The diagram shows a model used by a class to demonstrate breathing. The bell jar represents the chest, two balloons represent the lungs and the rubber sheet...
Question 1 Report
The diagram shows a model used by a class to demonstrate breathing. The bell jar represents the chest, two balloons represent the lungs and the rubber sheet represents the diaphragm. A student pulls the rubber sheet down while another student watches the balloons. The tube is sealed through the cap at the top of the jar so that air can enter only through the tube.
(a) Name the structures labelled A, B and C. [3]
(b) Describe what happens to the volume of the box, the pressure of air inside it and the balloons when the rubber sheet is pulled down. [4]
(c) Explain how breathing in allows oxygen to be used by human cells to release energy. [5]
(d) Use Fig. 3 to explain three limitations of this model of breathing. [3]
(e) Suggest how the students could use limewater to show that exhaled air contains more carbon dioxide than inhaled air. [3]
Answer Details
(a) A is the bell jar, representing the chest. B is a balloon, representing a lung. C is the rubber sheet, representing the diaphragm. [3]
(b) Pulling the rubber sheet down increases the volume inside the bell jar. The pressure of air inside decreases, so air enters through the tube. The balloons inflate and increase in volume. [4]
(c) Air containing oxygen enters the lungs during inhalation. Oxygen reaches the alveoli, then diffuses into capillary blood. The blood transports oxygen to body cells, where oxygen is used in aerobic respiration to release energy. [5]
(d) The model has limitations: the bell jar is rigid, whereas the rib cage moves during breathing; the rubber sheet is pulled, whereas the real diaphragm is a muscle that contracts and becomes flatter; and the balloons do not show alveoli, capillaries or gas exchange. It also does not show blood flow or transport by the heart. Any three are required. [3]
(e) Pass equal volumes of inhaled and exhaled air through separate equal volumes of limewater, keeping conditions the same. Exhaled air makes limewater turn cloudy faster or become cloudier. This indicates that exhaled air contains more carbon dioxide. [3]
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