INTERNATIONAL TURKISH HOPE SCHOOL 2014 2015 ACADEMIC YEAR CHITTAGONG SENIOR SECTION RESPIRATION and GAS EXCHANGE CLASS IX and X Name :... Date :... SYLLABUS CONTENT Section 2: Structures and functions in living organisms f) Respiration Students will be assessed on their ability to: 2.33 recall that the process of respiration releases energy in living organisms 2.34 describe the differences between aerobic and anaerobic respiration 2.35 recall the word equation and the balanced chemical symbol equation for aerobic respiration in living organisms 2.36 recall the word equation for anaerobic respiration in plants and in animals 2.37 describe simple controlled experiments to demonstrate the evolution of carbon dioxide and heat from respiring seeds or other suitable living organisms. g) Gas exchange 2.38 understand the role of diffusion in gas exchange Flowering plants 2.39 understand gas exchange (of carbon dioxide and oxygen) in relation to respiration and photosynthesis 2.40 understand that respiration continues during the day and night, but that the net exchange of carbon dioxide and oxygen depends on the intensity of light 2.41 explain how the structure of the leaf is adapted for gas exchange 2.42 describe the role of stomata in gas exchange 2.43 describe simple controlled experiments to investigate the effect of light on net gas exchange from a leaf, using hydrogen-carbonate indicator Humans 2.44 describe the structure of the thorax, including the ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli and pleural membranes 2.45 understand the role of the intercostal muscles and the diaphragm in ventilation 1 P a g e
2.46 explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and blood in capillaries 2.47 understand the biological consequences of smoking in relation to the lungs and the circulatory system 2.48 describe a simple experiment to investigate the effect of exercise on breathing in humans. HUMAN BIOLOGY 7. Respiration a) Recall that the process of respiration releases energy in living organisms. b) Explain the differences between aerobic and anaerobic respiration. c) Recall the word equation and the balanced chemical symbol equation for aerobic respiration in living organisms. d) Describe how to carry out simple controlled experiments to demonstrate the evolution of carbon dioxide in respiration. e) Describe the breakdown and regeneration of ATP. f) Explain the formation of lactic acid in anaerobic respiration. 8. Gas exchange a) Recall the structure of the thorax, including the ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli and pleural membranes. b) Explain the role of the intercostal muscles and the diaphragm in ventilation. c) Explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and blood in capillaries. d) Explain the term lung capacity, including vital capacity, tidal volume and explain spirometer traces of breathing movement. e) Explain the regulation of carbon dioxide and oxygen content in the blood. f) Understand the biological consequences of smoking in relation to the lungs and the circulatory system. g) Describe how to carry out simple experiments to investigate the effect of exercise on breathing in humans, including the use of limewater or bicarbonate indictor. h) Understand the effects of exercise and the benefits of regular exercise. 2 P a g e
Respiration: the chemical reactions that break down nutrient molecules in living cells to release energy. Uses of energy in the body of humans: muscle contraction, protein synthesis, cell division, active transport, growth, the passage of nerve impulses and the maintenance of a constant body temperature. Aerobic respiration Aerobic respiration: the release of a relatively large amount of energy in cells by the breakdown of food substances in the presence of oxygen. Glucose + oxygen carbon dioxide + water C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O Anaerobic respiration Anaerobic respiration: the release of a relatively small amount of energy by the breakdown of food substances in the absence of oxygen. In muscles: glucose lactic acid C6H12O6 2 C3H6O3 In yeast (microorganism, a single-cell fungi): glucose ethanol + carbon dioxide C6H 12 O 6 2C 2 H 5 OH + CO 2 Brewing (wine): 1) Grapes (sugar source) are pressed to allow enzymes to begin fermentation 2) Yeast converts sugar into alcohol. 3) At 8-9% the alcohol (which is toxic) kills the yeast, (higher concentrations of alcohol are achieved by distillation) Bread making: 1) Flour, sugar, water and salt are mixed with yeast to make the dough. 2) The dough is kept in a warm, moist environment (28 C). The yeast ferments sugar making carbon dioxide which creates bubbles, so the bread rises. 3) 3) Cooking (at 180 C) kills yeast, evaporates alcohol and hardens outer surface. Disadvantages of anaerobic respiration: -only produces 1/20 of the energy per glucose molecule that aerobic respiration would -produces poisonous lactic acid Lactic acid: is transported in the blood to the heart, liver and kidneys, which oxidise it. The heart, liver and kidneys need extra oxygen to do this which causes you to continue breathing heavily after exercise. The extra oxygen is called the oxygen debt. 3 P a g e
