A spirometer records the volume of air a person breathes. A student breathed normally into the spirometer shown in Fig. 6.1 and the volume of air in the mac...
Question 1 Report
A spirometer records the volume of air a person breathes. A student breathed normally into the spirometer shown in Fig. 6.1 and the volume of air in the machine was recorded, producing the trace and the readings in Table 6.1. The soda lime in the spirometer absorbed one of the gases from the breathed-out air. Six complete breaths were recorded in twelve seconds. The person wore a nose clip and breathed only through the mouthpiece so that all of the air passed through the machine. The soda lime removed one of the gases from the breathed-out air, and the trace was recorded steadily so that the volume of each breath could be read from the scale.
| Time / s | 0 | 2 | 4 | 6 | 8 | 10 | 12 |
|---|---|---|---|---|---|---|---|
| Volume / dm3 | 2.8 | 3.2 | 2.8 | 3.2 | 2.8 | 3.2 | 2.8 |
(a) Measure, using the volume scale in Fig. 6.1, the maximum volume shown on the trace. [1]
(b) Measure, using the volume scale in Fig. 6.1, the minimum volume shown. [1]
(c) Use your readings to state the tidal volume of one breath. [1]
(d) Determine the breathing rate in breaths per minute from Table 6.1. Show your working. [2]
(e) Calculate the pulmonary ventilation (breathing rate multiplied by tidal volume). Show your working. [2]
(f) Record the name of the instrument used. [1]
(g) Name the gas absorbed by the soda lime and explain why it is removed. [2]
(h) Over several minutes the baseline of the trace slowly fell. Explain why. [2]
(i) The baseline fell by 1.5 dm3 over 3 minutes. Calculate the rate of oxygen use in dm3 per minute. Show your working. [2]
(j) Explain why the mouthpiece must have a tight seal and the person should wear a nose clip. [2]
(k) Describe what is meant by vital capacity. [2]
(l) State two variables that should be controlled when two people are compared. [2]
Answer Details
This question tests reading a spirometer trace, breathing calculations, and how the apparatus works.
(a) The trace's maximum (top of each breath) reads 3.2 dm³ [1].
(b) The trace's minimum (bottom of each breath) reads 2.8 dm³ [1].
(c) Tidal volume is one breath, i.e. maximum minus minimum: \[3.2 - 2.8 = 0.4\ \text{dm}^3\] so the tidal volume is 0.4 dm³ [1].
(d) Six breaths were taken in 12 seconds. Scale this to one minute (60 s): \[\frac{6}{12}\times 60 = 30\ \text{breaths per minute}\] Working [1], answer 30 breaths/min [1]. [2]
(e) Pulmonary ventilation = breathing rate × tidal volume: \[30 \times 0.4 = 12\ \text{dm}^3\ \text{per minute}\] Working [1], answer 12 dm³/min [1]. [2]
(f) The instrument is a spirometer [1].
(g) The soda lime absorbs carbon dioxide [1]; it is removed so it is not rebreathed / so that the fall in the total volume shows only the oxygen used [1]. [2]
(h) The baseline slowly falls because oxygen is taken from the spirometer air and used in respiration [1], while the carbon dioxide breathed out is absorbed by the soda lime, so the total volume of air falls [1]. [2]
(i) Rate of oxygen use = volume fall over time: \[\frac{1.5\ \text{dm}^3}{3\ \text{min}} = 0.5\ \text{dm}^3\ \text{per minute}\] Working [1], answer 0.5 dm³/min [1]. [2]
(j) A tight seal and nose clip are needed so that no air leaks in or out through the mouth or nose [1], so that all the air breathed passes through the spirometer and the readings are accurate [1]. [2]
(k) Vital capacity is the maximum volume of air breathed out [1] after the deepest possible breath in [1]. [2]
(l) Any two variables to control when comparing two people: age, sex, fitness, body size, whether at rest or after the same activity [2].
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