This meansthat a particular antibody combines with or responds only to aparticular antigen to make it harmless. Antibodies are produced by the lymphocytes. When harmfulorganisms or proteins invade the body, some lymphocytes startproducing antibodies which are complimentary to them. The bonemarrow and the thymus gland also begin to produce morepolymorphs phagocytes and lymphocytes respectively. Types of ImmunityNatural Immunity Innate Immunity Natural immunity is inherited and controlled. This trait can betransmitted from parent to offsprings. Acquired Immunity or Artificial ImmunityAcquired immunity can either be naturally or artificially induced. When attacked by diseases like small pox, chicken pox, measles,poliomyelitis, and mumps the people who recover completely fromthese diseases develop resistance to any subsequent infectionsfrom the same diseases. If these people become infected again by the same disease causingorganisms pathogens , they do not become seriously ill. This isknown as acquired immunity. In some instances people who havebeen exposed to milder forms of a disease develop a resistance tothe acute forms of the disease, e.g. those who have been exposedto the tuberculosis bacteria may not be affected by the moreharmful forms of the same disease although they had neversuffered from the acute disease before. On the other hand, a personwho has never been exposed to the tuberculosis bacteria is likely toget seriously ill with the disease. Artificial acquired immunity occurs when a mild form of adisease-causing organism is injected into the body of a healthyperson. The infection stimulates the production of the correspondingantibody which then destroys the pathogens. The body thereafterretains the memory of the structure of this antigen in itslymphocytes. When the body is attacked by the same disease, itproduces the specific antibodies which destroy the disease causingorganisms. This type of immunity is called artificial acquiredimmunity. What happens is that, on coming into contact withspecific antigens a group of B lymphocytes called committed cells in the lymph nodes undergo cell division to produce a group oflarge plasma cells. The plasma cells synthesise the antibodies whichare released into the lymph and eventually reach the blood. In theblood the antibodies destroy the invading organisms. A smallnumber of plasma cells remain in the lymph nodes for years, evenafter the antibodies have eliminated the original infection and areremoved from the blood.


The plasma cells synthesise the antibodies whichare released into the lymph and eventually reach the blood. In theblood the antibodies destroy the invading organisms. A smallnumber of plasma cells remain in the lymph nodes for years, evenafter the antibodies have eliminated the original infection and areremoved from the blood. This system provides a very rapidresponse to any subsequent infection by similar antigens. These methods of artificially inducing immunity has now beenadopted in many countries and many lives are saved from variousdiseases like smallpox, measles, poliomyelitis and tuberculosis. Thefirst work on immunisation was by a British doctor called EdwardJenner in 1797 who used a vaccine to prevent a smallpox attack. Hehad observed that most milkmaids did not suffer from smallpoxafter they had suffered from cowpox. He carried out an experimentby first making some scratches on a healthy boy and introducingsome pus from a pox vesicle of a woman suffering from cowpox. Later he introduced some pus taken from a woman suffering fromsmallpox into the boy s body. Doctor Jenner observed that the boy did not contract smallpox,though he only developed mild symptoms of the disease. Thus theboy had been immunised against the deadly disease because a mildantigen cowpox virus produced antibodies against the smallpox. Currently, the method of producing vaccines involves thetreatment of the disease causing organisms so that they areweakened. This treatment of pathogens is called attenuation. Theattenuated bacteria or viruses are then introduced into the body ofa healthy person or animal by either vaccination or inoculation. Theattenuated bacteria or viruses stimulate the production of specificantibodies by the body such that next time the body gets infectedby the pathogens, there will be no serious illness caused. Vaccinesgenerally contain attenuated disease causing organisms. Thesevaccines are currently produced commercially. The reaction of thebody to cowpox vaccine is an example of active immunisation. Similarly, the body actively makes its own antibodies against someantigens e.g. measles, whooping cough and poliomyelitis. In somecases the artificially acquired immunity is permanent andimmunisation is done only once in a lifetime. In some cases a booster vaccination is required to maintain immunity e.g. againstcholera, since the immunity lasts for a short time.