Property of surface Thin (ideally one cell thick) Large surface area Moist Well ventilated Close to blood supply Reason short distance to diffuse many molecules can diffuse at the same time cells die if not kept moist concentration gradients for oxygen and carbon dioxide are kept up by regular fresh supplies of air gases can be carried to/from the cells that need/produce them Inhaled (inspired) air: 21% oxygen, 0.04% carbon dioxide, 78% nitrogen and water vapour varies to climate Exhaled (expired) air: 18% oxygen, 3% carbon dioxide, 78% nitrogen, and saturated water vapour. Demonstrate CO 2 s presence in exhaled air: blowing bubbles through a straw into a test tube with limewater (aqueous calcium hydroxide) giving a white precipitate (calcium carbonate). Physical activity increases the breathing rate more breaths per minute, and the tidal volume more air per breath, this is measured with a spirometer to produce a spirogram. During exercise, tissues respire at a higher rate, the change in breathing volume and rate helps to keep CO 2 concentration and ph at safe levels. 4 P a g e
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Breathing in: (RICE) 1) external intercostal muscles contract pulls rib cage upwards and outwards 2) diaphragm muscles contract diaphragm moves upwards 3) Lung volume increases and pressure falls (Boyle s law: pressure and volume are inversely proportional) 4) Air rushes in to equalise pressures. Breathing out: (ERIC) 1) external intercostal muscles relax rib cage falls downwards and inwards 2) diaphragm muscles relax returns to dome shape 3) Lung volume decreases and pressure increases 4) Air is forced out Internal intercostal muscles: are used in coughing and sneezing. Mucus & cilia: goblet cells produce sticky mucus to trap and eliminate particulate matter and microorganisms. Ciliated cells have cilia: little hairs which sweep back and forward in a coordinated way to brush mucus up the lungs into the mouth. The differences between aerobic and anaerobic respiration are shown in the table below: Aerobic respiration Anaerobic respiration Oxygen gas is used in aerobic respiration. No oxygen gas is used during anaerobic respiration. No alcohol or lactic acid is made. Alcohol or lactic acid is made. Large amount of energy(atp) is released. Small amount of energy(atp) is released. Carbon dioxide is always made. Carbon dioxide is sometimes made. The process begins in the cytoplasm and The process occurs in the cytoplasm. continues into the mitochondria. Glucose+Oxygen Carbon Dioxide+Water+ATP Glucose Alcohol+Carbon Dioxide (in Yeast) Glucose Lactic Acid+ATP (in Muscles) ***ANAEROBIC RESPIRATION in YEAST is also known as FERMENTATION*** [NOTE: Glucose is the main raw material for respiration. In the presence of oxygen, glucose is broken down completely by a process called complete breakdown. In insufficient oxygen, glucose is broken down partially forming intermediate products by a process called incomplete breakdown. The main product of respiration is energy.] [Note: either limewater or hydrogen-carbonate indicator solution can be used for testing the presence of Carbon Dioxide. Limewater changes from clear to cloudy when carbon dioxide dissolves in it. Hydrogen carbonate indicator solution changes from red to yellow when carbon dioxide dissolves in it.] 6 P a g e
Describe a simple experiment to investigate the effect of exercise on breathing in humans. 1. The person carrying out the experiment is to sit quietly for two minutes to make sure that he or she is completely relaxed. 2. The number of breaths taken per minute is to be counted and recorded. 3. The person is to wait for one minute, and then again count the number of breaths and record. 4. Then, some vigorous exercise is to be done for exactly two minutes.at the end of this time, the person is to sit down.the number of breaths taken in the immediate next minute is to be recorded. 5. Recording the breaths per minute is to be continued every other minute, until they have returned near the level before exercising was started. On comparing the results of the number of breaths taken per minute before and after exercising, it will be seen that exercise causes the breathing rate in humans to increase. 7 P a g e
