The amoeba is a single-celled aquaticorganism whose entire body surface is always in contact with thesurrounding water. The organism is small and has a large surfacearea exposed to its aquatic environment. It therefore does not needan elaborate gaseous exchange system since its gaseous exchangecan be adequately met AUTHOR membrane. Oxygen dissolved in the surrounding water, diffuses across themembrane into the cytoplasm. In a similar manner, carbon IV oxide and other soluble wastes diffuses out through themembrane into the surrounding water along a concentrationgradient as illustrated in figure 2.6. Fig. 2.6: Gaseous exchange in an amoebaGaseous Exchange in InsectsInsects are generally small animals. The small size is quiteadvantageous to the animal in terms of gaseous exchange sincesurface area to volume ratio remains large. However, being largerthan amoeba, there is need for the development of a breathingsystem. This system is made up of a large network of air tubes thatform a tracheal system. The system penetrates into all parts of thebody to improve on the efficiency of gaseous exchange. Figure 2.7shows the tracheal system of a grasshopper. Fig. 2.7: The tracheal system of an insectThe tracheal system of an insect which forms its breathing systemconsists of spiracles and tracheolesSpiracles are external openings present on either side of theabdomen and thorax of an insect through which air from theatmosphere enters the body. Each spiracle is supplied with amuscular valve, that controls its opening and closing, and also withhairs to prevent excessive loss of water from the body tissues byevaporation. The spiracles then open into large tracheal tubes called tracheawhich are arranged in definite pattern and penetrate the wholebody space of an insect. These air tubes are reinforced with spiralbands of chitin to keep them open. The trachea then subdivide intofiner air tubes called tracheoles, which ramify the body tissue of theanimal for direct supply of individual cells with oxygen. Since thetracheoles lack the spiral bands of chitin, they permit gaseousexchange across their thin moist walls. See figure 2.8.Fig.


The trachea then subdivide intofiner air tubes called tracheoles, which ramify the body tissue of theanimal for direct supply of individual cells with oxygen. Since thetracheoles lack the spiral bands of chitin, they permit gaseousexchange across their thin moist walls. See figure 2.8.Fig. 2.8: The branching of the tracheaMechanism of NAME in theTracheal System of an InsectAir is drawn into and out of the tracheal system AUTHOR wall. In wasps and bees, abdominalsegments are moved in and out length-wise, while in locusts andcockroaches the segments are moved laterally. When spiracle valves are open, air is drawn into the trachealsystem. After that the valves close and air is forced along thesystem AUTHOR diffuses into the tissuefluid and into the cells due to a higher oxygen diffusion gradient. Likewise carbon IV oxide diffuses out of tissue cells and into fluidsthen into the tracheal system due to a carbon IV oxide diffusiongradient as shown in figure 2.8.The thoracic spiracle valves close as the abdominal spiraclevalves open and the gas is released through the spiracle openingsin the abdomen of the insect. Insects which live in water also carry out gaseous exchange inwater. Insects such as the dragon fly or may fly larvae nymphs usetracheal gills that are seen as paired plates on either side of theabdomen as shown in figure 2.9.Fig.2.9: Position of may fly nymph tracheal gills However, most of the aquatic insects have an elaboratetracheal system and are not truly aquatic because they need tocome to the surface to breathe. For example, mosquito larvae havetheir spiracles near the rectum carried on a tube called respiratorysiphon. This siphon is opened when the larva comes to the surfaceof the water to take in air and is closed AUTHOR Larvae come to the surface of water periodically tobreathe and position themselves as seen in figure 2.10 a .


For example, mosquito larvae havetheir spiracles near the rectum carried on a tube called respiratorysiphon. This siphon is opened when the larva comes to the surfaceof the water to take in air and is closed AUTHOR Larvae come to the surface of water periodically tobreathe and position themselves as seen in figure 2.10 a . In thepupa stage, a pair of siphons open just behind the head piercethrough the water surface to allow for gaseous exchange as shownin figure 2.10 b .Fig.2.10 a : The breathing structures of a mosquito larvaSome adult insects like water beetles and water bugs use bubblesof air trapped AUTHOR on their body surfaces. The air bubbles give these insects a silvery appearance. But likemost other aquatic animals, they first come to the surface toreplenish their stock of air. However, others still use the respiratorydevice, plastron for gaseous exchange. The plastron is a pile ofvery fine non-washable hairs which cover the cuticle for somedistance around the spiracle to hold off water and also to maintaina film of air over the body surface. Fig.2.10 b : The breathing structures of a mosquito pupaPractical Activity 3Observation of breathing movements of an insectRequirementsLive specimens of grasshopper locust cockroach, boiling tube andhand lens. Procedure1. Place the insect in a boiling tube and close.2. Using a hand lens observe the insect in the boiling tube. Recordthe observation and variations of the abdominal movements andspiracles of the insect.3. Remove the insect, hold it AUTHOR the hand lensobserve the abdominal side. Study Questions7. Count and record the number of spiracles on the abdomen ofthe insect used in practical activity 3.8. Draw the abdomen and show the position and shape of thespiracles. NAME in a fishFish live in water in that contains oxygen and other gases aredissolved in it. The breathing system of a bony fish consists of themouth or buccal cavity, gills, opercular cavity and the operculum. See figure 2.11 a . Fig.


Draw the abdomen and show the position and shape of thespiracles. NAME in a fishFish live in water in that contains oxygen and other gases aredissolved in it. The breathing system of a bony fish consists of themouth or buccal cavity, gills, opercular cavity and the operculum. See figure 2.11 a . Fig. 2.11 a : The position of the gills in a bony fishThe gills of a fish consist of a long curved bony structure calledgill bar. It is from the gill bar that most gill filaments arise. The gillfilaments trail in water to provide a large surface area for gaseousexchange. When a fish is lifted out of water, the surface tensioncauses the gill filaments to clump together thus reducing theeffective area of the respiratory surface. Arising from the other sideof the gill bar facing the mouth are the gill rakers. These appearas teeth-like structures whose function is to prevent food and anysolids present in water from reaching the delicate gill filaments. Theblood vessels from the body enter into the gill bar and branch intothe gill filaments as blood capillaries. These delicate structures areprotected in the bony fish AUTHOR on either side ofthe body near the head known as the operculum. See figure2.11 b .Fig. 2.11 b : A gill of a fishMechanism of NAME in the NAME FishThe floor of the mouth cavity is lowered AUTHOR of the floor of the mouth increases thevolume of the mouth cavity but reduces the pressure. As a resultwater flows into the mouth through the open cavity. Meanwhileeach closed operculum on either side of the mouth bulges outwardsto cause reduction of pressure in the gill cavity so that watercontaining dissolved oxygen then flows from the mouth cavity to thegill chamber over the gills. See figure 2.12.Fig. 2.12: Movement of water over gillsWhen all this is happening, the higher external pressurepresses the flexible free edge of each operculum against the side ofthe mouth of the fish. Each operculum in this case acts as a valve toensure that water enters only through the mouth. The mouth thencloses and muscles raise the floor of the mouth cavity.


2.12: Movement of water over gillsWhen all this is happening, the higher external pressurepresses the flexible free edge of each operculum against the side ofthe mouth of the fish. Each operculum in this case acts as a valve toensure that water enters only through the mouth. The mouth thencloses and muscles raise the floor of the mouth cavity. This forcesthe remaining water in the mouth to flow towards the gill chamber. Water entering the mouth has a higher concentration of oxygenthan in the gill filaments. Due to this difference, oxygen diffusesfrom water flowing over the gills into the blood through the thinwalls of the blood capillaries. The oxygen absorbed then combineswith haemoglobin in the blood of the fish and is then transported toall parts of the body. On the other hand the carbon IV oxideconcentration in the blood capillaries of the gill filaments is higherthan that in water. This difference causes carbon IV oxide todiffuse out of the blood into the flowing water through the walls ofthe blood capillaries. To facilitate maximum gaseous exchange between the waterflowing over the gills and the blood in the gills, a steepconcentration gradient must be maintained across the respiratorysurface. For this reason, water and blood flow in opposite directionswithin the respiratory surface. This is the counter-current flowsystem. As the movement of blood and water continues in oppositedirections within the respiratory surface, oxygen diffuses out of thewater into the blood and carbon IV oxide from blood into water. AUTHOR leaves the respiratory surface, it has as muchoxygen as the water. This is so because as water moves along, lessand less oxygen diffuses out of it as blood becomes more and moreconcentrated with oxygen. See figure 2.13.Fig. 2.14. The counter current flow system across the gillsPractical Activity 4To examine the structure of a gillRequirementsFresh fish, scissors or scalpel, water in a beaker and handlens microscope. Procedure1. With a pair of scissors or scalpel cut out the operculum at thebase where it is attached to the body wall.2. Using the same pair of scissors or scalpel cut out a complete gillfrom the gill chamber.3. Put the gill in water.4. Observe and draw a complete gill. 5.


Put the gill in water.4. Observe and draw a complete gill. 5. Examine a gill filament using a hand lens or under the lowpower of a microscope. Study Questions9. Draw the structure of the gill filament from the observations youmade in practical activity 4.10. Suggest how the total surface area of the gills in a fish can beestimated. State the significance of a large surface area of thegills to the fish.11. How is the gill of a fish adapted to its function?Mechanisms of NAME inAmphibiansAmphibians AUTHOR land and in water. This doublehabitation calls for special adaptation in gaseous exchange. Theyachieve this AUTHOR of gaseous exchange. These are:1. Gaseous exchange through lining of the buccal cavity.2. Gaseous exchange through the lungs.3. Gaseous exchange through the skin. Since the amphibians have neither ribs nor diaphragm, themechanisms which causes ventilation cannot be the same as thosein mammals. Air is therefore forced into and out of the lungs AUTHOR The example of frog is used in this section as arepresentative of the amphibians. Buccal Mouth CavityAir is taken or expelled from the mouth cavity AUTHOR of the mouth. The lining of the mouth cavity ismoist and oxygen from the air dissolves in it. Under the linings ofthe mouth, there is a rich supply of blood capillaries and oxygendiffuses into the blood and is carried AUTHOR ofthe body. Carbon IV oxide from the tissues is brought AUTHOR cavity where it diffuses out. The LungsThe lungs lie in the body cavity of the amphibian. When the nostrilsare closed, the air can be forced into the lungs AUTHOR floor of the mouth. The air reaches the alveoli sacs ofthe lungs that are well supplied with blood through a large networkof blood capillaries. The oxygen in the air dissolves into the moistinner lining of the alveoli. It then diffuses into the blood across thewall of the capillaries, combines with haemoglobin in the red bloodcells and is transported to all parts of the body.