Secondary Biology Form 2 PB - Unknown.pdf


In somecases the artificially acquired immunity is permanent andimmunisation is done only once in a lifetime. In some cases a booster vaccination is required to maintain immunity e.g. againstcholera, since the immunity lasts for a short time. Artificial passive acquired immunity is achieved whenantibodies from another source e.g. serum, are directly introducedinto the body of a person. The serum containing the antibodies iscalled antiserum, and it may be effective for only a few weeks. This type of immunity is called passive because the body is notactivated to produce its own antibodies. In newly born babiesantibodies pass from milk produced by the mother, so providing thebabies with passive immunity to some diseases for a period of time. Study Questions25. Explain how immunity is achieved in human beings.26. Name two types of immunity you know.27. List three diseases that are effectively controlled throughvaccination. The Role of VaccinationVaccination protects individuals from infections of many diseasessuch as smallpox, tuberculosis and poliomyelitis and it prevents thespread of the diseases. Diseases like smallpox, tuberculosis andtetanus used to be killer diseases but now, due to the developmentof vaccines, individuals can be protected from them. It is nowbelieved that smallpox has been eliminated from the world since1977. Pregnant mothers should be immunised against tetanus atleast once before giving birth. Table 1.7: Immunisation for childrenPlate 1.5: Vaccination against various diseases is done when need arise Courtesyof EA Standard In children, vaccination against certain diseases is done at differenttimes. Immediately after birth, the baby should be immunisedagainst tuberculosis and polio. The baby should then receive acompound vaccine against whooping cough and tetanus. Thecompound vaccination should be repeated after 10-14 weeks. At theage of nine months, the child should be vaccinated against measles. Measles is a major child-killer disease. Vaccinations should be given at regular intervals see table1.7 . For example, booster injections of vaccines against polio inbabies have to be given regularly after every four weeks, for thefirst 16 weeks. It is also recommended that healthy children shouldbe exposed to chickenpox when young for the attack is severe whenthe children mature. Immunisation against other diseases should be done as advisedby the health officers.


Vaccinations should be given at regular intervals see table1.7 . For example, booster injections of vaccines against polio inbabies have to be given regularly after every four weeks, for thefirst 16 weeks. It is also recommended that healthy children shouldbe exposed to chickenpox when young for the attack is severe whenthe children mature. Immunisation against other diseases should be done as advisedby the health officers. Usually, people of all ages are vaccinated ifthere is an outbreak of diseases like cholera, see plate 1.5.Apart from immunisation the control of diseases can also bedone by restricting movement of people into and out of infectedareas. This method is called quarantine. It can be done atinternational, national or local levels. Facilities like water wells, should not be shared as long as thequarantine is in force. Internationally, before one enters anothercountry, one must be vaccinated against various diseases, andcertificates of vaccination obtained. In schools and homes, peoplesuffering from infectious diseases should be isolated to avoidinfection of healthy people. This minimises the spread of disease. Allergic reactionsAn allergy is a hypersensitive reaction to an antigen by the body. This occurs when the combination of an antibody with an antigenproduces a violent reaction or severe damage to the body. Allergicpeople are hypersensitive to materials like dust, pollen grains, somefoods, some drugs and certain air pollutants. The allergy manifests itself in various ways. In some people, oneating certain foods, rashes appear on the skin. Some drugs e.g.penicillin, chloroquine and aspirin can also cause rashes on the skin. Other allergic reactions are itching, sneezing, vomiting or difficultiesin breathing. The allergic conditions are brought about when the body reactsby overproducing antibodies against harmless antigens. Theantibody-antigen reaction takes place on the surface of cells thatburst open, releasing a chemical substance called histamine,Histamine increases the permeability of the epithelial cells thusmaking them take in fluid and swell up. The intercellular spaces toobecome filled with fluid, and swell. Histamine also causesinflammation and pain. A severe condition called anaphylaxissometimes occurs, in which blood vessels get dilated and thislowers the blood pressure to the extent of causing death. This ishow bee stings can cause death.