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1. Explain how a human performs each of the processes in the sequence given below. Starting from the digestion of starch. The release, during exercise in that muscle cell, of the energy in those molecules. [5marks] Ans: During digestion starch molecules break down into maltose, which are then digested by maltase enzyme into glucose. These glucose molecules are absorbed through villi present on the inner surface of the small intestine. The glucose molecules are transported through the blood circulation and are converted into glycogen in the liver and muscle. The glycogen can be converted into glucose by the action of glucagons and the aid of adrenalin. In an exercising muscle, cells need a lot of energy very quickly. To provide this energy the mitochondria in the muscle cells will be combining oxygen with glucose as fast as they can during aerobic first. Glucose + Oxygen Carbon dioxide + Water + Energy (2898 kj) To supply more energy anaerobic respiration occurs in the muscle. A lot of lactic acid and less amount of energy is produced during anaerobic respiration. Glucose Lactic acid + Energy (210 kj) 2. (a) Why do living cells respire? [2 marks] Ans: Living cells respire to breakdown the complex organic substance ( mainly carbohydrates) by oxidation to obtain the required energy which a body uses in its several metabolic activities along with carbon dioxide and water. 2.(b) Describe an experiment by which you could find out whether a green plants release carbon dioxide. Ans: Name of the experiment: To show that a green plant release carbon dioxide. [6marks] Diagram: Procedure: The apparatus is set up as shown in the diagram. A potted plant is placed in flask C. The vessel containing plant must be blacked out to prevent photosynthesis. In case of potted plant the pot must be enclosed by impermeable material with Vaseline seal so that respiration in organisms in the soil does not affect the result. A suction pump is used to suck out the air through delivery tube E. This causes air to be drawn into flask A. The air flows through the apparatus as shown by the arrows. Observation: The air from flask C should turn the lime water milky while showing carbondioxide is present. Result: As the limewater changed colour it is proved that the plant gave off carbon dioxide during respiration. Interpretation: In A, soda lime (Potassium hydroxide) absorbs the carbon dioxide from the incoming air; the lime water in B should stay clear and prove that carbondioxide is absent from the air going into vessel C so that there is only the plant to give out carbobn dioxide to turn the lime water milky. 12 P a g e
3. Glycogen is stored in the arm muscles. How is energy released from this glycogen? Ans: The glycogen is converted into glucose by the action of glucagon and the aid of adrenalin. Glucose is oxidised or broken down to produse energy and other waste products, by the process respiration. If aerobic respirationm occurs, oxygen reacts with glucose to produce carbon dioxide water and a huge amount of energy. (2898 kj) Glucose + Oxygen Carbondioxide + Water + Energy If its oxygen supply limits or oxygen debt occurs, it respires anaerobically to produce lactic acid and a small amount of energy. Glucose Lactic acid + Energy (210 kj) 4 (a)(i) Describe an experiment which would show that rats release carbon dioxide. Your accounts should include a diagram of the apparatus used and description of a suitable control. Ans: Same as the previous question Q 2b. Only use a rat in flask C. [12marks] (ii). How much you alter the apparatus used in a (i) to show that a green plant release carbon dioxide? [1mark] Ans: Instead of flask C, a bell jar can be used which should be covered by a black paper to prevent photosynthesis. 5 (a) Humans use living organisms in a number of ways that are of economical importance. Describe the biological principles involved in each of the followings. (a) Yeast in baking and brewing. [4mark] Ans: Dough made of flour and water is mixed with yeast, which respire anaerobically to produce carbon dioxide and ethanol. The carbon dioxide causes dough to rise, making cavities appear in the bread. The ethanol evaporates during baking and the yeast is killed. During brewing or making beer, yeast is dissolved in a warm liquid containing the sugar maltose. The maltose comes from germinating barley seeds. The yeast respires, breaking down the maltose and making alcohol and carbon dioxide. The carbon dioxide makes the beer fizzy. 6 (a) Explain the causes of the changes that may occur in the blood as it passes through each of the following structures of a recently fed human. (i) An exercising muscle Ans: Each villus contains a dense network of minute thin-walled blood vessels or capillaries. The small molecules of the digested food, principally amino acids, and glucose, mineral salts and vitamins pass through the epithelium and the capillary walls by simple diffusion and active transport. As a result the glucose concentration of the blood increases while the osmotic potential decreases. The oxygen that the muscles need is carried by the blood from the alveoli of the lungs through systemic calculation. In an exercising muscle, cells need a lot of energy very quickly. To provide this energy the mitochondria in the muscles will be combining oxygen with glucose as fast as they can, to make ATP which will provide energy for the muscles by respiring aerobically at first. The heart also starts to beat faster so that oxygen can be brought faster to muscles by blood circulation. 7. Using named examples wherever possible, explain how humans use the activities of other living organisms in each of the following processes. (b) Brewing and baking. Ans: Same as the previous 5a. [4marks] 13 P a g e