The air reaches the alveoli sacs ofthe lungs that are well supplied with blood through a large networkof blood capillaries. The oxygen in the air dissolves into the moistinner lining of the alveoli. It then diffuses into the blood across thewall of the capillaries, combines with haemoglobin in the red bloodcells and is transported to all parts of the body. The carbon IV oxide from the tissues is carried AUTHOR into thealveoli, then pumped out AUTHOR the mouthcavity. The SkinFrogs have a thinner and moist skin than the toads. Beneath theskin is a large network of blood capillaries. Oxygen from the air andfrom the water diffuses through the skin into the blood stream. Onthe other hand carbon IV oxide in the blood diffuses out of theblood capillaries through the moist skin into the surrounding waterand air. Toads do not use the skin surface for gaseous exchangenormally except when they are hibernating. See figure 2.15.Fig.2.15: The surfaces of gasesous exchange in frogMechanisms of NAME inMammalsBreathing system in mammals consists of the following structures:lungs, trachea, chest cavity made of ribs and intercostal muscles,diaphragm and nostrils or nose as shown in figure 2.16 on page 60.The human being is used as a representative of mammals. NoseThe nose has two openings called nostrils which let in air into theair passages. As air moves in the passages, it is warmed andmoistened. The lining of nasal cavity of the nose also houses thesense organs for smell. The LarynxThe larynx is also the voice box. It is located on top of the trachea. Its muscle fibres and the vocal cords control the pitch of the voice. TracheaThe trachea is a tube made up of rings of cartilage which ensurethat it does not collapse during breathing. The lumens of thetrachea are lined with ciliated epithelium. The cilia beat in wavesand move the mucus and foreign particles towards the pharynxaway from the lungs. As the trachea enters the lungs, it divides intotwo branches called bronchi singular bronchus .LungsLungs are found in the chest cavity.


The lumens of thetrachea are lined with ciliated epithelium. The cilia beat in wavesand move the mucus and foreign particles towards the pharynxaway from the lungs. As the trachea enters the lungs, it divides intotwo branches called bronchi singular bronchus .LungsLungs are found in the chest cavity. They are enclosed in a doublemembrane known as pleural membrane. One part of the membraneadheres tightly to the lungs and the other covers the inside of thethoracic cavity. The space between these membranes is known asthe pleural cavity. It is filled with pleural fluid which reduces frictionand therefore make the lungs move freely in the chest cavity duringbreathing. Fig. 2.16: The structure of the lung of a human beingWithin the lungs, each bronchus divides into small tubes calledbronchioles. The bronchioles branch and terminate in groups of tinyair sacs called alveoli singular alveolus hence the spongy nature ofthe lungs. The alveolus is covered AUTHOR bloodcapillaries as shown in figure 2.16 c on page 60. NAME 5To display the respiratory system of a mammalRequirementsFreshly killed rats or rabbits , dissecting board or tray, dissectingpins, scissors, scalpels, forceps, hand lens, cotton wool, water anddrinking straw. Procedure1. Dissect the mammal using the procedure in the dissecting guideand display the following: i trachea ii rib cage iii the bronchi iv the lungs v diaphragm. Study Questions12. Connect the straw to the trachea of the animal in practicalactivity 5 and carefully blow air into the trachea, notice whathappens to the lungs. Count the number of lobes on the lungs and note the number inyour note book.13. Draw and label the respiratory system of the animal in thedissection. NAME of NAME is accomplished AUTHOR air pressure ofthe thoracic cavity. The thoracic cavity is enclosed AUTHOR the vertebral column at the back and sternum in front. The ribs are covered AUTHOR , and below the cavity isthe diaphragm.


Connect the straw to the trachea of the animal in practicalactivity 5 and carefully blow air into the trachea, notice whathappens to the lungs. Count the number of lobes on the lungs and note the number inyour note book.13. Draw and label the respiratory system of the animal in thedissection. NAME of NAME is accomplished AUTHOR air pressure ofthe thoracic cavity. The thoracic cavity is enclosed AUTHOR the vertebral column at the back and sternum in front. The ribs are covered AUTHOR , and below the cavity isthe diaphragm. The diaphragm is a muscular sheet of tissueextending across the floor of the cavity between the thoracic cavityand abdomen. It curves upwards to form a dome shape. Breathing mechanism involves two processes: inspiration inhalation , and expiration exhalation . Inspiration is breathing in,and expiration is breathing out. These two processes are broughtabout AUTHOR and diaphragm. See figure 2.17 onpage 62.Inspiration InhalationThis process occurs when the thoracic cavity increases in volumeand therefore decreases in pressure. A number of movements areinvolved during the enlargement of the thoracic cavity. Duringinspiration the external intercostal muscles contract while theinternal intercostal muscles relax. This movement pulls the ribsupwards and outwards. The diaphragm, which is domeshapedflattens AUTHOR muscles. The flattening of thediaphragm together with the outward movement of the ribsincreases the volume of the thoracic cavity and decreases thepressure inside it. Atmospheric pressure being higher than pressureinside the thoracic cavity, forces air to rush into the lungs throughthe nose and trachea hence inflating the lungs. Figure 2.17 a summarises these movements. Expiration ExhalationThis process occurs when the volume of the thoracic cavitydecreases and the pressure inside it increases. This is broughtabout AUTHOR : the external intercostal muscles relax whilethe internal intercostal muscles contract bringing the ribs down totheir original position. At the same time the muscles of thediaphragm relax and it regains its original shape. These movementsdecrease the volume of the thoracic cavity and increase thepressure inside it. Thus air is forced out of the lungs through the airpassages into the atmosphere.


At the same time the muscles of thediaphragm relax and it regains its original shape. These movementsdecrease the volume of the thoracic cavity and increase thepressure inside it. Thus air is forced out of the lungs through the airpassages into the atmosphere. See figure 2.17 b for the summary. Epee, tomes nt nee Diopeagmrcine ondrenrs to donehapa dacs lame of orsDiaplesgnflaened crease line of raeFig. 2.17: Movement of ribs during breathingPractical Activity 6 a To investigate the movement of the lungs and diaphragm ina model thoracic cavityRequirementsTwo balloons, bell jar, rubber stopper with a hole, y-shapedconnector and rubber sheet. Procedure1. Set up the apparatus as shown in figure 2.18.Fig. 2.18: To investigate the rib action during breathing using a model2. Pull down the rubber sheet at the base of the bell jar.3. Observe what happens to the balloons.4. Release the rubber sheet slowly and observe what happens tothe balloons. Study Question14. In what ways is this model similar or dissimilar to the working ofthe thorax of a living mammal? NAME 6 b To investigate the rib action during breathing using a modelRequirementsPieces of timber hardboard, nails and a string. Procedure1. Loosely join up the pieces of timber as in figure 2.19. Ensurethat there is free movement where the timbers are joined. Fig. 2.19: Model illustrating the action intercostals muscle in moving ribs2. Tie pieces of string A and B at points X and X1 respectively.3. Make corresponding holes Y and Y1 on the cross timbers ribs so that the string can move at Y or Y1 when moved.4. Pull down string A at O1.5. Notice what happens to the ribs and the sternum.6. Now pull up string B at O1.7. Notice what happens to the ribs and the sternum.8. Record and explain the above observation. Exchange of Gases in the AlveolusThe alveoli and the blood capillaries are made of very thin walls. The wall of the alveolus is covered AUTHOR whichdissolves oxygen in the inhaled air.


Notice what happens to the ribs and the sternum.8. Record and explain the above observation. Exchange of Gases in the AlveolusThe alveoli and the blood capillaries are made of very thin walls. The wall of the alveolus is covered AUTHOR whichdissolves oxygen in the inhaled air. Since oxygen concentration inthe blood is lower than in the alveolus, it diffuses through theepithelium, the capillary wall, the plasma and into the red bloodcells where it combines with haemoglobin. Carbon IV oxide in thecapillaries surrounding the alveoli is at a higher concentration thaninside the alveoli. Hence it diffuses into the alveoli. See figure 2.20.Water vapour passes out of the blood AUTHOR 2.2 shows the estimated percentage of different gases in inhaledand exhaled air. Table 2.2: Percentage composition of gases in inhaled andexhaled airGas in inhaled air in exhaled airOxygen2016.9Carbon IV dioxide0.034.0Nitrogen and other gases79.9779.97Regulation of BreathingBreathing movements normally take place unconsciously. In thebrain there is a region called medulla oblongata which controlsbreathing movements. As the carbon IV oxide in the bloodreaches this region it triggers this part of the brain to send impulsesto the rib muscles and the diaphragm, which in turn respondappropriately. This makes breathing to continue on and on. Fig. 2.20: Gaseous exchange in the alveolusDuring vigorous activity the concentration of carbon IV oxideincreases in the body tissues. As a result of this, more carbon IV oxide diffuses into the blood and reaches the medulla oblongata. The high concentration of carbon IV oxide in blood triggers themedulla oblongata to increase the rate of breathing. Increased rateof breathing helps to increase the amount of oxygen in the bloodthereby meeting the demands of the increased tissue respiration. Factors affecting the rate of breathing inhumans1. ExerciseDuring vigorous physical activity the rate of breathing increases soas to meet the increased oxygen demand. Faster breathing alsoeliminates the extra carbon IV oxide produced AUTHOR 2. AgeYounger people have a higher demand for oxygen.


ExerciseDuring vigorous physical activity the rate of breathing increases soas to meet the increased oxygen demand. Faster breathing alsoeliminates the extra carbon IV oxide produced AUTHOR 2. AgeYounger people have a higher demand for oxygen. They thereforehave faster breathing rate.3. EmotionsGenerally the body emotions affect the production of hormoneadrenaline which increases the general metabolism and henceincreased rate of breathing. Examples include fear, anxiety andfright.4. TemperatureGenerally when the temperature is high there is a tendency in therate of gaseous exchange to increase. However, if the temperatureis too high the breathing rate will reduce.5. HealthOne effect of illness is fever. The temperature of the body tends toincrease hence increased metabolic rate, which leads to higher rateof breathing. Some respiratory diseases block the respiratory tractmaking breathing difficult. Study Question15. Suggest how altitude may affect the rate of breathing. Lung volumesLungs of an adult can hold approximately 5 500 cm3 of air whencompletely filled. This volume is known as lung capacity. Howeverthis volume is not reached normally. During normal breathing, asmall volume of air about 500 cm3 is taken in and out of the lungs. This volume of air is referred to as the tidal volume. A person is capable of having a forced inhalation in addition tothe tidal volume. This additional volume is called inspiratoryreserve volume and reaches about 2 000 cm3. The tidal volumeplus inspiratory reserve volume forms what is referred to asinspiratory capacity. After normal exhalation, it is possible toforce out extra volume of air. This volume is referred to asexpiratory reserve volume and can be up to 1 300 cm3. It is alsopossible to have the deepest possible exhalation. Such a volume ofair, which can only be forcibly pushed out of the lungs, is called thevital capacity. However, it is not possible to force all air out of the lungs evenafter the deepest exhalation. The air that normally remains in lungsis referred to as the residual volume and is about 1 500 cm3. Seefigure 2.21 for a graphical representation. Fig. 2.21: Lung volumes in a human beingPractical Activity 7Effect of exercise on the rate of breathingRequirementsStop watch wrist watch. Procedure1.