Histamine also causesinflammation and pain. A severe condition called anaphylaxissometimes occurs, in which blood vessels get dilated and thislowers the blood pressure to the extent of causing death. This ishow bee stings can cause death. Avoiding the allergens allergycausing substances or administration of the antihistamine drugscan control this. Organ TransplantsCurrently, a lot research is being done on organ and tissueregeneration and human immune system. Surgeons can replacedamaged tissues of organs using similar organs from other personsor animals e.g. the pig, in transplant operations. It has also beenpossible to transplant kidneys, liver, spleen, reproduction organs,parts of skin and limbs. Parts of organs or tissues transplanted on tolarger parts of recipient are called grafts. It is known that although two organisms belong to the samespecies, their immune systems may be so different that grafts maybe rejected by the recipient. In most cases grafts involving identicaltwins or those from same individual are not rejected. The grafts may be rejected because the body of the hostrecognises the new tissue or organ as foreign to it. The donor tissuehas antigens to which the host s leucocytes produce antibodies andthe tissue may be rejected; if not, the graft will take or beaccepted. Some transplants of hearts, kidneys, cornea of the eye,lungs and bone marrow have been carried out by using drugs thatsuppress the immune response of the host. A substance calledinterferon is also used to suppress rejection of grafts. In organtransplants, sophisticated machines are used to keep the organs tobe transplanted and the patient alive. Other suggested activities1. Stem ringing experiment on translocation. 2. Visit to a health clinic to collect data information on: i Allergies ii Blood groups iii High blood pressure iv HIV AIDS in the school locality. Revision Questions1. Figure 1.27 is a longitudinal section of the root apex. I Label the parts A to E. ii State the function of parts labelled C, D and E. iii Label zones 1-2. Iv What are the differences between zone 2 and 3?Figure 1.272. Figure 1.28 is a plan diagram from a cross-section ofdicotyledonous plant stem.


What were theblood groups of the two samples?15. People can die when they inhale gases from burning charcoal inpoorly ventilated rooms. Explain how this death comes about.16. A State two proteins in the blood which are responsible fordetermining the blood group of a person. B Give two reasons why a transport system is necessary inhigher animals.17. State any two adaptations of red cells to their functions. 18. What do you understand by the term double circulation?19. A Explain the differences between: i blood plasma and serum. Ii blood and lymph. Iii tissue fluid and blood plasma. B State the functions of the plasma.20. A Draw a large labelled diagram of internal structure of amammalian heart. B Describe the circulation in the heart. C Describe the working of the heart.21. A Describe two diseases and two disorders of blood vessels. Identify the causes of the disorders in a above and listtheir symptoms and treatment. B In a certain person, blood took a long time to clot after acut. What vitamin deficiency was the person likely to havebeen suffering from?22. A What do you understand by the term immunity? B State and discuss the two types of immunity. C What is a vaccination? State the role of vaccination inproviding immunity. D What causes allergies? CHAPTER TWOGaseous Exchange2.1 IntroductionThe process by which the respiratory gases oxygen and carbon IV oxide are passed across the respiratory surface is known asgaseous exchange. This is brought about by a concentrationgradient that exists between the body of living organisms and thesurrounding medium. In simple organisms, oxygen is absorbed bythe exposed surface of the body by simple diffusion. In morecomplex organisms, there are special organs such as lungs or gillswhich absorb oxygen and remove carbon IV oxide from the body. The importance of gaseous exchange in the living organisms isto promote oxygen intake for respiration and facilitate carbon IV oxide removal from the body as a wasted product of metabolism.2.2 Gaseous Exchange in PlantsGaseous exchange in plants involves two main respiratory gases:carbon IV oxide and oxygen. During daytime green plants take incarbon IV oxide and oxygen. The carbon IV oxide taken in isused for photosynthesis and oxygen produced as a by-product ofphotosynthesis is released into the atmosphere.