8 (i) Name and describe the process in mammals which produces lactic acid. [3marks] Ans: The process is anaerobic respiration. In an exercising muscle, cells need a lot of energy very quickly. To provide this energy the mitochondria in the muscle cells will be combining oxygen with glucose as fast as they can during aerobic first. To supply more energy anaerobic respiration occurs in the muscle. A lot of lactic acid and less amount of energy is produced during anaerobic respiration. Glucose Lactic acid + Energy (210 kj) (iii) Describe how the body will break down lactic acid. [2marks] Ans: Lactic acid that is produced during anaerobic respiration in the body break down by the in taking of oxygen. For every 10g of lactic acid accumulated in the body 1.7 liters of oxygen must be absorbed. This oxygen is used in aerobic respiration to break down about one-sixth of the lactic acid into CO 2 and water, and this releases enough energy to convert the remaining five-sixth back into glucose. 9 Describe an experiment you could carry out to show that germinating seeds release heat energy. (6 marks) Ans: Apparatus: 2 vacuum flasks, 2 thermometers, some dead and germinating seeds and cotton wool. Procedure: Some seeds are soaked in water for 24 hours and half of them are killed by boiling for 10 minutes and then cooled. All seeds are added with a little disinfected solution. The dead seeds are placed in flask A and living seeds are placed in flask B. The thermometers are placed in such a way that its bulb is completely surrounded by seeds and its stems supported by cotton wool. The flasks are inverted upside down and left for few days. Observation: After a few days the temperature in flask B will be higher than in flask A. Result: Germinating seeds release energy during respiration. Interpretation: (i) Seeds are soaked in water so that they begin to germinate. (ii) The disinfected solution kills any microorganisms present. (iii) The cotton wool helps to insulate the apparatus, support the seeds, oxygen to diffuse in and carbon dioxide to diffuse out. (iv) The flask are inverted so that the thermometers need not to be inserted too deeply into flask and they can be read easily. Control: Flask A serves as a control. 14 P a g e
10 (a) Distinguish between respiration and breathing. (2 marks) Respiration Breathing It is a chemical process. It is a muscular process. O 2 is not always involved. O 2 is always involved. Releases energy. No energy released. 11 State 3 ways in which aerobic respiration differs from anaerobic respiration in mammals. (3 marks) Aerobic Respiration Anaerobic Respiration Oxygen is involved. Oxygen is not involved. Large amount of energy produced. Small amount of energy produced. CO 2 is always produced. CO 2 is sometimes produced. 11(a)(i) What is meant by the term anaerobic? Ans: Anaerobic means a type of respiration where oxygen is not required. 12(ii) Name the waste products from anaerobic respiration in yeast. Ans: The waste products are: Ethanol or alcohol and Carbon dioxide. 13(a)(iii) Name the waste products from anaerobic respiration in mammals. Ans: The waste products are: Lactic acid and carbon dioxide. 14(a)(i) Give a balanced equation for aerobic respiration. Ans: 6O 2 + C 6 H 12 O 6 6CO 2 +6H 2 O + 289 KJ of energy. 15(a)(ii) Name the products of anaerobic respiration in human and yeast. Ans: The products in human are: Lactic acid and comparatively small amount of energy. The products in yeast are: Ethanol or alcohol and small amount of energy. (1 mark) (1 mark) (1 mark) (3 marks) (3 marks) 16 Give 2 differences, other than the product, between aerobic and anaerobic respiration in human. ( 2 marks) Aerobic Anaerobic It involves carbon dioxide. It does not involve CO 2. During this reaction glucose is completely broken down. During this reaction glucose is partially broken down. 15 P a g e
17 Describe an experiment which shows that yeast produces CO2. (6 marks) Ans: 16 P a g e
