Fig. 1 shows a bell-jar model used by a class to represent breathing in a human. The two balloons represent lungs. A student pulls the rubber sheet at the b...
Question 1 Report
Fig. 1 shows a bell-jar model used by a class to represent breathing in a human. The two balloons represent lungs. A student pulls the rubber sheet at the bottom of the model downwards.
(a) Name the human structure represented by the rubber sheet. [1]
(b) Describe what happens to the volume of air inside the bell jar when the sheet is pulled down. [1]
(c) Explain why air enters the balloons when the sheet is pulled down. [3]
(d) Design an improvement to this model so that it represents the movement of the ribs during breathing in. [4]
Answer Details
(a) The rubber sheet represents the diaphragm. [1]
(b) Pulling the sheet down increases the volume of air inside the bell jar. [1]
(c) Pulling the sheet down increases the volume of the chest model. [1] The pressure inside becomes lower than atmospheric pressure. [1] Air moves into the balloons down this pressure gradient. [1]
(d) To model rib movement, use a flexible cage or box around the balloons. [1] Add hinged rods to represent ribs. [1] Attach material representing intercostal muscles, or strings that pull the ribs. [1] Pull the ribs upwards and outwards [1], increasing the volume around the balloons so air enters through the tube. [1] Any four valid points gain the marks.
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