HKDSE Biology Ch. 7 Gas Exchange in Humans Worksheet Answer Key PDF

HKDSE Biology Ch. 7 Gas exchange in humans Answer 7.1 The human breathing system respiration / oxygen / carbon dioxide diffusion / moist large Question: Draw arrows to indicate the gas exchange in Amoeba on the right. Label the gases involved. (i) breathing system (ii) transport system Questio...

HKDSE Biology Ch. 7 Gas exchange in humans Answer 7.1 The human breathing system respiration / oxygen / carbon dioxide diffusion / moist large Question: Draw arrows to indicate the gas exchange in Amoeba on the right. Label the gases involved. (i) breathing system (ii) transport system Question: Label the structures in human breathing system. 1  HKDSE Biology Ch. 7 Gas exchange in humans Question: With the letters provides, identify the various structures with reference to the directions of airflow along the respiratory tract: G → E → D → A→ C → F → B Question: With reference to the photos on the right, is it better to breathe through the nostrils or the mouth? Explain your answer. Nostrils. Hairs in the nostrils and mucus in the nasal cavity trap dust particles and microorganisms in the incoming air. The mouth cavity does not have such features to filter the incoming air. Note: There are no hairs in nasal cavity which is lined with mucus-secreting cells, ciliated epithelial cells and capillaries] Question: Name cell X and cell Question: With reference to the features of the lining shown in the Y. (2 marks) photomicrograph, describe how the lining of the nasal cavity can protect human body against bacterial invasion. (3 Cell X: ciliated epithelial cell marks) Cell Y: mucus-secreting cell 2  HKDSE Biology Ch. 7 Gas exchange in humans Question: Label the structures in trachea, bronchi and bronchioles. Question: With reference to the magnifications of the photomicrographs, arrange the lumen size of the above three structures in descending order. Trachea (x 10) > Bronchus (x20) > Bronchiole (x 60) Remark: Trachea has the lowest magnification to have a lumen size comparable to the other two structures. This indicates that trachea has the largest lumen size. 3  HKDSE Biology Ch. 7 Gas exchange in humans Question: Account for the different shapes of cartilages in Question: Which part is mostly affected trachea and bronchus. by the contraction and relaxation of the The trachea is supported by C-shaped cartilages, while smooth muscles: the trachea, the bronchus is supported by circular rings of cartilages. The bronchus or the bronchiole? Explain. back of the trachea is attached closely to the oesophagus. The bronchiole because it has no cartilage The part of the tracheal wall in contact with the oesophagus to restrict the contraction and relaxation of has no cartilage. This allows flexible extension of the the smooth muscle. oesophagus during swallowing. Practical 7.2 Examination of pig lungs (Textbook P.7-10) Procedure & Question Answer 1. Examine the pig lungs. Pink. There are many capillaries in the lungs. The What is the colour of the lungs? capillaries contain blood. 2. Examine the pig lungs. There are two or three lobes in the left lung and four How many lobes are there in the left lungs lobes in the right lung. and the right lung? 3. Are the trachea and the lung tissue hard or The trachea is hard. The lung tissue is sort and spongy. soft? Why? The trachea, but not the lung tissue, is supported by cartilages. 4. What is the change in the volume of the lungs The lungs increase in volume. when water is pumped into them? 5. Cut a piece of lung tissue. Use a syringe to The lungs increase in volume. inject air through a bronchiole of the cut tissue. What is the change in volume of the tissue? 6. Cut another piece of lung tissue and put it into The piece of lung tissue floats in water. The air in the water and observe if it floats or sinks. Why? air sacs of the lungs gives the lung tissue a low density. 7.2 Gas exchange in the air sacs Question: What is the importance of containing elastic fibres in lung tissue for the lungs to perform the function? When one inhales, the elastic fibres stretch to allow the lungs to inflate. When we exhale, the recoiling of the stretched elastic fibres (known as elastic recoil) helps force air out of the lungs. Blood from pulmonary artery; blood to pulmonary veins Capillary; red blood cell 4  HKDSE Biology Ch. 7 Gas exchange in humans Question: With reference to the diagram in Question: If a person breathes deeply, how will the volume of the previous page, describe how oxygen in tidal air inhaled be affected? Explain the effect of deep the tidal air reaches the blood. breathing on the rate of oxygen uptake in the blood. Hence, or (3 marks) otherwise, explain the effect of smoking on the process of oxygen reaching the blood. (4 marks) Oxygen in the tidal air diffuses through The volume of tidal air will increase. (1) The oxygen uptake the residual air (1) in the blood becomes faster because the distance of diffusion And dissolve in the water film lining the of oxygen from the tidal air to the