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Biology investigation - investigating the relationship between the breathing rate and the carbon dioxide concentration of exhaled air

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James Fung 18thJanuary,2002 Biology investigation - investigating the relationship between the breathing rate and the carbon dioxide concentration of exhaled air Result: Breathing rate (Breathes per minutes) A B C D E Resting 12 14 8 12 15 2 minutes exercise 25 20 18 22 25 3 minutes rest 14 10 15 19 16 6 minutes rest 13 5 9 17 15 Carbon dioxide concentration (Carbon dioxide %) A B C D E Resting 19% 3.9% 8.1% 40.8% 6% 2 minutes exercise 20% 3.2% 8.3% 100% 31% 3 minutes rest 2.5% 13.9% 4.8% 47.3% 12% 6 minutes rest 6.3% 2.1% 3.5% 77.3% 9% Fig.2 Analysis: For those 5 sets of data I have got, I have drawn them up on Fig.1. Then I have chosen the one from person E to analyse further, which gives Fig.2. There are some chemoreceptors, which are situated in the medulla of the brain, the arch of the aorta and in the wall of the carotid arteries. And they are stimulated when there is an increase in carbon dioxide level inside our body. ...read more.


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. 2) 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. 3) 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. ...read more.


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: 1) 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 2) Sample collecting --- not to collect gas that I breathe out first because there is no gas exchange to these gas 3) 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 4) The depth of breathing --- try to ask everyone to take a depth breath before blowing out the gas collected 5) Potassium hydroxide used --- try not to use cold potassium hydroxide The end ...read more.

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