Gas exchange in humans Banker

1. (a) Which row shows the approximate percentages of oxygen and carbon dioxide in expired air?A oxygen 21 %, carbon dioxide 0.04 %B oxygen 16 %, carbon dioxide 4 %C oxygen 4 %, carbon dioxide 16 %D oxygen 0.04 %, carbon dioxide 21 % [1]

1. (a) State two differences, other than gas percentages, between inspired and expired air. [2]
2. (b) Explain why expired air contains less oxygen and more carbon dioxide than inspired air. [3]

1. (a) Name the gas that makes up about 78 % of both inspired and expired air. [1]
2. (b) Explain why the percentage of nitrogen hardly changes between inspired and expired air. [1]
3. (c) State the percentage of carbon dioxide in inspired air. [1]

1. (a) What happens during inspiration?A The diaphragm relaxes and becomes dome-shaped.B The external intercostal muscles contract and the ribs move up and out.C The volume of the thorax decreases and the pressure increases.D The internal intercostal muscles contract and the ribs move down. [1]

1. (a) Describe the roles of the diaphragm and the intercostal muscles in inspiration. [4]
2. (b) Describe how forced expiration, for example when blowing up a balloon, differs from quiet expiration. [2]

A student breathes in and out gently through a mouthpiece connected to two boiling tubes of limewater, X and Y. Valves make air breathed in pass through tube X and air breathed out pass through tube Y.

1. (a) Describe the colour change expected in tube Y (breathed out into) and explain it. [2]
2. (b) Tube X (air breathed in through) also turned slightly cloudy after a much longer time. Explain why. [1]
3. (c) State two variables that should be controlled to make the comparison fair. [2]
4. (d) Suggest a safer and more sensitive indicator that could replace limewater, and state its colour in expired air. [2]

A model of the thorax is made from a glass bell jar with a rubber sheet across the open bottom. Two balloons are attached to a Y-shaped glass tube passing through a stopper at the top.

1. (a) State what happens to the volume and the pressure inside the bell jar (representing the thorax) when the rubber sheet is pulled down. [2]
2. (b) State what happens to the balloons and explain why. [2]
3. (c) Name the part of the body represented by (i) the rubber sheet, (ii) the balloons, (iii) the glass tube. [3]
4. (d) Give one way in which the model does not show breathing accurately. [1]

1. (a) Air moves into the lungs during inspiration becauseA the lungs expand by themselves and suck air in.B the pressure inside the lungs falls below atmospheric pressure.C the alveoli actively pump air inwards.D oxygen diffuses down a concentration gradient into the trachea. [1]

1. (a) Calculate the volume of oxygen taken into the blood each minute, in cm³, when the person breathes 12 times per minute with a tidal volume of 500 cm³. Use inspired air 21 % oxygen and expired air 16 % oxygen. [3]
2. (b) Suggest why the oxygen percentage of expired air is not close to 0 %, even though the blood leaving the lungs is almost saturated with oxygen. [2]

A student analysed samples of air with a gas analyser. Mean results: inspired air – oxygen 21.0 %, carbon dioxide 0.04 %; expired air – oxygen 16.0 %, carbon dioxide 4.0 %.

1. (a) Calculate the percentage of the inspired oxygen that was absorbed by the body. [2]
2. (b) Calculate how many times greater the carbon dioxide concentration was in expired air than in inspired air. [1]
3. (c) Suggest why the student analysed three samples of each and calculated a mean. [1]

1. (a) Explain what happens to breathing if the external intercostal muscles were paralysed but the diaphragm still worked. [2]
2. (b) Suggest why a puncture wound through the chest wall into the space around one lung (pleural cavity) can cause that lung to collapse. [2]

1. (a) Which sequence shows the correct pathway of air into the lungs?A larynx → trachea → bronchioles → bronchi → alveoliB larynx → trachea → bronchi → bronchioles → alveoliC trachea → larynx → bronchi → bronchioles → alveoliD larynx → bronchi → trachea → bronchioles → alveoli [1]

1. (a) State four features of gas exchange surfaces in animals. [4]
2. (b) For one of these features, explain how it is achieved in human lungs. [1]

1. (a) Name the structure described: (i) the box-shaped organ at the top of the trachea that contains the vocal cords; (ii) the tiny air sacs where gas exchange occurs; (iii) the narrow tubes that branch from the bronchi. [3]
2. (b) State the name of the blood vessels that surround each alveolus. [1]

1. (a) What is the function of the C-shaped rings of cartilage in the trachea?A They trap dust and pathogens.B They keep the trachea open during changes in pressure.C They produce mucus.D They allow gas exchange with the blood. [1]

1. (a) State the function of (i) goblet cells and (ii) ciliated cells in the trachea. [2]
2. (b) Tobacco smoke paralyses cilia. Explain why smokers are more likely to suffer from chest infections. [3]