The air that normally remains in lungsis referred to as the residual volume and is about 1 500 cm3. Seefigure 2.21 for a graphical representation. Fig. 2.21: Lung volumes in a human beingPractical Activity 7Effect of exercise on the rate of breathingRequirementsStop watch wrist watch. Procedure1. Pair up, one of you to be the subject and the other to record.2. When the subject is relaxed and breathing normally, the partnerwill count the number of inhalations per minute.3. Repeat this for a period of three minutes and record in table2.3.4. The subject should run around the laboratory and come back tothe laboratory. Count the number of inhalations as before. Table 2.3: Effect of exercise on breathing InhalationsTime min Before exercise 1After exercise 2 3Study Question16. From your results explain the effect of exercise on the rate ofbreathing. NAME 8To compare the amount of carbon IV oxide in the inhaledand the exhaled airRequirementsTest-tubes, glass tubing, rubber tubing, corks, a T-shaped connectorand calcium hydroxide solution. Procedure1. Set up the apparatus as shown in figure 2.22.2. Controlling the breath, slowly breathe out through the mouthinto the mouth piece several times.3. Notice what happens to the solution in test-tubes A and B.4. Now breathe in slowly through the mouth AUTHOR A and B.5. Notice what happens to the solution in test-tubes A and B.Study Question17. Explain the changes in calcium hydroxide solution in the testtubes in practical activity 8.Diseases of the Respiratory SystemRespiratory diseases are those which affect the breathing structuresand make gaseous exchange in animals difficult. They include:1. AsthmaAsthma is a common respiratory disease caused by: i Allergy to the respiratory structure due to pollen grains,atmospheric dust, animal s fur, scents from certain drugs, foodsand flowers. Fig. 2.22: Set-up for comparing amounts of carbon dioxide taken in and out ii Lung or bronchial infections AUTHOR.


AsthmaAsthma is a common respiratory disease caused by: i Allergy to the respiratory structure due to pollen grains,atmospheric dust, animal s fur, scents from certain drugs, foodsand flowers. Fig. 2.22: Set-up for comparing amounts of carbon dioxide taken in and out ii Lung or bronchial infections AUTHOR problem comes in form of attacks which are mild orsevere. When the weather is cloudy and chilly, or exposure to the causativeagents listed in i above, the attacks are more frequent. Thepatient may have difficulty in breathing because of the constrictionof air channels caused AUTHOR ,therefore, produces a characteristic wheezing sound accompaniedby the feeling of suffocation. Treatment and ControlTreatment and control of asthma consist of: i The spraying of a muscle-relaxant directly into the bronchialtubes. Ii Injection of drugs or oral application of pills prescribed AUTHOR iii Avoiding the causative agents.2. BronchitisThis is an inflamation of the bronchial tubes. There are two types ofbronchitis, namely; acute bronchitis and chronic bronchitis. A Acute bronchitisThis is widespread illness in children and frail adults. It is causedby: i A complication of the common cold when one is exposed tolow temperatures especially in high attitudes. It results into thechilling of the body, giving way to bacterial infection. Ii A complication resulting from a previous disease attack forexample measles, dengue, whooping cough and influenza. Theclinical symptoms include: headache, mild fever and coughingthat are accompanied AUTHOR The illness may clear in a few days or may persist forseveral months. B Chronic BronchitisChronic bronchitis develops after several repeated attacks of acutebronchitis. It is a fatal condition which makes the sufferer disabledand unfit to work. Its symptoms are: i Production of phlegm thick sputum that is greenish oryellow in colour due to pus from respiratory surface. Ii The patient has difficulty in breathing and finds it difficult towalk or sleep unless propped up in bed to ensure that thebronchial tubes are not clogged. Treatment and ControlPatients should seek early medical assistance when the illness isstill in its early stage.3.


Theclinical symptoms include: headache, mild fever and coughingthat are accompanied AUTHOR The illness may clear in a few days or may persist forseveral months. B Chronic BronchitisChronic bronchitis develops after several repeated attacks of acutebronchitis. It is a fatal condition which makes the sufferer disabledand unfit to work. Its symptoms are: i Production of phlegm thick sputum that is greenish oryellow in colour due to pus from respiratory surface. Ii The patient has difficulty in breathing and finds it difficult towalk or sleep unless propped up in bed to ensure that thebronchial tubes are not clogged. Treatment and ControlPatients should seek early medical assistance when the illness isstill in its early stage.3. NAME cough results from acute infection of the respiratory tractby a bacterium called Bordetella pertussis. The disease is endemicin Kenya. The symptoms are: i Prolonged coughing and vomiting. Ii Conjunctival haemorrhage accompanied AUTHOR iii Severe bronchopneumonia. Iv Convulsions and coma. V Ulcers and cardiac failure or complications. Vi Malnutrition signs for protein and energy deficiency due torepeated vomiting with difficulty in feeding. Treatment i Complicated cases should be admitted to hospital forspecialised care and administration of antibiotics. Ii Patients should be fed on a balanced diet. Control: Children should be immunised at an early age.4. PneumoniaPneumonia is an inflammation of the lungs AUTHOR of pneumonia caused AUTHOR : i Lobar pneumonia caused AUTHOR attack of pneumonia occur after a short incubationperiod followed by: a coughing b fevers c chest pains and d deposits of fluid in the lungs. The invasion proceeds from the throat spreading to other parts ofthe body. This sets on when the patient s body is completelyweakened. TreatmentThe patient should use antibiotics which include penicillin andsulphonamides. Control i Avoid overcrowded places. Ii Provide good ventilation in living premises.5. Pulmonary TuberculosisTuberculosis is a respiratory disease caused AUTHOR.


This sets on when the patient s body is completelyweakened. TreatmentThe patient should use antibiotics which include penicillin andsulphonamides. Control i Avoid overcrowded places. Ii Provide good ventilation in living premises.5. Pulmonary TuberculosisTuberculosis is a respiratory disease caused AUTHOR It is airborne, but occasionally it isspread through infected cow s milk or other fluids taken as a meal. The symptoms include: i General weight loss. Ii Coughing, sometimes with sputum containing blood. Iii Slight afternoon fever. The bacterium destroys lung tissues making it hard for the patientto breathe. It may eventually result into death. Treatment involves use of antibiotics especially, streptomycin. Control i Detection of the disease in its early stages AUTHOR ii Pasteurisation of milk. Iii Vaccination of the population using BCG Bacille CalmetteGuerin .6. Lung CancerCancer is an uncontrolled cell growth in the body resulting intotissue tumour or enlargement. The tumour can be benign whichaffects cells at a single point or malignant when affected cellsbreak away and spread to other parts of the body .There are no specific causes for lung cancer but it may resultfrom: i Smoking, in which the mucal walls of the bronchial tubes areblocked with deposits of tar from the cigarette smoke. Tarcontains cancer-causing carcinogenic substances that cantrigger uncontrollable growth of the lung cells. Ii Inhalation of cancer-causing substances such as asbestos dustsor exposure to: a radiation e.g. X-ray, gamma rays, cosmic rays. B Radio-active substances e.g.


The tumour can be benign whichaffects cells at a single point or malignant when affected cellsbreak away and spread to other parts of the body .There are no specific causes for lung cancer but it may resultfrom: i Smoking, in which the mucal walls of the bronchial tubes areblocked with deposits of tar from the cigarette smoke. Tarcontains cancer-causing carcinogenic substances that cantrigger uncontrollable growth of the lung cells. Ii Inhalation of cancer-causing substances such as asbestos dustsor exposure to: a radiation e.g. X-ray, gamma rays, cosmic rays. B Radio-active substances e.g. uranium. C Substances that alter the genetic composition of a cell e.g.mustard gas, sulphur dioxide used as a preservative infoodstuff. Lung cancer destroys the lung cells and tissues and as a result thisinterferes with free exchange of respiratory gases, which mayeventually lead to death. TreatmentThis involves: i Surgery to remove the tumour. Ii Radiotherapy to destroy cancerous cells. Iii Chemotherapy to relieve the patient of pain and to destroy thecancer cells. Iv The combination of several drugs each toxic to cancer cellsenhances the treatment programme i and ii above. V AUTHOR passively and in foodpreservatives. Study Question18. Suggest how too much dust particles may affect therespiratory system. Revision Questions1. What is meant AUTHOR ? Name the gasesexchanged. 2. Explain why the respiratory surface has to be: a thin, b moist.3. Explain how the following are adapted to their functions. A Guard cell. B Aerenchyma tissue.4. List the environmental factors influencing the opening andclosing of stomata.5. State the advantages and disadvantages of having stomata oneither side of the leaves.6.


Explain how the following are adapted to their functions. A Guard cell. B Aerenchyma tissue.4. List the environmental factors influencing the opening andclosing of stomata.5. State the advantages and disadvantages of having stomata oneither side of the leaves.6. Samples of atmosphere and exhaled air were analysed AUTHOR oxygen and carbon IV oxide content. The following are the results, expressed in volumes perthousand. I Amount of oxygen in atmosphere 200. Ii Amount of oxygen in exhaled air 160. Iii Amount of carbon IV oxide in atmosphere 300. Iv Amount of carbon IV oxide in exhaled air 41.Explain the difference in volume of each gas between theatmosphere and the exhaled air.7. For each of the following animals, name the structures whichare the sites of gaseous exchange during breathing in: a Mammals, amphibians, and insects. B Explain the significance of branching of the tracheal systeminto fine tubes in an insect.8. A Compare the mechanism of gaseous exchange in an insectand a mammal. B Explain why a fish has to pass large amounts of watercontinuously over its gills during gaseous exchange.9. In an experiment to analyse a sample of air, a J-tube was usedto find out the amount of carbon IV oxide and oxygen in thesample. The length of the sample air in the J-tube was 8 cm andafter mixing it with some sodium hydroxide solution for someminutes, the length was reduced to 7.6 cm. When pyrogallic acidwas also made to mix with the sample of air for some minutes,the length reduced further to 6.6 cm. A What was the percentage of: i Oxygen? Ii Carbon IV oxide in the air sample? Show yourworking. B Explain the role of sodium hydroxide solution and pyrogallicacid in the experiment.10. In insects, a rare disease has been found to attack therespiratory system. Name the parts of an insect which are mostlikely to be damaged AUTHOR reason for youranswer.11.


