Gaseous Exchange and Respiration in Animals
20 Grade 10 Biology questions on Gaseous Exchange and Respiration in Animals, with worked marking schemes. 20 questions are available on this topic in full.
Question 1
3 marksDescribe how expiration (breathing out) takes place in a human being at rest.
(3 marks)
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3 marksAn earthworm in a vegetable garden exchanges gases through its moist body surface, but a goat grazing in the same garden cannot rely on its skin and must use lungs. Account for this difference.
(3 marks)
Marking scheme
1 mark each, any three: (i) The earthworm is small and has a large surface area to volume ratio, so its body surface supplies enough oxygen; (ii) the earthworm is thin, so the diffusion distance from the surface to the innermost cells is short; (iii) the earthworm has a low metabolic rate and therefore a low oxygen demand; (iv) the goat is large with a small surface area to volume ratio, so its skin area is too small for its body mass; (v) the goat is warm blooded with a high metabolic rate and high oxygen demand; (vi) the goat's skin is dry, keratinised and waterproof, so internal lungs with a very large moist surface plus a blood transport system are needed. Maximum 3 marks.
Question 3
3 marksA herdsboy in Kajiado runs after a straying goat. Explain why his breathing becomes faster and deeper during the chase.
(3 marks)
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1 markThe human trachea is supported by rings of cartilage that are C-shaped rather than complete circles. The gap at the back of each ring is important because it
A. allows the oesophagus lying behind the trachea to bulge as swallowed food passes down
B. allows the trachea to collapse during expiration so that air is squeezed out
C. slows down air entering the bronchi so that it can be warmed
D. allows the trachea to produce mucus that traps dust
(1 mark)
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4 marksDescribe how a tilapia keeps a continuous stream of water flowing over its gills.
(4 marks)
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1 mark each, any four: (i) The fish opens its mouth and lowers the floor of the buccal cavity, increasing the volume and lowering the pressure inside it, while the opercular valves remain closed; (ii) water therefore flows in through the mouth into the buccal cavity; (iii) the mouth then closes and the floor of the buccal cavity is raised, reducing the volume and raising the pressure of the water; (iv) the water is forced backwards over the gill filaments and lamellae, where gaseous exchange takes place; (v) the raised pressure pushes the opercular valves open and the water leaves through the opercular openings; (vi) the two sets of movements alternate continuously, so water flows over the gills in one direction without stopping. Maximum 4 marks.
Question 6
1 markWhich combination of events takes place during inspiration in a human being?
A. The diaphragm muscles relax while the external intercostal muscles contract, raising the ribs upwards and outwards
B. The diaphragm muscles contract and the diaphragm flattens while the external intercostal muscles contract, raising the ribs upwards and outwards
C. The diaphragm muscles contract and the diaphragm domes upwards, decreasing the volume of the thoracic cavity
D. The internal intercostal muscles contract and the pressure inside the thoracic cavity rises above atmospheric pressure
(1 mark)
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1 markA grasshopper feeding in a maize shamba has no respiratory pigment in its blood, yet its flight muscles respire aerobically at a very high rate. This is possible because
A. fine tracheoles carry air directly to the respiring tissues, so oxygen does not have to be carried by blood
B. its blood transports oxygen dissolved in plasma at very high pressure
C. its flight muscles depend mainly on anaerobic respiration
D. oxygen is absorbed over the entire surface of its exoskeleton
(1 mark)
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1 markLong distance runners often camp at Iten, about 2,400 metres above sea level, where the air is thinner. After several weeks of training there, a blood test would most likely show
A. haemoglobin that releases its oxygen more slowly in the tissues
B. red blood cells that have retained their nuclei and therefore live longer
C. a larger volume of plasma so that more oxygen dissolves in it
D. an increase in the number of red blood cells, raising the oxygen carrying capacity of the blood
(1 mark)
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1 markMost of the carbon dioxide produced by respiring tissues in a human being is carried to the lungs
A. combined with the iron of haemoglobin in the red blood cells, in place of oxygen
B. unchanged as dissolved carbon dioxide, which accounts for nearly all of it
C. as bubbles of carbon dioxide gas suspended in the plasma
D. as hydrogen carbonate ions dissolved in the blood plasma
(1 mark)
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6 marksExplain how a molecule of oxygen in the air inside an alveolus reaches a mitochondrion in a calf muscle cell of the same person.
