be passed from one neurone to another much quicker. By doing this it quickens a persons reactions by making them more alert and aware of what is going on.
Alcohol is a depressant as is the opposite to a stimulant. When alcohol is taken into your body it decreases the number of neurotransmitters that are produced so that electrical impulses are not carried to other neurones as quick as someone not taking drugs. That’s why our actions slow down. This process is the same for daphnia’s but simpler. Alcohol changed a person’s judgment and prevents them from doing certain skills like driving a car correctly and safely. Alcohol causes vasco-dilation in your skin, which makes a person feel really warm when actually their body temperature drops an awful lot.
Stimulants increase the number of neurotransmitters made so that the electrical impulses will be able to cross to the next neurone much quicker. Once the transmitter has delivered the impulse it breaks down. When a person takes a stimulant it also affects other parts of the body and your organs. It results in quickened reactions and makes a person more alert. Also, because they are more alert and ready for action, they need to produce more energy to supply the body cells. This mans that glucose is released from the liver and more oxygen is taken into the lungs because there has been an increase in your the heart rate.
For depressants this process is the opposite. They stop the release of neurotransmitters and stop the neurotransmitters acting on the second neurone. When an electrical impulse is taken to the ending of the first neurone, the impulse has to wait to be taken across to the second neurone by the neurotransmitters. This means that they have to wait so our body’s action are slowed down. Because they have slowed down reactions, less energy is needed because we are doing less activity. Less glucose and less oxygen are required so the heart rate decreases. We look at daphnia’s heart rate because it is very easy to find and we can count the number of beats per minute.
I think that adding more alcohol to the daphnia’s environment, it will decrease their heart rate. I think that this will happen because of the research I did in my background information. Because the number of neurotransmitters being released decreases, this will result in slower reactions, less energy will be needed to supply the cells which results in a slower breathing rate. Because there is slower breathing, oxygen isn’t taken into the lings as quick so the heart doesn’t have to pump the blood as fast to supply the cells with oxygen. This results in a lowered heart rate.
Because it may be hard to take an accurate reading for the daphnia’s heart rate I will do the experiment twice, this way I can check to see if the information I have gathered is correct. By doing the experiment twice it will also help if in one set of results show odd results.
Conclusion
From doing this experiments and repeating it again to make sure I had more accurate results, I can see that as the daphnia is put into a more concentrated amount of the alcohol its heart rate lowered. On the graph the two separate results are not exact but I can see that both times the daphnia’s heart rate showed the same pattern. As the concentration of alcohol increased, the daphnia’s heart rate decreased. In the first experiment there was one odd result when I was testing the daphnia’s heart rate in 0.2 ml of alcohol. This is because when I put the daphnia into the 0.2 ml of alcohol and 0.8 ml of distilled water the daphnia died straight away, so I had to use another daphnia. The reason why the heart rate increased was because this daphnia was a bigger size compared to the one before, which meant it was able to tolerate the alcohol concentration better and wasn’t affected by the alcohol as much. This meant its heart rate didn’t slow down as much as the first daphnia.
The pattern that is formed on the graph is a falling curve. Because at the beginning of the experiment there was more distilled water then there was alcohol the daphnia wasn’t affected. As more alcohol was added it’s decreased the daphnia’s heart rate so the plots on the graph decreased and formed a curve. From doing this experiment, the trends of the graph tell me that if I was to add the daphnia into 0.5 ml of alcohol and 0.5 ml of distilled water then gradually increase the amount of distilled water it is put into the graph would show a steady increase because the daphnia’s heart rate would speed up.
On the graph it shows that the more the alcohol is increased the slower the heart rate becomes. This is because the daphnia has a Nervous system, which can be affected by the usage of drugs. In their bodies they have nerve cells or neurone which are able to send electrical impulses from different organs in the body, also they can send information by carrying chemical messages in the blood so they are able to work efficiently. The way that these electrical impulses are co-ordinated is by the Central Nervous System. The ‘CNS’ for short is made up of our brain and spinal cord. The nerves, which carry the information around the body, have an axon, which carried the electrical impulses. Receptors are responsible to give the Central Nervous System the messages so that they can act and send an electrical impulse back through the body via a motor neurone and to an effecter.
A neurone sends nerve impulses in one direction only. The nerve impulses arrive from one neurone to another by chemical neurotransmitters, which are in between the small gaps of the two nerve cells. The transmitter allows electrical impulses to pass onto the other neurones dendrites. This is then taken to the Central Nervous System, to the brain then back to the Central Nervous System and taken through the effectors. The Neurotransmitter is affected by how much information needs to be transferred or by drugs.