In insects, a rare disease has been found to attack therespiratory system. Name the parts of an insect which are mostlikely to be damaged AUTHOR reason for youranswer.11. The following are events which take place during expiration in amammal. I The diaphragm and intercostal muscles relax. Ii The diaphragm returns to its original dome-shape. Iii The rib cage moves inwards. Iv The pressure in the thoracic cavity increases. A List the correct sequence of events which take place duringexpiration. B Explain what would happen to breathing in a mammal ifthe intercostal muscles were damaged AUTHOR 12. Figure 2.23 is intended to show a respiratory surface forgaseous exchange in a mammal. Suggest the corrections thatshould be made to the diagram before gaseous exchange cantake place. Fig. 2.2313. Figure 2.24 is an experiment set up to investigate gaseousexchange in living organisms. After every ten minutes each test-tube was gently shaken. A Name the test-tubes in which there will be a colour change. B Suggest the test-tube in which the indicator would changecolour fastest. Give reasons for your answer.14. A student divided a small air tight box into two chambers with awire mesh. In one chamber he kept a number of rats and in theother a number of potted plants. What was likely to happen ifthe box was placed in the dark for two hours? Explain youranswer.15. The apparatus in figure 2.25 can be used to demonstrate themechanism of breathing in a mammal. Fig. 2.24 a What structures in a mammal are represented AUTHOR : i The rubber balloon? Ii The syringe barrel? Iii The plunger? B If the plunger is pulled away from the balloon, what willhappen to the rubber balloon?Fig. 2.2516. In an experiment, the rate of gaseous exchange wasdetermined and recorded as shown in the table below. Usingthese figures, suggest which plant gaseous exchange structureswere responsible for these observed figures. Table 2.24StructureGaseous exchange in AApproximately 97BApproximately 2.5CApproximately 0.517.


2.2516. In an experiment, the rate of gaseous exchange wasdetermined and recorded as shown in the table below. Usingthese figures, suggest which plant gaseous exchange structureswere responsible for these observed figures. Table 2.24StructureGaseous exchange in AApproximately 97BApproximately 2.5CApproximately 0.517. In the year 2003 a new disease called NAME RespiratorySyndrome SARS emerged in China and within a short period oftime, it had killed people in Europe, America, Canada and Africa. It is mainly transmitted through air. I Name the organs that are likely to be infected. Ii What would be the easiest way of preventing the spread ofthe disease from one person to the other or country tocountry? CHAPTER THREERespiration3.1 IntroductionRespiration is the process AUTHOR chemicallybroken down in all living cells to release energy, carbon IV oxide,water or alcohol. Respiration takes place slowly and is controlled bymany different types of respiratory enzymes so that energy isproduced continuously and in small amounts. Respiration should not be confused with gaseous exchange. Notethat whereas respiration is a chemical process taking place insidetissue cells, gaseous exchange is a purely physical process whichtakes place at respiration surfaces. The term respiration asdescribed in this chapter is sometimes referred to as tissuerespiration or internal respiration. NAME 1To investigate what gas is given off when food is burntRequirementsAny of the following foods starch powder, crushed beans, maizeflour, milk powder .Test-tubes, calcium hydroxide solution, rubber stopper, anhydrouscobalt chloride paper, source of heat, delivery tube and retort stand. Procedure1. Place some food sample in a dry test-tube and insert a oneholed rubber stopper into the mouth of the test-tube.2. Hold the test-tube containing the food sample horizontally. 3. Pour a little calcium hydroxide solution into another test-tubeand support it.4. Using a delivery tube connect the two test-tubes ensuring thatthe free end of the delivery tube into the calcium hydroxide asillustrated in figure 3.1.Fig. 3.1: Set-up for investigating the gas given off when food is burnt5.


Pour a little calcium hydroxide solution into another test-tubeand support it.4. Using a delivery tube connect the two test-tubes ensuring thatthe free end of the delivery tube into the calcium hydroxide asillustrated in figure 3.1.Fig. 3.1: Set-up for investigating the gas given off when food is burnt5. Heat the test-tube containing the food sample strongly.6. Observe and record what happens to the food sample, calciumhydroxide solution and the upper sides of the test-tube with thefood sample.7. Disconnect the apparatus and rub anhydrous cobalt II chloridepaper on the inner upper side of the test-tube containing thefood sample.8. Record the colour change observed on the cobalt II chloridepaper. Study Question1. What conclusion can you draw from the above results ofpractical activity 1?Significance of NAME living organisms require energy all the time. The energy isobtained from food substances which are either taken in ormanufactured during photosynthesis. Examples of foods which canprovide large amounts of energy are carbohydrates like starch andglucose and fats. The energy derived from these food substancesas a result of respiration is used for such activities as muscularcontraction, conduction of nerve impulses, secretion of enzymes,growth, repair of worn out tissues, functioning of body organs suchas kidneys, heart and brain. However, some of the energy is alsolost in form of heat. Tissue respiration takes place mainly in cell organelles calledmitochondria. Structure and Function of a mitochondrionFig. 3.2: The structure of the mitochondrionMitochondria are small round or rod shaped cell organelles found incells and provide sites for respiratory activity. Living cells such asthe kidney cells, the flight muscle of insects and birds, the spermcells and muscle cells have high energy requirements andconsequently possess large numbers of mitochondria. The structure of mitochondria is shown in figure 3.2. It has twomembranes, the outer and inner membranes that are separated byfluid filled spaces. The inner membrane folds into projections insidethe matrix called cristae. The cristae provide a large surface areafor respiratory activities.


It has twomembranes, the outer and inner membranes that are separated byfluid filled spaces. The inner membrane folds into projections insidethe matrix called cristae. The cristae provide a large surface areafor respiratory activities. Enzymes are bound to the cristae. Types of NAME are two types of respiration namely aerobic and anaerobic. Aerobic RespirationAerobic respiration is the process in which food substances such asglucose are broken down in the presence of oxygen in tissue cells torelease energy, water and carbon IV oxide. The total energyreleased at the end of respiration oxidation is very high. If all theenergy were released at once in the form of heat, it would burn thebody cells. To protect the cells from burning the heat energy isreleased in small quantities in stages. This energy is used to bring about a chemical reaction in whicha compound in the cell called adenosine diphosphate ADP combines with an inorganic phosphate molecule to form anothercompound called adenosine triphosphate ATP . This reaction issummarised as follows:The following equation summarises the process of aerobicrespiration in plants and animals. Molecules of adenosine trisphosphate ATP store the energyreleased in respiration in their bonds and avails it to cells readilywhen required. The chemical equation as represented above gives the falseimpression that respiration involves only one chemical reaction. Thewhole process in fact involves a series of many reactions. A specificenzyme catalyses each of these reactions. In broad terms,respiration takes place in two major phases and each phase consistof a series of reactions. First phaseThe earliest stages of respiration take place without using oxygen. These stages involves a series of chemical reactions which occur inthe cytoplasm of the cell. A compound with a three-carbon moleculecalled pyruvic acid is formed from glucose. The breakdown ofglucose is called glycolysis. What happens after pyruvic acid isformed depends on whether oxygen is available for use or not. Ifoxygen is not supplied to the cell, then pyruvic acid is then partiallybroken down to lactic acid in animals or to ethyl alcohol ethanol and carbon IV oxide in plants. See chart below. In glycolysis, one molecule of glucose yields two molecules of ATP.Alcohol production occurs in plant tissues and duringfermentation AUTHOR.


What happens after pyruvic acid isformed depends on whether oxygen is available for use or not. Ifoxygen is not supplied to the cell, then pyruvic acid is then partiallybroken down to lactic acid in animals or to ethyl alcohol ethanol and carbon IV oxide in plants. See chart below. In glycolysis, one molecule of glucose yields two molecules of ATP.Alcohol production occurs in plant tissues and duringfermentation AUTHOR The alcohol accumulatesin these organisms provided oxygen is excluded. Second phaseThis phase takes place in the matrix of the mitochondria. It involvesa series of enzymecontrolled reactions that require oxygen. Thepyruvic acid formed in the first phase is further oxidised AUTHOR enzymatic reactions Kreb s cycle into carbon IV oxide, energy and water as the end products. In this reaction shown above, one molecule of glucose yields 38molecules of ATP.For the above process to be maintained in the living cells, thefollowing conditions are necessary: The cells must be provided with glucose or food. Oxygen must be taken in and react with the glucose. There must be respiratory enzymes to catalyse the reaction. Favourable temperature should be maintained for efficientenzyme functioning. The end products of the reaction i.e. carbon IV oxide, waterand energy must be constantly removed from the mitochondrion. NAME 2To investigate production of heat AUTHOR , soaked bean seeds, vacuum flasks, cotton wooland two thermometers, 10 formalin methanol and retort stand. Procedure1. Soak the seeds for 24 hours and then divide them into twoequal portions.2. Boil one portion of seeds for ten minutes, let them cool andwash them in 10 per cent formalin.3. Fill one vacuum flask with fresh not boiled seeds and the otherone with boiled seeds.4. Place a thermometer in each flask such that the bulb issurrounded AUTHOR 5. Hold each thermometer with cotton wool as shown in figure 3.3and record the initial temperature.6. Record the temperature every morning and evening for a week. Fig. 3.3: Set-up for investigating production of heat AUTHOR 2. What does production of heat in the germinating beans imply?3.


Record the temperature every morning and evening for a week. Fig. 3.3: Set-up for investigating production of heat AUTHOR 2. What does production of heat in the germinating beans imply?3. Explain AUTHOR in i above is produced. NAME in Plants and AnimalsAnaerobic respiration is the process AUTHOR glucose are broken down without using oxygen. It takes place inthe cytoplasm. The glucose is not broken down completely intocarbon IV oxide and water to release energy, as is the case ofaerobic respiration. Instead, an intermediate compound, alcohol inplants and lactic acid in animals, is produced. The incompletebreakdown of glucose result into production of less energy than incase of aerobic respiration breakdown of glucose is complete. Theprocess of anaerobic respiration is summarised as shown below. In the absence of oxygen, most plant and animal tissues can respireanaerobically for a limited period. It is essential, however, that theyget rid of the end products lactic acid in animals and in plantsethanol and carbon IV oxide immediately. This is because theseend products become toxic to the organism if they are left toaccumulate within the cells. Anaerobic respiration that results in the accumulation of alcoholis referred to as fermentation. Fermentation occurs when bacteriaor yeast break down simple sugars into energy, carbon IV oxideand alcohol. Some bacteria break down alcohol into ethanoic acidthrough anaerobic respiration. Similarly the break down of sugar inmilk AUTHOR production of energy and lactic acidwhich causes milk to become sour. NAME This is the oxygen required to get rid of the lactic acid thataccumulates in the body tissues when the supply of oxygen is lessthan the demand. Under these conditions, the animal tissues respirethrough anaerobic respiration and this causes lactic acid toaccumulate in the muscles. The lactic acid might cause fatigue andresult in muscle crumps. Another example of anaerobic respirationin animals is when a short distance runner or diver holds his or herbreath while running or diving. The oxygen debt incurred here is paid back AUTHOR quickly and more deeplyin order to increase the supply of oxygen during the recovery periodafter the race. Figure 3.4 shows a panting athelete.