In morecomplex organisms, there are special organs such as lungs or gillswhich absorb oxygen and remove carbon IV oxide from the body. The importance of gaseous exchange in the living organisms isto promote oxygen intake for respiration and facilitate carbon IV oxide removal from the body as a wasted product of metabolism.2.2 Gaseous Exchange in PlantsGaseous exchange in plants involves two main respiratory gases:carbon IV oxide and oxygen. During daytime green plants take incarbon IV oxide and oxygen. The carbon IV oxide taken in isused for photosynthesis and oxygen produced as a by-product ofphotosynthesis is released into the atmosphere. However some ofthe oxygen produced is used in the same plant for respiration. Butsince the rate of photosynthesis proceeds faster than respiration atdaytime, excess oxygen produced is removed. However, respirationcannot provide enough carbon IV oxide for photosynthesis atdaytime hence more carbon IV oxide diffuses into the leaves. Atnight respiration proceeds in absence of photosynthesis in greenplants, hence plants take in oxygen for respiration but give outcarbon IV oxide. Plants do vary in their size and thus influence thesurface area to volume ratio for gaseous exchange. Whether insimple or complex plants, gaseous exchange takes place bydiffusion across the respiratory surface. In plants such as the flowering plants, stomata in the leavesand lenticels in the woody stems and roots provide surfaces forgaseous exchange. Practical Activity 1 a To investigate the release of carbon IV oxide by plantsRequirementsFreshly plucked leaves from a plant one boiled and another keptfresh , boiling tubes 2 , bicarbonate indicator solution red incolour and aluminium foil. Procedure1. Obtain a freshly plucked leaf of a plant.2. Put a litre of diluted bicarbonate indicator in the boiling tubethat has been covered with aluminium foil and label A.3. Using a piece of thread, suspend the leaf above the indicator inthe boiling tube.4. Place a cork to cover the mouth of the boiling tube as shown infigure 2.1.5. Set up a control with a boiled leaf and label B.6. Keep the apparatus on the side bench for at least one hour. Note: Bicarbonate indicator is red at the beginning of theexperiment. Study Questions1.


Place a cork to cover the mouth of the boiling tube as shown infigure 2.1.5. Set up a control with a boiled leaf and label B.6. Keep the apparatus on the side bench for at least one hour. Note: Bicarbonate indicator is red at the beginning of theexperiment. Study Questions1. Note the colour change of the bicarbonate indicator in practicalactivity 1 a above.2. Explain the colour change. Fig. 2.1: Release of carbon IV oxide by plants3. Why are boiling tubes covered with aluminium foil?Practical Activity 1 b To investigate the release of oxygen by plantsRequirementsWater plants, glass funnel, beaker, boiling tube, wooden block,wooden splints, sodium hydrogen carbonate and source of heat. Procedure1. Set up the experiment as shown in figure 2.2.2. Place the set-up in the sunlight to allow photosynthesis to takeplace. Fig. 2.2: Release of oxygen by plants3. Leave the set-up in the sunlight until sufficient gas has collectedin the boiling tube.4. Test the gas collected using a glowing splint. Study Questions4. What happens when the gas collected is brought near a glowingsplint?5. Identify the gas produced above and explain how plantsproduce it. Structure and function of the stomataStomata are tiny openings on the leaf surface bordered by sausageshaped guard cells. The guard cells are the only green cells of theepidermis. The inner sides of the guard cell are not attached to thewalls of the adjacent epidermal cells. Stomata occur mainly on thelower side of the leaf but less frequently on the upper side of theleaf surface that receive direct sunlight. Stomata open mostly atdaytime but close at night. However, their distribution on the leafsurface is related to the habitat. The stomata allow gaseousexchange to take place in the plants. Guard cells also control theopening and closing of the stomata. The guard cells are adapted totheir function by having differentially thicker inner cell walls. Seefigure 2.3 a and b .Fig. 2.3: a Stoma closedThe Mechanisms of Opening and Closing ofStomataThis process of opening and closing of stomata has been explainedby various theories.


