Anaerobic respiration is without the presence of oxygen, it produces lactic acid rather than carbon dioxide and water,
whereas in aerobic respiration oxygen acts as the final acceptor in oxidative phosphorylation, in anaerobic due to the
absence of oxygen the electron transport chain and Krebs cycle stop as they require oxygen so, this mean glycolysis is
the only source of ATP as oxygen is not required. For glycolysis to continue the reduced NAD made during glycolysis are
re-oxidised; no more than two ATP per glucose are produced at this stage but glycolysis is still occurring.
Respiration produces CO2 and H2O as by-products. When exercising muscles need to contract much more regularly thus
contraction requires more ATP which increases the rate of respiration. Increasing the rate of respiration will increase the
yield of the products of respiration (ATP, CO 2 & H2O). So, the relationship is directly proportional, as the time taken to
exercise/level of exertion increases, the amount of CO 2 produced increases. In neutral or basic solution, it is blue, and it
turns yellow in the presence of acid.
Our Hypothesis is “The volume of CO2 produced will increase with the level of exercise performed.”
EXPERIMENT: TIME TAKEN FOR BROMOTHYMOL BLUE TO CHANGE COLOUR (S)
1. Fill a 100 ml beaker with 40 ml of water and 10 ml bromothymol blue solution.
2. Place a straw into the solution in the beaker.
3. Start the timer and start breathing out through the straw into the bromothymol solution.
4. Continue to exhale through the straw, until the solution turns from blue to yellow-green. At this point stop the
timer. The problem here is deciding when the colour change has happened. Whatever point you decide to stop the
timer, you must do the same in the next part of the investigation.
5. Rinse the beaker out and refill with 40 ml of water and 10 ml bromothymol blue solution.
6. Jump up and down on the spot for one minute, so you are panting when you finish.
7. When you have finished exercising, start the timer and exhale into the solution through a straw and time how long it
takes for the solution to turn yellow-green.
8. Stop the timer when you observe the colour change and record the time. Try to ensure the colour is the same as
when you stopped in the control.
9. Record your results in an appropriate way and write a report on your investigation.
Repeating experiments produces more data so it is easier to see patterns and trends in your results, it improves the
reliability of your data so we can be surer our results are correct, and it allows you to identify mistakes or
anomalies/outliers in the data.
Each learner exercises for 12
minutes. There may be
differences in the time taken for
bromothymol blue to change
between participants; because
each participant may have
been a different size, their
training may be at a different
health/fitness level. There also
could have been a human error in exhaling into the solution or in starting/finishing the timer or inaccuracies in
measuring bromothymol blue. Anomalous results were taken out of the data analysis, and when we took it out the
trend was affected as before the standard deviation was much higher until the anomalous result was taken out in
participant 5 resting measurement 1 and was not calculated as part of the average. The graph shows that
The rate of carbon dioxide increasing as each participant is exercising more; they are respiring faster which is increasing
the amount of Carbon dioxide being produced, which shows in the water as the water changes the colour much quicker
from the presence of more carbon dioxide. the colour changes, the more CO2 is being produced as there are more
molecules present which makes the colour change to blue.
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