(6 marks)
Marking scheme
1 mark for each of the six points: (i) Oxygen is at a higher concentration in the alveolar air than in the blood of the surrounding capillary, giving a diffusion gradient; (ii) the oxygen dissolves in the moist alveolar lining and diffuses across the alveolar wall and the capillary wall, each one cell thick; (iii) it enters a red blood cell and combines with haemoglobin to form oxyhaemoglobin; (iv) the oxygenated blood is carried by the pulmonary vein to the left side of the heart and pumped through the aorta and arteries to the leg; (v) in the muscle capillaries the oxygen concentration is low and carbon dioxide high, so oxyhaemoglobin dissociates and releases the oxygen; (vi) the oxygen diffuses out of the capillary through the tissue fluid into the muscle cell and on to the mitochondrion, down a gradient kept steep by its continuous use in respiration. Total 6 marks.
Question 11
1 markIn a muscle cell of a goat, the first stage in the breakdown of glucose takes place in one part of the cell and the later stages, which require oxygen, take place in another. These two sites are respectively the
A. nucleus and the mitochondrion
B. mitochondrion and the cytoplasm
C. cytoplasm and the mitochondrion
D. cytoplasm and the ribosomes
(1 mark)
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1 markA learner runs a 400 metre race at the school sports day. For several minutes after crossing the finishing line she continues to breathe deeply and rapidly. The main reason for this is to
A. cool the body down after the vigorous exercise
B. take in extra oxygen to oxidise the lactic acid that accumulated in her muscles
C. get rid of the ethanol produced by her muscles during the race
D. replace the glucose that was used up by the muscles during the race
(1 mark)
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1 markA fisherman at Lake Victoria lands a tilapia and leaves it lying in the boat. The fish suffocates within a few minutes, even though air contains far more oxygen than lake water. Which statement best explains this?
A. Oxygen in air is too concentrated to be absorbed by the delicate gill membranes
B. The gill filaments and lamellae stick together out of water, greatly reducing the surface area available for gaseous exchange
C. The fish is unable to open and close its mouth once it is out of water
D. Air does not exert enough pressure to force oxygen into the gill capillaries
(1 mark)
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1 markIn the gills of a Nile perch, water flows over the gill lamellae in the direction opposite to the flow of blood in the lamellar capillaries. What is the main advantage of this arrangement?
A. It makes water flow faster over the gill surface
B. A concentration gradient for oxygen is maintained along the whole length of the lamella, so oxygen keeps diffusing into the blood
C. It stops carbon dioxide from re-entering the blood from the water
D. It equalises the oxygen concentration in the water and the blood so that further diffusion is unnecessary
(1 mark)
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4 marksExplain how the dense network of blood capillaries surrounding the alveoli and the continuous ventilation of the lungs together keep gaseous exchange going in a human being.
(4 marks)
Marking scheme
1 mark each, any four: (i) Blood flowing through the capillaries continuously carries oxygenated blood away, so oxygen concentration in the capillary blood stays lower than in the alveolar air; (ii) this maintains a steep diffusion gradient for oxygen from alveolus into blood; (iii) the arriving blood carries a high concentration of carbon dioxide, so carbon dioxide diffuses out of the blood into the alveolus down its own gradient; (iv) ventilation replaces used alveolar air with fresh air rich in oxygen and low in carbon dioxide; (v) both gradients are therefore maintained, so diffusion continues rapidly instead of stopping at equilibrium. Maximum 4 marks.
Question 16
3 marksState three uses to which the energy released during respiration is put in a mammal.
(3 marks)
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1 markA family sleeps in a tightly closed room with a charcoal jiko still burning inside, and in the morning they are found unconscious. The carbon monoxide from the jiko causes this because it
A. dissolves the walls of the alveoli so that diffusion can no longer take place
B. combines firmly with haemoglobin to form carboxyhaemoglobin, so the blood carries much less oxygen
C. dissolves in the plasma and blocks the blood capillaries
D. reacts with the oxygen in the alveoli and uses it up before it can diffuse
(1 mark)
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2 marksDistinguish between breathing and respiration as used in the study of animals.
(2 marks)
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4 marksDistinguish between aerobic and anaerobic respiration as they occur in a human muscle cell.
(4 marks)
Marking scheme
1 mark for each complete paired difference, any four: (i) Oxygen - aerobic requires oxygen, anaerobic occurs without oxygen; (ii) End products - aerobic gives carbon dioxide and water, anaerobic in muscle gives lactic acid; (iii) Extent of breakdown - aerobic breaks glucose down completely, anaerobic only partially; (iv) Energy released - aerobic releases a large amount of energy (about 2880 kJ per mole of glucose), anaerobic only a small amount (about 150 kJ per mole); (v) Site - aerobic stages occur mainly in the mitochondrion, anaerobic breakdown in the cytoplasm only. No mark for a one-sided statement. Maximum 4 marks.
Question 20
2 marksExplain why the inner lining of an alveolus is kept moist and why the wall of the alveolus is only one cell thick.
(2 marks)
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