Another example of anaerobic respirationin animals is when a short distance runner or diver holds his or herbreath while running or diving. The oxygen debt incurred here is paid back AUTHOR quickly and more deeplyin order to increase the supply of oxygen during the recovery periodafter the race. Figure 3.4 shows a panting athelete. Fig. 3.4: Oxygen debt in a panting athleteDuring the process of paying back the oxygen debt, the lacticacid is oxidised to carbon IV oxide, water and energy whenoxygen is available or it is taken to the liver and converted intoglycogen. Application of NAME inIndustries and at homeMan has applied the knowledge of anaerobic respiration in hiseveryday life for a long time with limited understanding of thephysiology of the process. Products of fermentation such as alcohol,wines, yoghurt and cheese are some of the examples. NAME ,bread baking industry uses yeast and so is the beer brewing anddistillery industry. Power alcohol used as a substitute for petrol isproduced through fermentation. The production of vinegar ethanoicacid citric acid, oxalic acid, butyric acids and some drugs alsodepends on fermentation. These chemicals are of great commercialvalue. The type of alcoholic drink produced AUTHOR nature of the sugar solution used. Forexample, fermentation of apple juice produces cider, grape juiceproduces wine, and malt extract from germinating barley producesbeer. Distillation of some of the products of fermentation gives riseto stronger alcoholic drinks called spirits. For example, distillingwine makes brandy. Other applications of anaerobic respiration include biogasproduction for cooking, lighting and making of compost manure. NAME 3To investigate the gas produced during fermentationRequirementsBoiling tube, measuring cylinder, test-tubes, thermometer, deliverytube, rubber stopper, 10 glucose solution, yeast, kerosene oil,retort stand and means of heating. Procedure1. Boil about 20 cm3 of glucose in a tube, cool to 40 OC add someyeast.2. Pour onto the glucose and yeast suspension some kerosene oil.3. Leave this for about one hour.4.


Boil about 20 cm3 of glucose in a tube, cool to 40 OC add someyeast.2. Pour onto the glucose and yeast suspension some kerosene oil.3. Leave this for about one hour.4. Put some calcium hydroxide in test-tube connect this test-tubeto the boiling tube using the delivery tube and rubber stopper. See figure 3.5. Fig. 3.5: FermentationStudy Questions4. Record the changes that occur in the calcium hydroxide and inthe boiling tube.5. What gas is produced?Aerobic and anaerobic respiration are similar because they bothproduce energy. However, they have various differences as shown intable 2.1. NAME and AnaerobicAerobic RespirationAnaerobic Respiration i Oxygen is necessary forthe process to take place. The use of oxygen ensuresa complete combustion oroxidation of the substrate. I Oxygen is not requiredhence the substrate is notbroken down completely. Ii High amounts of energyare released hence anefficient way of obtainingenergy. The amount ofenergy released from onemolecule of sugar is 2880KJ. 38 ATP molecules . Ii Low amounts of energyare released hence it is aninefficient method ofobtaining energy. Theamount of energyreleased from onemolecule of sugar is 210KJ. 2ATP molecules . Iii The substrate iscompletely broken down tocarbon IV oxide andwater. Iii The substrate is notcompletely broken downand as a result lactic acidor alcohol is produced. Iv The end products arewater and carbon IV oxide which diffuses out ofthe cells and is excretedbefore it accumulates inthe body to toxic levels. Iv The end products arealcohol in plants and lacticacid in animals. Both ofthese end-products aretoxic to cells accumulatein the body. V Water molecules areproduced. V Water molecules are notproduced. Vi Over a short period oftime, energy is notreleased faster. Vi Over a short period oftime, energy is releasedfaster. Respiratory SubstratesRespiratory substrates are energy-rich food substances which whenoxidised release energy e.g.


Theamount of energyreleased from onemolecule of sugar is 210KJ. 2ATP molecules . Iii The substrate iscompletely broken down tocarbon IV oxide andwater. Iii The substrate is notcompletely broken downand as a result lactic acidor alcohol is produced. Iv The end products arewater and carbon IV oxide which diffuses out ofthe cells and is excretedbefore it accumulates inthe body to toxic levels. Iv The end products arealcohol in plants and lacticacid in animals. Both ofthese end-products aretoxic to cells accumulatein the body. V Water molecules areproduced. V Water molecules are notproduced. Vi Over a short period oftime, energy is notreleased faster. Vi Over a short period oftime, energy is releasedfaster. Respiratory SubstratesRespiratory substrates are energy-rich food substances which whenoxidised release energy e.g. carbohydrates, fats and proteins. Carbohydrates are the main source of energy in respiration. These are mainly in the form of simple sugars such as glucose,fructose and galactose. They provide about 17 KJ per gram or 2 898KJ Mole when completely oxidised. Whereas plants synthesise their own food substances cellulose, starch and sugars , animals obtain most of these foodsubstances AUTHOR of the plant organs rich inthese food substances include maize, cassava, rice, fruits, yams,bananas, sweet potatoes, sugar cane and sorghum. Fats produce more energy than carbohydrates or proteins. When one gram of fat is completely oxidised it produces about 38KJ of energy. Plants synthesise fats and oils and store them inseeds, leaves and fruits. Some animals obtain them AUTHOR animal products. Plants that are rich in fats andoils include sesame, groundnuts, sunflower, coconut, cashew nutsand castor oil seeds. Some of the animal products rich in fatsinclude fatty meat, milk, ghee, cheese and butter. Fats are not themain substrates of respiration because they are not very solubleand therefore are not easily transported to the sites of respiration. It will also require more oxygen to oxidise one gram of fat than onegram of glucose. Proteins are not normally used in respiration.


Plants that are rich in fats andoils include sesame, groundnuts, sunflower, coconut, cashew nutsand castor oil seeds. Some of the animal products rich in fatsinclude fatty meat, milk, ghee, cheese and butter. Fats are not themain substrates of respiration because they are not very solubleand therefore are not easily transported to the sites of respiration. It will also require more oxygen to oxidise one gram of fat than onegram of glucose. Proteins are not normally used in respiration. However, inextreme cases of starvation the cells may use proteins to obtainenergy. Proteins are first broken into amino acids. Amino acids arethen deaminated broken down further and oxidised. One gram ofprotein produces 22 KJ when completely oxidised. Proteins aremainly found in plant leaves, seeds and fruits. Some of the plantsrich in proteins are beans, peas, sunflower, groundnuts, sesame andcashew nuts. Animals obtain proteins AUTHOR inproteins or on other animals or animal products such as lean meat,milk, eggs and cheese. NAME and its SignificanceRespiratory quotient RQ is a ratio showing the relationshipbetween the amount of carbon IV oxide used against the amountof oxygen used in respiration. Where carbohydrates such as sucrose and glucose are completelybroken down to carbon IV oxide, water and energy, the amount ofcarbon IV oxide produced almost balances the amount of oxygenconsumed. In this case of complete aerobic respiration of sugars,the RQ ratio is 1.0.The value of RQ varies with the type of substrates andconditions under which they are respired. RQ can therefore rangefrom less than one to more than one. The respiratory quotients givean indication of the type of substrate oxidised and whether aerobicrespiration, anaerobic respiration or both are taking place. For example, in respiration of fat the RQ is about 0.7. Thiswould mean that the amount of carbon IV oxide produced is lessthan the amount of oxygen used. RQ values for carbohydrates andproteins are 1.0 and 0.9 respectively. A value of less than oneindicates higher consumption of oxygen and lower production ofcarbon IV oxide. This would represent anaerobic respiration inwhich alcohol and carbon IV oxide are produced.


RQ values for carbohydrates andproteins are 1.0 and 0.9 respectively. A value of less than oneindicates higher consumption of oxygen and lower production ofcarbon IV oxide. This would represent anaerobic respiration inwhich alcohol and carbon IV oxide are produced. Respirationquotient also depends on age, temperature of the surrounding andstate of health of the organism. Factors affecting the rate of respirationFactors that affect the rate of respiration also affect the energyrequirements in organisms. Refer to chapter five of students bookone .Study Question6. State five factors that affect energy requirements in organisms. Other factors include:1. Oxygen ConcentrationRespiration is affected AUTHOR available in thetissues. When the amount of oxygen is low the rate of respirationslows down. When the amount of oxygen is high, the rate ofrespiration increases. In diving animals the oxygen concentration intheir environment is low. Hence, soon after they dive, the cardiacfrequency drastically decreases bradycardia and the arterioles ofall the vital body organs constrict so that oxygen can be deliveredto the vital organs that cannot endure oxygen deprivation e.g. thebrain and the heart. As a result of this, less oxygen reaches other body tissues andorgans hence their respiration rate reduces.2. Substrate concentrationThe primary respiratory substrate in the tissues is sugar. Whensugar concentration increases the rate of respiration also increases. The reverse is also true.3. HormonesCertain hormones in the body such as adrenaline and thyroxine areknown to increase respiratory activities.4. Surface area: Volume ratio Body size The surface area to volume ratio affects the rate of respiration. Ifthe surface area to volume ratio is high, the organism would losemore heat energy. As more energy is lost to the surrounding morewill be required to replace the lost energy hence higher rate ofrespiration. Revision Questions1. A Define the term respiration. B Distinguish between gaseous exchange respiration.2. Explain the significance of respiration in living organisms.3. A What is the role of mitochondrion in respiration? B State how the mitochondrion is structurally adapted to itsfunction.4. Explain the meaning of the following terms: i NAME RQ . Ii Oxygen debt. Iii Basal metabolic rate BMR . 5.


A What is the role of mitochondrion in respiration? B State how the mitochondrion is structurally adapted to itsfunction.4. Explain the meaning of the following terms: i NAME RQ . Ii Oxygen debt. Iii Basal metabolic rate BMR . 5. Describe what happens in the two phases of aerobic andrespiration.6. What is the economic importance of anaerobic respiration inindustry?7. A List the differences between aerobic and anaerobicrespiration. B What is the significance of anaerobic respiration? C Give examples of food in your community which provide uswith a lot of energy.8. Figure 3.6 illustrate an experiment on germinating peas. Fig. 3.6 a i What changes are observable at the end of theexperiment in figure 3.6 b ? Explain the change. Ii What chemical change is taking place in thegerminating peas? B If water had been used instead of potassium hydroxidesolution in the experiments, what would be observed?9. A student set up an experiment using soaked and dry seeds asshown in figure 3.7. Fig. 3.7 a State the objective of this experiment and the observationsmade after 24 hours. B Account for the observations made in a above. C Suggest why vacuum flasks were used in the experiment. D What alteration would you make in the set-up to make theresults more reliable?10. In an experiment on respiration, the rate of carbon IV oxideproduction in pea seedlings was recorded under differenttemperature, as shown in the table below. A Using the same axes, plot graphs to show carbon IV oxide production at each temperature against time. Let timebe on the horizontal axis. B What is the optimum respiration temperature for thisexperiment? Explain how the answer is arrived at. C Suggest reasons for the shape of the graph whentemperature was maintained at 40OC. CHAPTER FOURExcretion and Homeostasis4.1 IntroductionExcretion is a process AUTHOR andeliminate waste products formed during metabolic processes, fromtheir bodies. These waste products include carbon IV oxide,nitrogenous wastes, excess water, mineral salts, tannins, quinineand resins.