The guard cells are adapted totheir function by having differentially thicker inner cell walls. Seefigure 2.3 a and b .Fig. 2.3: a Stoma closedThe Mechanisms of Opening and Closing ofStomataThis process of opening and closing of stomata has been explainedby various theories. One such theory is the photosynthetic theorybased on the sugar formation by chloroplast in the guard cells tobring about cell turgor. During the daytime the chloroplast of guardcells produces sugar through the process of photosynthesis. Thissugar accumulates in the guard cells causing the osmotic pressureof the sap vacuoles of the cells to increase. This leads to drawing ofwater from the neighbouring cells by osmosis. The guard cells thusbecome turgid and bulge outwards making the stomata to open. Atnight, however, sugar is converted to starch which accumulates inthe guard cells. The osmotic pressure of the guard cells then falls asthe cells lose turgidity due to water loss to the adjacent epidermalcells. This condition results in the guard cells becoming flaccid anddraw towards one another leading to the closure of the stomata. The above theory has been found unsatisfactory, as there are someplants whose stomata open at night and close at daytime. Another possible explanation of stomatal closing and opening isin the conversion of sugar to starch and vice versa in the guardcells. The starch sugar interconversion theory is under the influenceof pH through enzyme action. For example, during the dayphotosynthesis takes place in guard cells using carbon IV oxide. The pH in the guard cells tends to rise as the conditions becomeless acidic as carbon IV oxide is continuously used up. Theincreasing pH favours the conversion of starch into glucose. Theglucose being osmotically active, brings about an osmotic effectthat result in water being drawn into the guard cells. Consequently,the guard cells become turgid and bulge outwards making thestomata to open. At night carbon IV oxide is hardly used up asphotosynthesis does not take place. Carbon IV oxide, thereforeaccumulates in the guard cells resulting in the lowering of pH. Thisfavours the conservation of glucose into starch. Fig. 2.3 b Stoma openThe latter is osmotically inactive and therefore the guard cells donot gain water.


Carbon IV oxide, thereforeaccumulates in the guard cells resulting in the lowering of pH. Thisfavours the conservation of glucose into starch. Fig. 2.3 b Stoma openThe latter is osmotically inactive and therefore the guard cells donot gain water. Due to the resulting flaccid state of the guard cells,the stomata close. The closure may not be complete and somegaseous exchange may still take place at night. Mechanism of Gaseous Exchange in PlantsThe process of gaseous exchange in aerial roots, stems and leavesof both aquatic and terrestrial plants is the same. For gaseousexchange to take place, a concentration gradient must existbetween the atmospheric air outside and that in the interior of theroot, stem or leaf. This will permit oxygen to diffuse from theatmospheric air outside where its concentration is high, into theplant where its concentration is kept low due to utilisation inrespiration. Similarly, carbon IV oxide will diffuse out as ametabolic waste product along a concentration gradient into theatmosphere. Fig.2.4: A transverse section of a water lily showing the large airspacescharacteristic to hydrophytesStomata and Habitats of PlantsStomata are also modified in a number of ways depending on thehabitat in which the plant is growing. For example, xerophytes plants adapted to living in dry areas often have fewer stomatathat are smaller in size than those of hydrophytes plants in wetareas . These stomata are found mainly on the lower surface of theleaves. In some xerophytes the stomata are sunken and in othersthey open during the night and tend to close during daytime. Thepartial opening during the daytime allows for gaseous exchange. The modifications mentioned above, help in water conservation inthe tissues of the plant and at the same time reduce water lossfrom the plants by evaporation and transpiration. Hydrophytes are aquatic plants or plants growing in water. Some of these aquatic plants, are not completely submerged, forexample nymphea. They have many stomata that are large in size. Their stomata are mainly found on the upper surface of leaves. These stomata allow the hydrophytes to release excess water tothe atmosphere.