water film is reduced air sac (1) /because the surface area of the air sac for diffusion of It then diffuses across the walls of the oxygen is increased. (1) air sac and the capillary into the blood Tar deposit on the wall of the air sac (1) would reduce the (1) rate of diffusion of oxygen. (1) Question: A jar of atmospheric air sample and a jar of exhaled air sample are collected. Describe what should be done to compare the oxygen content of the two air samples. Put a burning candle / splint into the gas samples. (1) Compare the time that the candle can burn. (1) Note: The candle in both sample will not relight if a glowing splint is used for testing. Differences in compositions between inhaled air and exhaled air Inhaled air Exhaled air Explanation for the difference 21% 16% Oxygen is used by body cells for respiration. 0.04% 4% Carbon dioxide is produced by body cells during respiration. 78% 78% Nitrogen is not used nor produced by body cells. Exhaled air is moistened by the water film lining the air sacs and the Variable Saturated mucus lining the respiratory tract. 1% 1% These gases are not used nor produced by body cells. Exhaled air is warmer than inhaled air because exhaled air is warmed by the blood in the capillaries. Question: Mouth to mouth ventilation is a method for rescuing a person who fails to breathe but still has heartbeat. It involves blowing exhaled air into the patient’s body through the mouth (diagram on the left). Explain why this method can help the patient stay alive before he can breathe again. Exhaled air still contains 16% oxygen. When blown into the patient’s lungs, the oxygen can be supplied to the body cells for respiration. 5  HKDSE Biology Ch. 7 Gas exchange in humans Question: Draw arrows on this diagram to show the direction which air would take in passing through the set-up. Question: Describe and explain the expected results of the experiment. The hydrogencarbonate indicator in Y turns yellow while that in X remains red. This is because exhaled air contains more carbon dioxide than inhaled air. Question: Suggest another reagent that can be used to replace hydrogencarbonate indicator. Describe the expected result if the reagent is used. Lime water. The lime water in Y turns milky while that in X remains clear. 6  HKDSE Biology Ch. 7 Gas exchange in humans Photomicrograph of human lung Question: With reference to two features observable in the photomicrograph, explain how the lung tissue is adapted to gas exchange. Any two of the following: The lung tissue has numerous air sacs. This provides a large surface area for gas exchange or diffusion of gases. The wall of air sac is very thin so as to reduce the distance of diffusion of respiratory gases between air and blood. The lung tissue is richly supplied with blood capillaries. This allows a rapid transport of gases to and away from the air sacs. Therefore a steep concentration gradient of gases is maintained between the air in A and the blood. Question: Compare the oxygen and glucose content of the blood in vessels A and B. Explain your answer. A contains more oxygen than B (1) because gas exchange takes place at air sacs where oxygen is taken up by blood through diffusion (1), blood leaving air sac should have more oxygen A contains less glucose than B (1) because the cells in air sacs / lung tissues have taken up glucose from blood for respiration (1), blood leaving air sac should have less glucose Question: With reference to the above information about the lung disease, suggest the possible ways in which the disease adversely affects gas exchange in the patient. dust deposit forms a barrier (1) which increases the diffusion distance (1) the inner surface of the air sacs was covered by dust (1), thus the area available for diffusion was reduced (1) the hardened layer of dust deposit reduces the elasticity of the lung (1), hence a smaller lung volume when the lung inflates (1) Question: What is structure A? Air sac Question: With reference to the photographs, explain how the function of structure A is affected by cigarette smoking. The number/surface area of structure A is reduced / the surface of structure A of the smoker is less folded which greatly reduces the rate of gas exchange 7  HKDSE Biology Ch. 7 Gas exchange in humans 7.3 Transport of respiratory gases Red blood cells and haemoglobin  Oxygen is mainly transported by red blood cells in the blood. Question: Why does the centre of the red blood cell look more pale than the other part? As red blood cell has a biconcave shape, there is less cytoplasm in the centre part and so more light are able to pass through the cell, and so this part looks more pale than the other part. Question: Adaptive features of red blood cells for carrying oxygen: I: d II: a & c III: b Question: Compare the affinity of haemoglobin for carbon monoxide and oxygen. The affinity of haemoglobin for carbon monoxide is higher than that of oxygen. The combination of haemoglobin and carbon monixoide is irreversible but that of haemoglobin and oxygen is reversible. Uptake