C Suggest reasons for the shape of the graph whentemperature was maintained at 40OC. CHAPTER FOURExcretion and Homeostasis4.1 IntroductionExcretion is a process AUTHOR andeliminate waste products formed during metabolic processes, fromtheir bodies. These waste products include carbon IV oxide,nitrogenous wastes, excess water, mineral salts, tannins, quinineand resins. If these substances were left to accumulate in the cellsor in the tissue fluid surrounding the cells, they would becomepoisonous or toxic to the cells. This would also alter the conditionsunder which cells function efficiently, leading to their death. It istherefore necessary to remove these waste products as quickly asthey are formed in order to provide a suitable working environmentfor the cells. A suitable working environment for cells can be established ifthe waste products and excess substances are kept at very low andnarrow ranges within and around the cells. Metabolic processesapart from producing these substances, release energy some ofwhich is in form of heat and therefore alter body temperature. Others, such as acidic and alkaline substances alter the pH of bodyfluids. All these factors have adverse effects on the metabolism ofthe body. Organisms therefore, have a self-adjusting mechanismcalled homeostasis that functions to maintain a steady state in theinternal environment of living organisms in order to provideoptimum conditions for body metabolism. Excretion, egestion and secretion are terms that denoteprocesses of releasing substances in or from the bodies of livingorganisms and therefore require to be understood. Egestion is aprocess that results in the removal of undigested materials fromfood vacuoles or alimentary canals of animals. The undigested foodmaterials which may not have entered into cells, to take part inmetabolism may be released as solid remains from the body. However, the digested food materials which enter the body tissuesare broken down. The waste products formed are removed from thebody AUTHOR hand, secretion is the release ofcertain useful substances produced AUTHOR , enzymes, oxalates, sebum and mucus. Plants and animals have various methods of disposing of wasteproducts and those methods involve diffusion and evaporation fromthe body. Excretion in PlantsPlants have not evolved complex organs for direct elimination oftheir wastes mainly because there is very little accumulation oftoxic wastes, for example, nitrogenous wastes.


The waste products formed are removed from thebody AUTHOR hand, secretion is the release ofcertain useful substances produced AUTHOR , enzymes, oxalates, sebum and mucus. Plants and animals have various methods of disposing of wasteproducts and those methods involve diffusion and evaporation fromthe body. Excretion in PlantsPlants have not evolved complex organs for direct elimination oftheir wastes mainly because there is very little accumulation oftoxic wastes, for example, nitrogenous wastes. Secondly, the mainwaste products are formed slowly from breakdown ofcarbohydrates. Often these wastes are reutilised AUTHOR include carbon IV oxide, oxygen and water. The gases are removed from the plant AUTHOR and lenticels. Some plants may store other wastes in their tissues, but in anon-toxic form. Some of these tissues or organs age and drop offfrom the plants for example leaves, flowers, fruits, and the bark. The substances stored include tannins, resins, calcium oxalate,calcium carbonate and alkaloids. Caffeine, nicotine, quinine andmorphine are examples of alkaloids stored in these tissues. NAME of Plant ExcretoryProductsTannins are deposited in dead tissues of wood and barks of treesfor example, acacia, mangrove and wattle tree. Commercially,tannin is used in treatment of leather. It combines with animalproteins to form a complex compound that is not easily brokendown AUTHOR tannin are also sprinkled onred-hot pots to give them their characteristic attractive colourpatterns. Caffeine is stored in coffee berries and tea leaves. It is takenas a mild stimulant that increases mental activity and reducesfatigue. Quinine is a waste product stored in the bark of cinchona treeand aloe leaves. Human beings use it for the treatment of malaria. Cocaine is obtained from leaves of coca plant. It is used as alocal anaesthetic. If taken in large quantities it causes greatphysical and mental defects and addiction. Cannabis is stored in fruits, flowers and leaves of Cannabissativa bhang . It is extracted and used in the manufacture ofdrugs. Nicotine is found in leaves of tobacco plants and is used inmanufacture of insecticides and narcotic drugs.


If taken in large quantities it causes greatphysical and mental defects and addiction. Cannabis is stored in fruits, flowers and leaves of Cannabissativa bhang . It is extracted and used in the manufacture ofdrugs. Nicotine is found in leaves of tobacco plants and is used inmanufacture of insecticides and narcotic drugs. Human beingssmoke it through cigarettes. Rubber is made from latex of rubber plant. It is used in shoeindustry. Sapodilla tree produces the type of latex that is used in themanufacture of chewing gum. Colchicine is an alkaloid derived from a plant that is used ingenetics in plant and animal breeding research and in cancertherapy. Gum arabica is an exudate from some varieties of acaciatrees, used in food processing and printing industry. Papain is obtained from raw pawpaw fruit skins. It contains aproteolytic substance used in food industry as a meat tenderiser. Khat from Khat edulis Miraa is chewed to act as a mildstimulant and used for medicinal purposes. CAUTION: Most of these plant products are many times misused inwhat is nowadays called drug abuse. In this, some of theseproducts such as khat, cocaine and cannabis are used without adoctors approval as stimulants. This behaviour is destructive toones health and is ill advised. Use of most of these substances inthe above mentioned manner is illegal in many countries. The samecase applies in trading in them. NAME 11. From the school surrounding locality find out those plants thatare of medicinal value.2. List any other economic importance of such plants. Excretion and Homeostasis in UnicellularOrganismsMost simple organisms such as protozoa live in aquaticenvironment. Their waste products include carbon IV oxide andnitrogenous wastes. Protozoa such as amoeba and paramecium depend on diffusionas a means of excretion. Their bodies have high surface area tovolume ratio that provide large surface area for gaseous exchangeand excretion to take place AUTHOR.


List any other economic importance of such plants. Excretion and Homeostasis in UnicellularOrganismsMost simple organisms such as protozoa live in aquaticenvironment. Their waste products include carbon IV oxide andnitrogenous wastes. Protozoa such as amoeba and paramecium depend on diffusionas a means of excretion. Their bodies have high surface area tovolume ratio that provide large surface area for gaseous exchangeand excretion to take place AUTHOR diffuse from cytoplasm, where they are at a highconcentration, across the cell membrane into the surrounding waterwhere their concentration is low. Another method of excretion is AUTHOR and paramecium live in an aquatic environment that ishypotonic to their body fluid, hence there is excess inflow of waterby osmosis. Excess water and dissolved chemicals accumulate inthe contractile vacuole. On reaching maximum size, a contractilevacuole moves to cell surface and bursts releasing the contents tothe surrounding. Soon afterwards, other contractile vacuoles form inthe cytoplasm accumulate more waste contents and the processcontinues. See figure 4.1 a , b and c . Fig. 4.1: Excretion in AmoebaExcretion in AnimalsExcretion in animals is carried out AUTHOR ofspecialised tissues and organs. This is because their bodies arecomplex and have greater number of cells, such that simplediffusion would not suffice as a method of excretion. The excretorytissues and organs include flame cells of platyhelminthes,nephridia of annelida, malpighian tubules of insects, gills,lungs, liver and kidneys of vertebrates. These organs are specialised to function in different environmentssuch as aquatic marine and fresh water and terrestrial. Excretion in NAME main excretory organs in mammals such as human beings arelungs, kidneys, skin and liver. These organs are discussed in greaterdetail in the sub-topics that follow this. Structure and function of mammalian skinThis is the largest body organ as it covers the whole body surfaceand even continues into many body openings like nostrils, mouthand ears.


This is because their bodies arecomplex and have greater number of cells, such that simplediffusion would not suffice as a method of excretion. The excretorytissues and organs include flame cells of platyhelminthes,nephridia of annelida, malpighian tubules of insects, gills,lungs, liver and kidneys of vertebrates. These organs are specialised to function in different environmentssuch as aquatic marine and fresh water and terrestrial. Excretion in NAME main excretory organs in mammals such as human beings arelungs, kidneys, skin and liver. These organs are discussed in greaterdetail in the sub-topics that follow this. Structure and function of mammalian skinThis is the largest body organ as it covers the whole body surfaceand even continues into many body openings like nostrils, mouthand ears. The main functions of the skin are: a Protection of the underlying tissues from entry of microorganisms, physical damage and ultra violet rays from the sun. B Regulation of body temperature. C Excretion of salts, excess water and traces of urea. D Reception of stimuli of heat, cold, pain, touch and pressure. E Synthesis of vitamin D. f Storage of fat. The skin is composed of two main layers. These are the upper layercalled the epidermis and the inner layer called the dermis. Seefigure 4.2. The epidermis is made up of three other layers that arediscussed later. Fig. 4.2: Structure of mammalian skin1. The malpighian layer: It is the innermost of the epidermallayers and is made up of actively dividing cells that give rise to anew epidermis. The cells have pigment granules called melaninthat gives colour to skin and also give protection against harmfulultraviolet rays from the sun.2. Granular layer is the middle layer of epidermis and consists ofliving cells that have granules. It gives rise to the cornified layer.3. Cornified layer is the outermost layer. It is made up offlattened dead cells that become filled with a tough flexiblesubstance called keratin. This layer is very important because itprovides protection against mechanical damage and invasion ofbacteria. It also reduces loss of water AUTHOR are continuously lost through friction and replacedfrom beneath AUTHOR.