Thepartial opening during the daytime allows for gaseous exchange. The modifications mentioned above, help in water conservation inthe tissues of the plant and at the same time reduce water lossfrom the plants by evaporation and transpiration. Hydrophytes are aquatic plants or plants growing in water. Some of these aquatic plants, are not completely submerged, forexample nymphea. They have many stomata that are large in size. Their stomata are mainly found on the upper surface of leaves. These stomata allow the hydrophytes to release excess water tothe atmosphere. The hydrophytes also have aerenchyma tissuewith large air spaces to store air for gaseous exchange as shown infigure 2.4.The mesophytes terrestrial plants growing in moist areas orareas with adequate water supply have a fairly large number ofstomata of medium size found on both surfaces of the leaves inmore or less equal numbers. Structure and Function of LenticelsLenticels are openings found on the stems and roots of some woodyplants and usually are formed by loosely packed corky cells. Theseopenings permit gaseous exchange to take place between theinterior of the plant and the outside by diffusion. The actualgaseous exchange takes place on the moist surfaces of cells underthe lenticels. However, in some aquatic plants such as themangrooves, plants that grow in muddy salty waters on beaches lenticels in specialised breathing aerial roots called pneumatophoresallow gaseous exchange to take place. See figure 2.5 and plate 2.1. Fig. 2.5: The structure of the lenticelPlate 2.1: Pneumatophores of the mangroovesPractical Activity 2To observe permanent slides of transverse sections ofleaves and stemsRequirementsPermanent slides of mesophyte, zerophyte and hydrophyte leaves,stems and light microscope. Procedure1. Place each slide in turn on the stage of the microscope andobserve.2. Draw a labelled plan diagram of each specimen observed. Study Question6.


2.5: The structure of the lenticelPlate 2.1: Pneumatophores of the mangroovesPractical Activity 2To observe permanent slides of transverse sections ofleaves and stemsRequirementsPermanent slides of mesophyte, zerophyte and hydrophyte leaves,stems and light microscope. Procedure1. Place each slide in turn on the stage of the microscope andobserve.2. Draw a labelled plan diagram of each specimen observed. Study Question6. How are the structures observed related to gaseous exchange,for the mesophyte, xerophyte and hydrophyte?2.3 Gaseous Exchange in AnimalsTypes and Characteristics of RespiratorySurfaces in AnimalsVarious types of respiratory surfaces have been developed bydifferent animals to facilitate gaseous exchange depending on theanimal s size, activity and the environment in which it operates. Table 2.1: Types of respiratory surfaces in animalsType of respiratorysurfaceEnvironment or mediumof operationExample oforganism i Cell membraneWaterAmoeba ii Gill filaentsWaterFish iii TracheolesAirInsects iv Alveoli lungsAir Mammals Birds Frogs Reptiles v Skin vi Buccal cavityWaterAirFrogEarthwormAirFrogThe respiratory surface is the basic unit of any breathing systemupon which gaseous exchange takes place by diffusion. However,the respiratory surface must meet the conditions listed below toallow gaseous exchange to take place effectively. These are: i It must have a large surface area. Ii It must always be a moist surface. Iii It should possess a rich capillary network. Iv It must be a thin membrane. The above-mentioned conditions constitute characteristics of mostrespiratory surfaces. Gaseous Exchange in ProtozoaThe example of the amoeba, a member of the kingdom protoctistais used to represent protozoa. 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 by diffusion across its cell membrane. Oxygen dissolved in the surrounding water, diffuses across themembrane into the cytoplasm.


