Q1. An experiment was carried out to investigate the effect of different duration of activity on the percentage of carbon dioxide in exhaled air.
In this experiment, a student rests for 0 minute and his exhaled air is collected to analyse the carbon dioxide content in the air sample.
The experiment is repeated with the same student after running on the spot for 1 minute, 2 minutes and 3 minutes.
The exhaled air is collected immediately after each activity. In this experiment, a J-tube is used to analyse the carbon dioxide content in the exhaled air. Potassium hydroxide solution is used to absorb carbon dioxide in exhaled air.
Sample answers
(a) Record the lengths of air column in the four boxes provided in Table 2.
| Activity | Length of air column (cm) |
| Resting 0 minute | 9.9 |
| 1 minute running on the spot | 9.8 |
| 2 minute running on the spot | 9.7 |
| 3 minute running on the spot | 9.6 |
(b) (i) State two different observations made from Table 2.
Observation 1: The length of air column during resting time is 9.9 cm
Observation 2: The length of air column after running on the spot for 3 min is 9.6 cm
(ii) State the inferences which correspond to the observation in 1(b) (i).
Inference from observation 1: During resting, the least CO2 is released and absorbed by potassium hydroxide solution
Inference from observation 2: During running on the spot for 3 min, the most CO2 is released and absorbed by potassium hydroxide solution
c) Complete Table 3 based on this experiment.
| Variable | Method to handle the variable |
| Manipulated variable Time of activity //
Type of Activity |
Use different time of activity, ie 0 minute, 1 minute, 2 minutes and 3 minutes // Resting and running on the spot |
| Responding variable Length of air column
|
Measure and record the length of air column using a metre rule. |
| Constant variable Same student
Initial length of air column |
Fix the same student to carry out all the activities Fix the length of air column to be 10 cm. |
(d) State the hypothesis for this experiment.
As the time of activity increases, the length of air column decreases/CO2 released increases
To be continued......
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