1. (a) Calculate the surface area to volume ratio of a single spherical alveolus of radius 0.1 mm. Use surface area = 4πr² and volume = 4/3πr³. Give your answer in mm⁻¹. [2]
2. (b) Explain why lungs made of millions of small alveoli are more efficient than lungs made of one large sac of the same total volume. [2]

1. (a) Explain why the gas exchange surface in the lungs must be kept moist. [1]
2. (b) Describe how carbon dioxide moves from the blood plasma into the alveolus. [2]
3. (c) Explain why the concentration gradient for oxygen between alveolar air and the blood is maintained. [2]

1. (a) Explain how the structure of an alveolus and its capillary make diffusion of oxygen into the blood rapid. [4]
2. (b) In emphysema the walls between neighbouring alveoli break down, forming fewer, larger air sacs. Explain why people with emphysema become breathless during mild exercise. [2]

A student examines fresh sheep lungs, attached to the trachea, obtained from a butcher's shop in Rawalpindi.

1. (a) Suggest how the student would show that the trachea is held open by cartilage. [2]
2. (b) When the student pumps air into the lungs through the trachea with a bellows, the lungs inflate, then deflate when the bellows are removed. Explain why they deflate. [1]
3. (c) State one safety or hygiene precaution when handling fresh animal tissue. [1]

1. (a) An adult's lungs contain about 480 million alveoli, each with a surface area of 0.15 mm². Calculate the total surface area in m². (1 m² = 1 000 000 mm²) [2]
2. (b) In cystic fibrosis the mucus in the airways is very thick and sticky. Suggest and explain two effects this has on gas exchange and health. [4]

1. (a) Which change in the blood is detected by the brain and causes an increase in the rate and depth of breathing during exercise?A an increase in glucose concentrationB an increase in carbon dioxide concentrationC a decrease in carbon dioxide concentrationD an increase in oxygen concentration [1]

1. (a) Describe how the breathing changes during exercise. [2]
2. (b) Explain why these changes are needed. [3]

1. (a) State which part of the body detects an increase in carbon dioxide concentration in the blood and controls breathing. [1]
2. (b) State two effects on breathing when the carbon dioxide concentration in the blood rises. [2]
3. (c) Suggest why it is dangerous to allow carbon dioxide to build up in the blood. [1]

1. (a) A runner's breathing rate stays high for several minutes after finishing a race. What is the main reason?A The muscles are still contracting strongly.B Extra oxygen is needed to break down lactic acid built up during anaerobic respiration.C The lungs need time to fill with carbon dioxide.D Glucose must be absorbed from the gut. [1]

A student in Quetta measured her breathing rate three times at rest and three times immediately after 2 minutes of skipping.At rest (breaths per minute): 14, 16, 15After exercise: 30, 33, 30

1. (a) Calculate the mean breathing rate at rest and after exercise. [2]
2. (b) Calculate the percentage increase in mean breathing rate. Give your answer to 2 significant figures. [2]
3. (c) Describe how the student should measure the breathing rate. [2]
4. (d) State two variables that should be kept constant. [2]

A football player in Lahore wore a mask attached to a breathing monitor.At rest: rate 14 breaths per minute, tidal volume 0.5 dm³After 6 minutes of exercise: rate 28 breaths per minute, tidal volume 2.1 dm³Breathing rate 2, 4, 6 and 8 minutes after exercise stopped: 24, 20, 16, 14 breaths per minute

1. (a) Calculate the increase in tidal volume between rest and 6 minutes of exercise. [1]
2. (b) Describe the changes in breathing rate after the exercise stopped. [2]
3. (c) Explain why the breathing rate did not return to the resting value immediately after exercise. [3]

1. (a) Explain how physical activity leads to an increase in the rate and depth of breathing. [4]
2. (b) Calculate the volume of air breathed per minute at rest (12 breaths per minute, 0.5 dm³ per breath) and during exercise (30 breaths per minute, 2.4 dm³ per breath). State how many times greater the exercise value is. [3]

1. (a) Plan an investigation to find the effect of the duration of exercise on breathing rate in students. Include the variables, the method and how you would make the results reliable. [6]

Two students did the same 3-minute exercise. Breathing rates / breaths per minute:Resting (3 readings): A – 16, 15, 17; B – 12, 14, 22Minutes after exercise 2, 4, 6, 8: A – 30, 22, 16, 16; B – 20, 13, 13, 12

1. (a) Identify the anomalous result and calculate the mean resting breathing rate of student B without it. [2]
2. (b) State how many minutes after exercise each student's breathing rate first returned to within 1 breath per minute of their resting mean (A resting mean 16). [2]
3. (c) Suggest which student is fitter and give one reason. [2]