This layer is very important because itprovides protection against mechanical damage and invasion ofbacteria. It also reduces loss of water AUTHOR are continuously lost through friction and replacedfrom beneath AUTHOR varies in the body,for example, it is thickest in areas of high friction like palms ofhands and soles of feet but thinnest on lips and eyeballs. The dermis is comparatively thicker than the epidermis. Manystructures such as blood vessels, nerve endings, lymphaticvessels, sweat glands and hair follicle are found in the dermis.4. Blood vessels and lymphatic vessels: Blood vessels containblood that supplies nutrients and oxygen to skin tissues andremove waste products and carbon IV oxide. Blood also helpsin temperature regulation. Lymphatic vessels drain excess tissuefluid.5. Nerve endings: The nerve cells which detect changes from theexternal environment thus creating awareness within the bodyof changes in temperature cold and heat , pressure and touch.6. Sweat glands are made up of a coiled tubule of secretory cellswhich extend into long tubules that opens on the surface of theskins as sweat pores. The secretory cells in the coiled tubuleabsorb excess water, mineral salts, traces of urea, lactic acid andcarbon IV oxide from the surrounding blood vessels andtissues. These substances are secreted into the tubule lumen toform sweat, which flow through the sweat duct to the skinsurface. Sweat glands are involved in body temperatureregulation through loss of excess heat AUTHOR 7. Hair originates from a deep infolding of the epidermis thatforms hair follicle. The hair follicle is lined with granular andmalpighian layers of epidermis. At the base of the hair is adermal or hair papilla from which hair root develops. The hairfollicle is supplied with sensory nerve to increase sensitivity ofthe skin and blood vessels for supply of nutrients and removal ofwaste products. Each hair is made up of a base called hair rootand hair shaft which protrudes outwards. Growth of the hair isdue to continuous addition of new dead cells at the base of thehair. Erector pili muscles are attached to the follicle at one endand on the other end to the epidermis.


Each hair is made up of a base called hair rootand hair shaft which protrudes outwards. Growth of the hair isdue to continuous addition of new dead cells at the base of thehair. Erector pili muscles are attached to the follicle at one endand on the other end to the epidermis. These muscles undergocontraction and relaxation to alter the angle between the hairshaft and skin and therefore vary the amount of air trappedbetween the hair and skin, a phenomenon that is important intemperature regulation.8. Sebaceous glands are attached to the follicle. The glandsopen into the follicle. They secrete sebum which keeps the hairand epidermis flexible and waterproof. Sebum containsantiseptic substances for protection against bacteria.9. Subcutaneous layer: This is a layer of fat beneath the dermisand binds the skin to muscles and other organs deep in thebody. It acts as a storage region for fats and an insulation layeragainst heat loss. NAME 2To observe the structure of the mammalian skinRequirementsPermanent slides of mammalian skin longitudinal section andmicroscopes. ProcedureObserve the slides provided under a microscope using low powerand medium power of the microscope. Study Questions1. Draw and label the structures observed.2. For the structures identified, state their functions. The LungsIn mammals, birds, reptiles and amphibians, carbon IV oxideformed during tissue respiration is removed from the body AUTHOR of animals, the lungs are made up of manysmall air sacs called alveoli. The alveoli have a thin, elastic, singlelayer of epithelium. Below this layer is a dense network ofcapillaries. Blood capillaries around the alveoli have a higherconcentration of carbon IV oxide than that in the alveoli space. This creates a concentration gradient that causes carbon IV oxideto diffuse out of the blood into the alveoli. The carbon IV oxide isthen expelled from the lungs through a process of exhalation. Forthe lung structure refer to chapter 2 of this book .Structure and Function of the KidneyThe kidneys are important organs in the body whose functions areexcretion, osmoregulation, ionic balance and regulation of pH. Amammal has a pair of kidneys located in the lumbar region of thedorsal part of the abdominal cavity.


The carbon IV oxide isthen expelled from the lungs through a process of exhalation. Forthe lung structure refer to chapter 2 of this book .Structure and Function of the KidneyThe kidneys are important organs in the body whose functions areexcretion, osmoregulation, ionic balance and regulation of pH. Amammal has a pair of kidneys located in the lumbar region of thedorsal part of the abdominal cavity. They are beanshaped and darkred in colour. The right kidney is more anterior than the left. NAME are the adrenal glands that secrete hormones. A kidneyis convex on one side and concave on the other side. The concaveside has a depression called hilum through which enters a renalartery to supply blood and renal vein to remove blood. From thehilum also leaves a large thick walled tube called ureter that linksthe kidney to an elastic thin-walled urinary bladder. The uretertransports urine from the kidney to the bladder, which temporarilystores the urine. When the urinary bladder is full, sphincter muscleslocated at the base of the bladder relax and urine is released viathe urethra. In males the urethra is long and is joined to thereproduction system unlike in females. See figure 4.3. Fig. 4.3: A generalised urinary system of a mammalA longitudinal section of mammalian kidney shows three distinctregions which include cortex, medulla and pelvis. The cortex whichis dark red in colour is placed to the inner convex surface. Themedulla which is red in colour, lies towards the centre of the kidneyand extends, in form of conical structures called pyramids. Thesepyramids open into swollen cavity called pelvis. The pelvis, which iswhitish in colour, narrows to form the ureter. The human kidneycontains urinary tubules known as nephrons. A human kidneycontains about five million nephrons. See figure 4.4 a and b . Fig. 4.4 a : Longitudinal cross-section of a mammalian kidneyFig. 4.4 b : Section through cortex and medullaPractical Activity 3To observe the structure of a mammalian kidneyRequirementsA mammalian kidney e.g. goats or any other available ones and ascalpelProcedure1. Observe the kidney provided.2. Draw and label the kidney showing external features.3.


This blood is rich in nitrogenous wastes e.g. urea. It alsocontains dissolved food substances, plasma, proteins, mineral ions,hormones and oxygen. The afferent arteriole entering the glomerulus is wider than theefferent arteriole leaving it. The narrowness of the efferent arterioleproduces both resistance to blood flow and back pressure whichcreate extremely high pressure in the glomerulus. Secondly therenal artery branches directly from the dorsal aorta whose bloodflow is at high pressure. These builds up high pressure within theglomerulus. Due to this pressure the liquid part of the blood anddissolved substances of low molecular sizes including urea, glucose,salts and amino acids are forced out of the glomerulus into thecavity of the Bowman s capsule. Large sized molecules in theplasma such as proteins and blood cells are not filtered out becausethe walls of capillaries of glomerulus and Bowman s capsule havevery small pores. Hence the blood which remains is rich in plasmaproteins and has little water. This process is known asultrafiltration and the filtrate formed is called glomerularfiltrate. The filtrate then flows from the capsular space into theproximal convoluted tubule of the nephron. As the filtrate flowsalong the renal tubules, most of the filtered substances in theglomerular filtrate, useful to the body are selectively reabsorbedback into the blood. In the proximal convoluted tubule, all theglucose, amino acids, some water and mineral salts are activelyreabsorbed against a concentration gradient a process thatrequires energy. For efficient reabsorption the proximal convolutedtubule is adapted in the following ways:Fig. 4.6: The structure of the kidney nephron i Cells lining the tubule have numerous mitochondria whichprovide the necessary energy in form of ATP. Ii Cells of the tubule have microcilli which increases the surfacearea. Iii The tubule is long and highly coiled to provide a large surface. Iv The coiling of the tubule reduces the speed of the flow of thefiltrate thereby giving more time for efficient reabsorption. V The tubule is well supplied with blood capillaries. The loop of Henle forms an area where salts especially sodiumchloride are reabsorbed into the blood.


For efficient reabsorption the proximal convolutedtubule is adapted in the following ways:Fig. 4.6: The structure of the kidney nephron i Cells lining the tubule have numerous mitochondria whichprovide the necessary energy in form of ATP. Ii Cells of the tubule have microcilli which increases the surfacearea. Iii The tubule is long and highly coiled to provide a large surface. Iv The coiling of the tubule reduces the speed of the flow of thefiltrate thereby giving more time for efficient reabsorption. V The tubule is well supplied with blood capillaries. The loop of Henle forms an area where salts especially sodiumchloride are reabsorbed into the blood. The U-shaped loop isgenerally longer and has a counter current flow establishedbetween the flow of filtrate and the large supply of blood in vessels. Active transport is involved in the reabsorption of sodium salts. Toregulate the intake of sodium salt, a hormone called aldosteroneis secreted AUTHOR of salt in bloodstimulates adrenal glands to secrete more aldosterone hormoneand therefore more salt is reabsorbed from the filtrate and viceversa. When the filtrate reaches the distal convoluted tubule, acontrolled amount of water is reabsorbed into the blood AUTHOR in two ways, first being due to the activeintake of sodium salt into the blood at the loop of Henle whichincreases the osmotic pressure of the blood. The second factorinvolves a hormone known as antidiuretic hormone ADH . Thishormone is secreted AUTHOR hormoneincreases the permeability of the tubule and blood capillaries towater. When there is excess water in the body for example, as aresult of excessive intake of fluids, the osmotic pressure of theblood falls causing the pituitary gland to reduce its secretion of ADHinto the blood. Water reabsorption in the tubule is thereby reducedand results in the production of large amounts of dilute urine. If, forexample, the body has lost excessive water through sweating,thereby raising the blood pressure, the pituitary gland will releasemore ADH which results in increased water reabsorption from thetubule into the blood.


When there is excess water in the body for example, as aresult of excessive intake of fluids, the osmotic pressure of theblood falls causing the pituitary gland to reduce its secretion of ADHinto the blood. Water reabsorption in the tubule is thereby reducedand results in the production of large amounts of dilute urine. If, forexample, the body has lost excessive water through sweating,thereby raising the blood pressure, the pituitary gland will releasemore ADH which results in increased water reabsorption from thetubule into the blood. This results in the production of little amountsof concentrated urine. It should also be noted that the distal convoluted tubule hassome modifications similar to those found in the proximalconvoluted tubule, that is, a large surface area, being surroundedby many blood capillaries and having a wall one cell thick. The filtrate in the collecting tubule becomes urine and tricklesdown into the collecting duct where it joins urine from the collectingtubules of other nephrons. The urine then flows into the pelvis viathe pyramid and is finally emptied into the urinary bladder throughthe ureter. About 1 to 2 litres of urine trickles into the urinarybladder in a day. In the urinary bladder, about 250 millilitres of urinewill initiate the urge to urinate. The sphincter muscles relax and theurine is passed out. The resultant urine composition of a healthyperson may be as follows:Water 95 Urea 2 Uric acid0.030 Creatinine 0.1 Salts of Na , K , Cl PO4 3 1.4 Ammonia 0.04 Proteins 0.0 Glucose 0.0 The quantity and concentration of urine in animals is affected byterrestrial, aquatic, desert conditions, the physiological and thestructural adaptations of the animals. For instance, in a desert rat,water reabsorption is maximised AUTHOR long loopof Henle. Study Questions1. Explain why glucose and proteins are absent in urine.2. Describe how to test for the presence of glucose and proteins inurine.3.