18 Describe a controlled experiment you could carry out to show that germinating seeds carry out respiration. [6 marks] Note: In the answer use the figure given. But in flask C, use germinating seeds instead of the frog. Others same. 19 (c) Explain how each of the following obtains oxygen. (i) A human (ii) A leguminous plant [8marks] [6marks] Ans: (i) Before breathing in, diaphragm muscles contract and cause it to flatten from its original dome shape. The internal intercostal muscles also contract while external one relaxes, hence lower ribs are raised upwards and outwards. Accordingly sternum moves up and further away from backbone. These changes increase the volume of thorax and its dorsoventral diameter, and thus reduce air pressure in lungs. Thus air containing oxygen rushes into the lungs from atmosphere due to high atmospheric pressure by inspiration. The air at first passes through the nose or mouth. Inside the nose, the ciliated epithelium and film of mucus, which line the nasal passages helps to trap dust and bacteria. The air is slightly warmed before it enters the lungs through the trachea, bronchi, bronchioles and alveoli respectively. The outer surfaces of the alveoli are surrounded by single celled thick capillary network. Red blood cells moving through the capillaries absorb oxygen from the alveoli to form oxyhaemoglobin by diffusion. These oxygen molecules are transported through the blood circulatory system and are supplied to the body cells. Exchange of oxygen and carbondioxide takes place between body cells and blood capillaries also by diffusion. (ii) Plants have quite a large surface in comparison to their volume. Therefore, diffusion alone can supply all their cells with as much oxygen as they need for respiration. Diffusion occurs in leaves, stems and roots of plants. Leaves: During daytime leaves are photosynthesizing. This supplies plenty of oxygen for respiration. At night some oxygen diffuses into the leaves through the stomata. It dissolves in the thin layer of moisture around the cells and diffuses in across their cell walls and membranes. Stem: Soft stems also have stomata. Woody stems are covered with a layer of cork cells which make up the bark. These cells will not let air through, so the cork cells are packed loosely in places, to let oxygen diffuse into the cells underneath. These places are called lenticels. Roots: For tissue respiration, roots get their oxygen from the air spaces in the soil. If the soil is waterlogged for very long, they become short of oxygen. Under these conditions the roots will respire anaerobically, producing alcohol. This may kill the plant. 17 P a g e
20 (b) In flowering plants, explain how water is involved in each of the following: (i) The exchange of gases in the leaves. [2marks] Ans: The exchange of gases in leaves occurs through the spongy mesophyll cells. These cells are adapted for the diffusion of gases by having thin moisture lining outside them. The moisture lining allows gases to diffuse in and out easily. Also water make guard cells turgid to keep the stomata open. 21 (i) State four features common to gas exchange surfaces of flowering plants and mammals. [4marks] Ans: The 4 common features are: They have a large surface are to expose as much of them as possible to gases. They are thin to allow gases to diffuse as quickly as possible. They are moist for gases to diffuse in solution. They have efficient transport system to carry gases. 22(a)(ii) Explain how the gas exchange surfaces of a mammal functions more effectively than that of a flowering plant. [3marks] Ans: Mammals lungs are well ventilated to supply enough gas for respiration but flowering plants may reach a compensation point when there is no net gas exchange. Mammals can intake oxygen all the time through the life but plants can intake only in day time when the stomata are open. Humidity has no effect on human gas exchange but can effect plants gas exchange. 23(b) Give the function of intercostals muscles and describe how it performs its function. [4marks] Ans: There are two types of intercostal muscle: external and internal. During inspiration or breathing in, the external intercostal muscles contract while the internal one relax. As a result the ribs moves or swing upwards and outwards. Accordingly diaphragm flattens to increase volume of the thoracic cavity, pressure decrease. Atmospheric pressure forces air into them through nose and trachea. During expiration external intercostal muscles along with diaphragm relax to bring back everything, increased to their own position. Hence thorax pressure increases to squeeze air out of body. Sometimes we breathe out more forcefully - when coughing for example. Then the internal intercostal muscles contract strongly to make rib cage drop even further. The muscles of abdomen also contract, helping to squeeze extra air out of the thorax. 