The regulation of breathing is an example of homeostasis. When the concentration of carbon dioxide rises this stimulates an increase in breathing rate, which in turn reduces the concentration of carbon dioxide, leading to a decrease in breathing rate.
Fig.2 shows a trend that as the carbon dioxide concentration increases from 6% to 31%, the breathing rate increases from 15 to 25 breaths per minutes. This trend is expected and fully support the biological theory described above.
i.e. Increases in carbon dioxide concentration level Detected by chemoreceptors
Increased breathing rate and depth Return to resting level
Conclusion and evaluation:
There are several errors, which could have made the results inaccurate. And they are:
- The effect of heat when handling the equipment --- when people collected the air they have blown out into a test tube. But because we were holding the test tube with our hand, the warmth from our hand might have made the concentration of carbon dioxide to reduce.
- Sample collecting --- when collecting the expired air, we were not meant to collect the air, which first came out, because this air is from the trachea, so there wouldn’t be any gas exchange happened to this air. If the gas collected hasn’t be diffused in the lung, the concentration of carbon dioxide would almost be the same as the air we breathed in. Results, which are affected, would possibly be A & C. This is because the carbon dioxide concentrations of person A & C at resting and after 2 minutes exercise were nearly the same.
- Time --- there was water inside the tube when we carried out the second part of the experiment, which was to find out the carbon dioxide concentration. This was due to those test tubes have been left for few days after the air has been collected because we didn’t have enough time to finish it in the same day. And because carbon dioxide dissolves in water, so this could have affected the results. Normally, the concentration of carbon dioxide should be highest in 2 minutes exercise. And it should be higher at 3 minutes rest after exercise than 6 minutes. Results, which have been affected, would be from person A, B &D. Because the carbon dioxide concentration of person A & D at 3 minutes rest is lower than at 6 minutes rest after exercise. And for the concentration of carbon dioxide of person B at resting than after 2 minutes exercise.
--- we didn’t have enough time to repeat the experiment.
- The depth of breathing --- because the depths of breathing differ from people to people, so this may also be a factor, which have affected the results. Just like the result from person B, the carbon dioxide concentration was generally lower when comparing with the other.
- Potassium hydroxide used --- person D might have used some cold potassium hydroxide, which lead to the 100% of carbon dioxide of expired air. E.g. person D generally had a higher carbon dioxide concentration than the others.
Because of the possible errors that I have mentioned above, there are a few anomalous results. Like results from person A, B & D didn’t follow the rule that as the concentration of carbon dioxide goes up, the breathing rate goes up. Besides, person D’s result is awkward compare with the others because the concentration of carbon dioxide at different times are extremely high especially the one after 2 minutes exercise, she had 100% carbon dioxide concentration.
If I have a chance to do this experiment again, I would do it better by improving the possible errors I have mentioned. Improvements to the respective errors like:
- The effect of heat when handling the equipment --- in order to reduce the warmth from the hand into the tube, I would hold the tube with a test tube holder instead of my hand
- Sample collecting --- not to collect gas that I breathe out first because there is no gas exchange to these gas
- Time --- try to finish the whole experiment in the same laboratory with almost the same temperature in one day and repeat the experiment for a few times to get an average result
- The depth of breathing --- try to ask everyone to take a depth breath before blowing out the gas collected
- Potassium hydroxide used --- try not to use cold potassium hydroxide
The end