It is fatal if not treated. Kidney FailureIn situations where a kidney fails to function, the person can stilllead a normal life using the other kidney. However, if both kidneysmalfunction the individual will still survive if treated promptly. Suchtreatment can be administered in two forms. These are: a Kidney dialysis. B Kidney transplant. NAME and its StructureThe liver is the second largest organ after the skin and is a specialorgan of excretion because many excretory products are producedby it. It lies immediately beneath the diaphragm and is made up ofseveral lobes. It receives more blood per unit time than any otherpart of the body other than the heart. It receives blood from twoblood vessels, namely the hepatic portal vein and the hepaticartery. Blood flows out of the liver through the hepatic vein. The liver consists of a large number of lobules. Each lobule ismade up of many liver cells. The cells are arranged radially arounda central blood vessel which is a branch of the hepatic vein. Theblood supply to each lobule is from two sources, the hepaticartery and the hepatic portal vein. These vessels branchbetween the liver lobules. Between the plates of liver cells are channels called canaliculiwhich receive bile. The bile moves outwards to the periphery of thelobules where it collects into bile duct. See figure 4.7 a and b . Fig. 4.7 a : Structure of the LiverFig. 4.7 b : The liver lobulesThe Functions of the NAME liver performs many functions that contribute a lot tohomeostasis. There are:DeaminationAmino acids one absorbed from the gut, they are used in synthesisof proteins of the body. Excess amino acids or proteins cannot bestored in the body since the body does not have a mechanism forsuch storage. Excess amino acids not used, are broken down in aprocess of deamination. In this process the amino group NH2 ofthe amino acid is removed and used to form ammonia. Theammonia is taken into the ornithine cycle which is a series ofreactions resulting to the formation of urea, a less toxic substancethan ammonia.


Excess amino acids not used, are broken down in aprocess of deamination. In this process the amino group NH2 ofthe amino acid is removed and used to form ammonia. Theammonia is taken into the ornithine cycle which is a series ofreactions resulting to the formation of urea, a less toxic substancethan ammonia. The process is summarised as shown in theequation at the bottom of the page: The urea formed is releasedinto the blood stream and is eventually passed out in the urinethrough the kidney. DetoxificationSome of the metabolic activities of the liver result into theproduction of toxic substances which if left to accumulate, woulddestroy or harm the tissues of the body. The liver also receivesharmful substances AUTHOR , food or drinks. It thereforemakes these substances harmless and eliminate the substances inharmless forms in a process called detoxification. The liver cellsthrough oxidation, reduction, and combination with othersubstances carry out this process of detoxification. For example,hydrogen peroxide produced AUTHOR brokendown AUTHOR water and oxygen which areharmless. This enzyme is found in the liver. You will investigate thisaspect in NAME 4 .ThermoregulationThe liver carries out many metabolic reactions some beingendothermic while others are exothermic. Under conditions of lowtemperature the hypothalamus sends impulses to liver to increaseexothermic reactions producing more heat that is distributedthroughout the body AUTHOR worn out red blood cells is also broken down inthe liver and the residual pigments urochrome which give urine ayellow tinge is eliminated AUTHOR , bilirubin excreted via bilejuice into alimentary canal. Regulation of Plasma ProteinsPlasma protein are important components of the body. Majority ofthem are synthesised from amino acids in the liver. These includealbumin, fibrinogen, prothrombin and antibodies. Many of these areinvolved in regulatory mechanism of homeostasis. Digesting anddeaminating excess proteins also regulate their quantities. Erythrocytes have a life span of about 120 days after which they aretaken to the liver where they are broken down. Haemoglobin isbroken into a haem group and globin.


Many of these areinvolved in regulatory mechanism of homeostasis. Digesting anddeaminating excess proteins also regulate their quantities. Erythrocytes have a life span of about 120 days after which they aretaken to the liver where they are broken down. Haemoglobin isbroken into a haem group and globin. Globin is digested into aminoacids and enters the amino acid pool while the haem group ischanged in biliverdin and bilirubin and taken to gall bladder. Theseare later released into the gut as bile and then passed out throughfaeces. These two substances give faeces its characteristic browncolour. Other functions of the liver include the manufacture of redblood cells during the foetus stage, formation and elimination ofexcess cholesterol which is an important component cell membrane,regulation of fat metabolism, storage of blood, storage of vitaminsB, C, E, K and minerals. The other major function of the liver is blood sugar regulation. This will be discussed under homeostasis. NAME 4To investigate the effect of enzyme catalase on hydrogenperoxideCatalase is an enzyme present in living tissues of plants andanimals. Its role in living tissues is to break down hydrogenperoxide H2O2 produced during cellular respiration. Hydrogenperoxide is a highly toxic chemical substance which should not beallowed to accumulate in the tissues. RequirementsFresh piece of liver, 20 hydrogen peroxide, boiling tube, woodensplint, source of heat, scalpel and measuring cylinder. Procedure1. Measure 2 cm3 of the 20 hydrogen peroxide and put this inthe boiling tube.2. Cut a small piece of liver and put it into the boiling tube.3. Immediately test for the gas being produced using a glowingsplint.4. Record your observations.5. Write an equation for the reaction that occurs.6. What do you conclude from the experiment? NAME and DisordersLiver CirrhosisThis is the contraction and hardening of the liver due to death ofliver cells. A fibrous tissue replaces the dead cells. The disease iscaused AUTHOR such as alcohol, attack byeither bacteria or virus and liver parasites. Symptoms are slow in development and are normally seenwhen the disease is at advanced stages.


What do you conclude from the experiment? NAME and DisordersLiver CirrhosisThis is the contraction and hardening of the liver due to death ofliver cells. A fibrous tissue replaces the dead cells. The disease iscaused AUTHOR such as alcohol, attack byeither bacteria or virus and liver parasites. Symptoms are slow in development and are normally seenwhen the disease is at advanced stages. These symptoms includebody weakness, loss of weight, indigestion, poor appetite, pain inthe upper right quarter of the abdomen and occasional vomiting ofbloody material. If a large portion of liver is damaged, death mayresult. Control and Treatment a Avoid excess alcohol intake. B Avoid fatty diet. C Take adequate diet and varied easily digestible food. D Have bed rest most of the time. E Low salt intake. F Consult a doctor. HepatitisThis is the inflammation of the liver. It is a viral disease and twotypes are known namely: Hepatitis A and B. Hepatitis A is morecommon among children and young adults. It is infectious and is passed from one person to anotherthrough contact of body fluids, contaminated food, milk and water. The symptoms appear between two to six weeks. These includeloss of appetite, nausea, fatigue, jaundice yellow of skin andabdominal pain. Hepatitis B is common in adults. It is transmittedthrough contaminated injections, instruments and other implementsthat pierce the skin and lead to exchange of fluids such as blood,semen and saliva. Symptoms appear between three to four months. Hepatitis B is more serious than A because it is difficult to cure andcause more deaths. ControlProper disposal of sewage, vaccination, bed rest, and prescribeddiet. JaundiceThis is characterised AUTHOR and skin. Itresults from failure of the liver to excrete all the bile pigments fromred blood cell haemoglobin breakdown. The bile pigmentaccumulates in blood and hence the yellowing of the skin. Thishappens due to blockage of bile duct or destruction of the liver as incirrhosis and hepatitis or mass destruction of red blood cells incirculation as in erythroblastosis foetalis. HomeostasisAn organism lives in an environment that keeps on changing inmany of its factors, for example temperature, availability of water,food and fresh air.


Itresults from failure of the liver to excrete all the bile pigments fromred blood cell haemoglobin breakdown. The bile pigmentaccumulates in blood and hence the yellowing of the skin. Thishappens due to blockage of bile duct or destruction of the liver as incirrhosis and hepatitis or mass destruction of red blood cells incirculation as in erythroblastosis foetalis. HomeostasisAn organism lives in an environment that keeps on changing inmany of its factors, for example temperature, availability of water,food and fresh air. Similarly, changes occur in the body of theorganism due to the different metabolic activities and the effectsbrought about AUTHOR the environment. Many ofthese changes disrupt biological reactions being carried out in theorganism and lead to adverse effects on the health of the organism. A process that adjusts these changes in the body of an organism tooptimum standards or levels and therefore brings about a steadystate is called homeostasis. To understand the mechanism of homeostasis, there is need todistinguish two aspects of the environment to the organism that is,internal and external environments. The external environment is the immediate surrounding of theorganism. It may be aquatic or terrestrial. The internal environmentis the immediate surrounding of the body cells. It is the tissue orinterstitial fluid which surrounds cells in the body. It is formed fromblood plasma in capillaries. There are also other factors in theintercellular fluid that tend to fluctuate. These include osmoticpressure, temperature, ionic concentration and pH. These factorsthat must be kept at steady state or equilibrium in order for thecells to function properly. Principles of HomeostasisVarious body systems such as circulatory, excretory, endocrine hormonal and nervous, work in a co-ordinated way to bring abouthomeostasis. In order to maintain a state of balance in the internalenvironment, these systems work on a feed back mechanism. There are two types of feedback mechanisms: a Negative feedbackWhen a factor in the body such as temperature or blood sugarlevel drops below or shoots above the normal, it is detected andcorrective action is taken. Such an action is either: i An increase in the level if it was dropping or ii A decrease in the level if it was increasing. The response bringing about such corrective measures is callednegative feedback. It restores the condition to normal. Fig.


In order to maintain a state of balance in the internalenvironment, these systems work on a feed back mechanism. There are two types of feedback mechanisms: a Negative feedbackWhen a factor in the body such as temperature or blood sugarlevel drops below or shoots above the normal, it is detected andcorrective action is taken. Such an action is either: i An increase in the level if it was dropping or ii A decrease in the level if it was increasing. The response bringing about such corrective measures is callednegative feedback. It restores the condition to normal. Fig. 4.8: A generalised scheme of a homeostatic control process b Positive feedbackIn positive feedback, a change below or above the normal is notcorrected. Instead, what is meant to be corrective action leadsto further undesirable change from the normal as illustrated inthe figure 4.8 above. Role of Hypothalamus in Thermo-regulationThe hypothalamus is a small region between the cerebrum andcerebellum part of the brain. It acts as a thermo-regulatory centre. It has numerous temperature receptor cells which detect theslightest changes in body temperature. The external temperatureaffecting the body is determined AUTHOR relay the impulse to the hypothalamus throughthe sensory nerves. The internal temperatures are detected AUTHOR flows in the brain. The hypothalamus also controls other homeostatic processese.g. Osmoregulation and blood sugar regulation. Skin and Thermo-regulationThe mammalian skin plays a very important role inthermoregulation. The parts of the skin that are concerned withthermo-regulation are:Sweat GlandsSome animal possesses sweat glands on their skin. When the bodytemperature increases, the sweat glands increase the rate of sweatproduction. Water in the sweat evaporates AUTHOR latent heat of vaporisation from the body and a cooling effectresults. Hair and Erector pili MusclesWhen the body temperature lowers the erector pili muscles arestimulated to contract. This makes the hairs to stand erect on thebody surface, thus trapping more air. Air, being a bad conductor ofheat insulates the body against heat loss AUTHOR.