24 (a) (i) How is air pumped from the atmosphere into the alveoli in the lungs of a mammal? [10marks] Ans: When the level of CO 2 increases in the blood, the brain receives message from the carotid artery and send impulse to the intercostal muscle and diaphragm muscle. Before breathing in, diaphragm muscles contract and cause it to flatten from its original dome shape. The internal intercostal muscles also contract while external one relaxes, hence lower ribs are raised upwards and outwards. Accordingly sternum moves up and further away from backbone. These changes increase the volume of thorax and its dorsoventral diameter, and thus reduce air pressure in lungs. Thus air containing oxygen rushes into the lungs from atmosphere due to high atmospheric pressure by inspiration. The air at first passes through the nose or mouth. Inside the nose, the ciliated epithelium and film of mucus, which line the nasal passages helps to trap dust and bacteria. The air is slightly warmed before it enters the lungs through the trachea, bronchi, bronchioles and alveoli respectively. 18 P a g e
25 a (ii) Draw and label a diagram which shows the structure of a mammalian alveolus and its surrounding blood vessels. [5marks] 26 (a) (iii) Describe the absorption of oxygen in the alveolus and its transport from the alveolus in a mammal. [5marks] Ans: The outer surfaces of the alveoli are surrounded by single celled thick capillary network. Air taken into lungs during inspiration contains little carbon dioxide but more oxygen. Oxygen in alveolar cavity dissolve in film of moisture lining the alveoli and diffuse through the epithelium, capillary wall, the plasma and into a red cell. It combines loosely with haemoglobin to form an unstable compound called oxyhaemoglobin. The reaction can be shown as: Hb + 4O2 HbO8 19 P a g e
These oxygen molecules are transported through the blood circulatory system and are supplied to the body cells. ( From the alveoli oxygen is transported to the left atrium of the heart through the pulmonary veins. Contraction of left atrium passes blood to the left ventricle through bicuspid valves. The muscular contraction of the left ventricle forces blood through the aorta and aorta supplies blood to all the tissues of the body. ) Exchange of oxygen and carbondioxide takes place between body cells and blood capillaries also by diffusion. When it reaches a tissue, which needs oxygen, the oxyhb gives up its oxygen to form Hb again. Thus oxygen set free diffuses in solution into tissue cells. (** Write the italic lines within the first bracket is the ans. is for 8-10 marks.) 27 (a) Distinguish between respiration and breathing- [2marks] Ans: Respiration Breathing It is a chemical process. It is a muscular process. O 2 is not always involved e.g. yeast. O 2 is always involved. Releases energy. No energy released. 28 (c)(i) Explain how air is brought from the surroundings to the gas exchange surfaces of a human. [10marks] 29 (d) Describe how waste carbon dioxide is brought from a kidney cell to the gas exchange surfaces of a human. [7marks] Ans: The carbon dioxide made in the kidney cell during tissue respiration is diffused into the blood passing through it through capillary walls. It dissolves in water of red cells to form carbonic acid. The reaction is catalysed by enzymes, carbonic anhydrous. The carbonic acid is converted into hydrogen carbonate in red cells. Much of the hydrogen carbonate move out of red cells into plasma. A small amount is carried by Hb in red cells and some forms sodium hydrogen carbonate in plasma. The blood then flows through renal vein and vena cava to the heart, then to lungs through pulmonary arteries. When the blood passes through an alveolus where carbondioxide content is low, the carbonic anhydrous catalyse the reverse reaction and the hydrogen carbonates are converted to carbon dioxide and water. The carbon dioxide then diffuses out of the blood into alveolar cavities for exhalation. 30 Describe how carbon dioxide produced in a liver cell of a mammal is transported to the alveoli. [8 marks] Ans: The carbon dioxide made in the liver cells during tissue respiration is diffused into the blood passing through it through capillary walls. It dissolves in water of red cells to form carbonic acid. The reaction is catalysed by enzymes, carbonic anhydrous. The carbonic acid is converted into hydrogen carbonate in red cells. Much of the hydrogen carbonate moves out of red cells into plasma. A small amount is carried by Hb in red cells and some forms sodium hydrogen carbonate in plasma. The blood then flows through renal vein and vena cava to the heart, then to lungs through pulmonary arteries. When the blood passes through an alveolus where carbon dioxide content is low, the carbonic anhydrous catalyse the reverse reaction and the hydrogen carbonates are converted to carbon dioxide and water. The carbon dioxide then diffuses out of the blood into alveolar cavities for exhalation. 20 P a g e