of oxygen from air sacs in the lungs high / oxyhaemoglobin / pulmonary veins Release of oxygen to body cells in body tissues low / pulmonary artery Release of carbon dioxide to air sacs in the lungs low / carbon dioxide Uptake of carbon dioxide from body cells in body tissues water / hydrogencarbonate ions / enzyme 8  HKDSE Biology Ch. 7 Gas exchange in humans 7.4 Ventilation Question: What is Inhalation / Inspiration Exhalation / Expiration the principle of air flow? intercostal intercostal Along air pressure muscle muscle gradient (from higher thoracic thoracic pressure region to cavity cavity lower pressure region) diaphragm diaphragm Intercostal muscles contract relax Rib cage moves upwards and outwards moves downwards and inwards Diaphragm muscles contract relax Diaphragm flattens Returns to dome shape Thoracic cavity and Volume of thoracic cavity Volume of thoracic cavity decreases. and lungs increases and in turn causes an causes a decrease in the volume of the increase in the volume of lungs. lungs. (The inner wall of the (The elastic fibres of the lungs that have thoracic cavity and the outer been stretched during inhalation recoil) surfaces of the lungs are held together by pleural membranes and pleural fluid). Air pressure in the Air pressure in the lungs Air pressure in the lungs increases and lungs decreases and becomes lower becomes higher than the atmospheric than the atmospheric pressure pressure Direction of air flow Air rushes into the lungs Air is forced out of the lungs Question: Which type of muscle do intercostal muscles and diaphragm muscles belong to? Skeletal muscles. They are attached to the ribs (skeleton) and could be controlled voluntarily (e.g. holding the breath, deep breathing) Question: Identify inhalation and exhalation. A: inhalation B: exhalation C: inhalation D: exhalation 9  HKDSE Biology Ch. 7 Gas exchange in humans Question: State the periods when inhalation occurs. Explain how you arrive at your answer. 0 – 2 s & 4 – 6 s. These are periods in which the air pressure in lungs is higher than that of atmospheric pressure. Question: State the times when the volume of lungs is the largest. 2nd second and 6th second. (Note: the moments just before exhalation) Volume of lungs and the pressure of lungs during breathing Question: Using the information on the graph, Question: Using the information on the graph, calculate the rate of breathing (in breaths per minute) calculate the rate of breathing (in breaths per minute) of Person A who is taking a rest. Show your working. of Person B. (Hint: one breath consists of one inhalation and one exhalation) Rate of breathing of person B Rate of breathing of person A = 60 / 2 = 60 / 4 = 30 breaths / minute = 15 breaths / minute Question: With reference to the graphs above, compare the breathing pattern of person A and person B? The rate of breathing and depth of breathing for person B is higher than that of person A. Question: If the rate of breathing is 20 breaths per minute, sketch the change in air pressure in the graph below. (One complete breath (one inhalation and exhalation) lasts for 3 seconds If the pleural membrane on the left side of the boy’s thorax is punctured, his left lung will collapse while his right lung will not. Question: What would be the change in his breathing movement? The breathing movements would become faster Question: What would be the air flow of his left and right lungs respectively? Left lung: In the left lung, air flow would decrease Right lung: In the right lung, air flow would increase Remark: Only left lung collapse while his right lung will not because each lung is surrounded by its own pleural membranes. 10  HKDSE Biology Ch. 7 Gas exchange in humans 1 Rib-cage model ◼ In the model, the vertical rods represent the vertebral column and the sternum. The horizontal rods represent the ribs. The rubber band represents the intercostal muscles. Question: What are the limitations of this model to represent the actual conditions in the human body? - The area bounded by the rods is two-dimensional space while the thoracic cavity is a three- dimensional space. - The external force needs to be applied to move the rods while in the human body the intercostal muscles contract and relax to move the ribs. 2 Bell-jar model ◼ In the model, the glass tube represents the trachea. The wall of the bell jar represents the thoracic wall. The balloons represent the lungs. The rubber sheet represents the diaphragm. Question: What are the limitations of this model to represent the actual conditions in the human body? - The glass tube is rigid and inflexible while the trachea is flexible. - The bell jar has a fixed shape while the rib cage can move upwards and outwards to increase the volume of the thoracic cavity. - The space of the bell jar is filled with air while the pleural cavity is filled with the pleural fluid. - The balloons are large open spaces while the lungs are made up of millions of individual air sacs. - The rubber sheet is pulled downwards while the diaphragm only flattens. 11