As we added more alcohol to the daphnia’s environment it decreased the number of neurotransmitters that are released which causes electrical impulses not to carried from one neurone to another as quickly. The neurotransmitters act as a ‘ride’ for the electrical impulses, which means the impulses, can only get across if there are enough neurotransmitters to take them. If someone is under the influence of drugs this will automatically slow down their reactions, their heart rate and the ability to understand things as they would when they are sober. This is why the daphnia’s heart decreased as more concentration was added to the distilled water they were living in.
Because a daphnia’s skin (exoskeletons) is clear, we can watch their hearts beating without cutting them open. This lets us see how different substances can affect their heart rate. In daphnia’s their nerve impulses are controlled by pacemaker neurons, which are in a group of nerve cells called the cardiac ganglion. These impulses are then sent to the follower neurons, which take signals to the cardiac muscles to make, the heart beat. All of their cells are protein, which is hidden in the daphnia’s cell membrane. These are called ‘receptor proteins’. These receptors let the daphnia’s cells communicate between themselves. Nerves can receive communication from cells far away or from cells which are really close. The cells that are far away release hormones which travel to the target nerve’s ‘hormone receptors’. Once these hormones attatch them selves to the receptors it makes a change in the nerves. Some of the hormones are able to increase the heart rate and some of them are able to decrease the heart rate too.
Also sometimes, receptors can accidently attatch themselves to neurotransmitters which increase the amount of messages that are carried through their body. Plus they can also cause the nerve to stop taking messages as quickly, so the nerve activity decreases. That’s why when the daphnia is put into alcohol, the nerve fibres attatch them selves to it which causes a slowed down nerve activity in its body, which causes the heart rate to drop.
Evaluation
I think that my experiment did prove what I wanted to find out. When I was planning the experiment I made it as fairer a test that I could. I used accurate syringes which were able to hold 1 millilitre of liquids. This was because I neded to measure a precise amount of alcohol so that when I added it to the daphnia’s environment it would be able to tell me clearly how much alcohol would affect the daphnia’s heart rate. Because I was adding 0.1 ml of alcohol and 0.9 ml of distilled water into a beaker I neded that syringe because other wise it wouldn’t of been as easy measuring it out in a measuring beaker or another piece of equipment. To have a good reading of the daphnia’s heart rate, when I put it into a new solution I waited for three minutes so that the daphnia calmed down and so it wasn’t moving around as much because this would of made it really difficult for me to count its heart rate. When I counted its heart rate I only did it for 30 seconds. This was because it was very hard to keep counting the heart beat because it was very fast but also the daphnia kept on moving around. Once I had the number of times it beated I multiplied it by two so that I could measure it in beats per minute.
The only anomalies I had in my results was in the first experiment when the daphnia died. The second daphnia I used had a higher heart rate and I think that the reading was higher when it was put into 0.1ml of alcohol and 0.9 ml of water because of the size of the daphnia. Because it was bigger I don’t think it affected it as much as the first one.
I did the experiment twice because I knew that there would be a good chance of the daphnia dying when I was reading its heart rate and this may of gave me unaccurate results. Also if I had two sets of results I would be able to compare them and look for patterns between the two. On the graph I did a line of best fit for the two experiments so that you can see the general trend of the experiment. As the alcohol concentration increased, the daphnia’s heart rate decreased.
When I measured the heart rate it wasn’t as accurate as it should have been because it beating many times in 30 seconds. Also I had to change the daphnia in experiment one because it died, so this daphnia had a higher heart beat compared to the original one. I think if I was to do the experiment again I would count the number of time the heart beat for 15 seconds then multiplied the answer by four. This way I would not of miscounted and I would get much more accurate results.
If I was to repeat the experiment again I would first have a better lamp or put the microscope in the window so that I could see the daphnia more clearly. When I first looked at the daphnia I couldn’t find its heart rate but I think this was because I couldn’t see the slide very well. Another thing I would do is when I put the daphnia into it’s new environment I would leave it to rest for five minutes, this way the affects of the alcohol on the daphnia would have time to work and I would get a better reading of how the alcohol decreases its heart rate. Another way I could improve my experiment was when I was timing how many time the daphnia’s heart beated I could use another two people and we could count for ten seconds each then add our scores together and multiply by two. This would make it more accurate aswell.