31 (b) (ii) Describe an experiment you could do to show that a mammal breathes out more carbon dioxide than it breathes in. [5 marks] Procedure: The apparatus is set according to the figure shown. Lime water is poured taken into both flasks so that they are nearly half filled. T tube is placed in the mouth and normal breathing in and out is maintained. T A B Observation: The air enters the apparatus through one flask and leave by another. After a few breaths the lime water in tube A turns milky while that in B remains clear. Result: The exhaled (breaths out) air contains more carbon dioxide than in inhaled (breaths in) air. 32 (b) (i) Describe the process by which human take in air from their surrounding and pass it into their alveoli. [8 marks] 33(b) (ii) Humans may inhale soot particles from the atmosphere. Describe how those are trapped and expelled before reaching the alveoli. [3 marks] Ans: Soot particles may enter through nose and mouth from the environment. Some of them are trapped in the nose within the hairs. Tiny particles are trapped in the mucus secreted from the goblet cells present on the inner walls of trachea. The inner lining of the trachea is covered with ciliated cells. These cilia beat the mucus along with dust particles towards the pharynx, where these can be thrown out as spit or can be swallowed. The acidic environment inside the stomach can destroy them and make them harmless. 34 In humans, oxygen passes from the alveoli to the blood circulatory system. In amoeba oxygen passes from water into the cytoplasm. Give two ways in which the transfer of oxygen is similar in these organism, and two ways in which the transfer of oxygen in different. [4 marks] Ans: Similarities are- The process is diffusion Oxygen molecules stay in dissolve condition. Differences are: In human oxygen molecules are transported through blood but in amoeba oxygen molecules are absorbed from water directly. In human oxygen molecules are transported by the help of haemoglobin but in amoeba haemoglobin is absent. 35 (d) Name one gaseous pollutant of the atmosphere and state its precise effect on humans. [2marks] Ans: Gaseous pollutant is carbon mono oxide. It reduces the ability of bond formation between oxygen molecules and haemoglobin. 21 P a g e
36 (b) (i) Describes how substances are exchanged between air and blood at an alveolus [5 marks] Ans: The outer surfaces of the alveoli are surrounded by single celled thick capillary network. Air taken into lungs during inspiration contains little carbon dioxide but more oxygen. Oxygen in alveolar cavity dissolve in film of moisture lining the alveoli and diffuse through the epithelium, capillary wall, the plasma and into a red cell. It combines loosely with haemoglobin to form an unstable compound called oxyhaemoglobin. The reaction can be shown as: Hb + 4O 2 HbO 8 These oxygen molecules are transported through the blood circulatory system and are supplied to the body cells. 37 (b) Name the three type of air passage which carries air into the lungs [3 marks] ans: Nostril, nasal cavity, mouth, pharynx, trachea, bronchus, bronchioles etc.(use any three) 38 (c) In a healthy lung, mucus is produced and this trap bacteria is then moved out of the lungs and into the esophagus. (i) How is the mucus moved? [1 mark] Ans: By the ciliary beating. (ii) Describe what happens to the bacteria after they have been moved into the esophagus. [2 marks] Ans: The bacteria are swallowed and are taken to the stomach. The acidic environment inside the stomach can destroy them and make them harmless. 39 (b) Describe the mechanism by which carbon dioxide in the blood capillaries around the alveoli passes into the alveoli and exhaled [10 marks] 40 (c)(i) Name the two processes that occurs in the leaf of the flowering plant which involve gas exchange [2 marks] 22 P a g e
41 (c) Explain how the alveoli in a mammal are adapted for the function of gas exchange? [5 marks] Ans: The adaptations are that- 1. They have a large surface are to expose as much of them as possible to gases. 2. They are thin to allow gases to diffuse as quickly as possible. 3. They are moist, especially the inner wall where gases can be dissolved in solution. 4. They have an excellent transport system where blood capillaries from pulmonary arterioles surround the alveoli to absorb oxygen by red blood cells. 5. They have a good supply of oxygen, supplied by the respiratory system which are always kept open for air to enter. 42 (d) Gas exchange in a leaf can be affected by the environmental conditions surrounding the leaves. Explain how each of the following changes would affect the gases passing into and out of the leaf. i. An increase in light intensity. ii. An increase in temperature. [3+3=6 marks] 43 (c) (i) The lungs are excretory organs in mammals. Describe how lungs are inflated when breathing in. [7 marks] (ii) Describe how alveoli are adapted for gas exchange. Explain how each feature you give makes the process more efficient. [5 marks] 23 P a g e