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 by diffusion across its cell 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 into finer 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 Gaseous Exchange in theTracheal System of an InsectAir is drawn into and out of the tracheal system by muscularmovement of the abdominal 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 by the muscle movements. Oxygen 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 by valves when the larvasubmerges. 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 by valves when the larvasubmerges. 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 by hairs or other structures 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 by the head and using 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. Gaseous Exchange 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. Gaseous Exchange 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 by a larger bony plate 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 Gaseous Exchange in the Gillsof Bony FishThe floor of the mouth cavity is lowered by muscular contractionsduring inhalation. Lowering 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. By the time the blood 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 Gaseous Exchange inAmphibiansAmphibians by nature live on both land and in water. This doublehabitation calls for special adaptation in gaseous exchange. Theyachieve this by employing the listed methods 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 by theaction of the mouth. 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 by raising andlowering the floor 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 by haemoglobin to all parts ofthe body. Carbon IV oxide from the tissues is brought by the bloodto the mouth 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 by the pumpingaction of the 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 by the blood and diffuses into thealveoli, then pumped out by the pumping action of 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 Gaseous Exchange 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 by a fine network of bloodcapillaries as shown in figure 2.16 c on page 60.Practical Activity 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. The Mechanism of BreathingBreathing is accomplished by changes in volume and air pressure ofthe thoracic cavity. The thoracic cavity is enclosed by ribs which areattached to the vertebral column at the back and sternum in front. The ribs are covered by intercostal muscles, 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. The Mechanism of BreathingBreathing is accomplished by changes in volume and air pressure ofthe thoracic cavity. The thoracic cavity is enclosed by ribs which areattached to the vertebral column at the back and sternum in front. The ribs are covered by intercostal muscles, 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 by movement of the ribs 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 by the contraction of its 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 by the following: 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?Practical Activity 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 by a film of moisture 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 by a film of moisture 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 by the same process. Table2.2 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 by increasedrespiration.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 by increasedrespiration.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. Practical Activity 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 by sucking in from thetest-tubes 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 by bacteria or viruses.


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 by bacteria or viruses. Therespiratory 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 by muscular contractions. The patient,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 by ahealth physician. 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 by uncomfortable feelings behind thesternum. 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 by uncomfortable feelings behind thesternum. 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. Whooping CoughWhooping 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 by peri-orbitaloedema. 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 by micro-organisms. There are several types of pneumonia caused by different bacteria. Common ones include: i Lobar pneumonia caused by attacks of Streptococcuspneumoniae. Symptoms of 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 by a bacterium calledMycobacterium tuberculosis.


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 by a bacterium calledMycobacterium tuberculosis. 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 by radiographicalmethod. 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 By not smoking actively and passively and in foodpreservatives. Study Question18. Suggest how too much dust particles may affect therespiratory system. Revision Questions1. What is meant by the term gaseous exchange? 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 by fourgroups of students for 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 by the disease. Give a 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 by the disease. Give a 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 by a disease.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 by thefollowing: 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 Severe Acute 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 by which food substances are 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. Practical Activity 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 RespirationAll 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 RespirationThere 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 by yeasts and many bacteria.


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 by yeasts and many bacteria. 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 by oxygenin a series of 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. Practical Activity 2To investigate production of heat by germinating seedsRequirementsBoiled bean seeds, 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 by seeds. 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 by germinating seedsStudy Questions2. 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 by germinating seedsStudy Questions2. What does production of heat in the germinating beans imply?3. Explain by what process the heat in i above is produced. Anaerobic Respiration in Plants and AnimalsAnaerobic respiration is the process by which food substances suchas 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 by bacteria results in the production of energy and lactic acidwhich causes milk to become sour. Oxygen Debt 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 by the person breathing more 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 by the person breathing more 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 Anaerobic Respiration 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. In Kenya,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 by fermentationdepends largely on the 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. Practical Activity 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.Comparison Between Aerobic 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 by feeding on plants. Some 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 by feeding onother animals or 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 by feeding on plants rich inproteins or on other animals or animal products such as lean meat,milk, eggs and cheese. Respiratory Quotient 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 by the amount of oxygen 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 Respiration Quotient 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 Respiration Quotient 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 by which living organisms separate 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 by which living organisms separate 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 by excretion. On the other hand, secretion is the release ofcertain useful substances produced by cells. Such substancesinclude hormones, 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 by excretion. On the other hand, secretion is the release ofcertain useful substances produced by cells. Such substancesinclude hormones, 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 by the plant. These waste products include carbon IV oxide, oxygen and water. The gases are removed from the plant by rapid diffusion throughthe stomata 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. Economic Importance 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 by animal proteases. Extracts of 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. Practical Activity 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 by simple diffusion.