The following simpletissues may be found within it: parenchyma, collenchyma andsclerenchyma. NAME cortex collenchyma tissue lies just beneath the epidermis. Itmay form a complete cylinder or it may occur in separate strands. From a longitudinal view, collenchyma cells are elongated and havea pointed oblique ends. The walls are thickened at the corners withcellulose and pectin deposits. Due to this thickening, collenchymaserves as a strengthening tissue. ParenchymaParenchyma tissue constitutes the greater part of the cortex. Thecells are irregular in shape, thin walled and loosely packed, hencecreating intercellular spaces filled with air. The cells function in thestorage of water and food. Some cells contain chloroplasts andtherefore photosynthesise. These cells are known aschlorenchyma and make some stems green. SclerenchymaThe cortex sclerenchyma is found in close association with thevascular bundles. The walls of the sclerenchyma cells are thickenedby deposition of lignin in a process known as lignification. Likethe collenchyma, the sclerenchyma serves as a strengtheningtissue. The PithThe pith is the central region of the stem. It consists of parenchymacells that store water and food substances. In some stems, the pithmay be hollow. Vascular bundlesVascular bundles consist of highly specialised cells that arecontinuous from roots through the stem to the leaves. Theytransport water and dissolved minerals from the roots up the plantand the products of photosynthesis from the leaves to the rest ofthe plant body. NAME 3To observe the internal structure of stemsRequirementsLight microscope, slides of transverse sections of: i the monocotyledon stem ii the dicotyledon stem. Procedure1. Place the permanent slide of the monocotyledon stem on themicrocsope.2. Observe under the low power and medium power of themicroscope.3. Draw a labelled plan diagram of the section.4. Repeat the above procedure with the other slide of the dicot. Study Questions6. What tissues make up the vascular bundles?7.


Draw a labelled plan diagram of the section.4. Repeat the above procedure with the other slide of the dicot. Study Questions6. What tissues make up the vascular bundles?7. Draw plan diagrams to show the arrangement of vascularbundles in a named: i monocotyledon ii dicotyledon stem. Absorption of water and mineralsalts a Absorption of waterWater is drawn into the root hair cells AUTHOR of dissolved substances in the cell sap of root hairs, theconcentration of the cell sap is greater than that of the surroundingsolution in the soil. A concentration gradient therefore, existsbetween the sap in the vacuole of the root hair cell and the soilwater. This exerts a higher osmotic pressure, thus drawing thewater molecules across the cell wall and cell membrane into theroot hair cells. The osmotic forces exerted AUTHOR , overcomethe water retaining powers of the soil thereby enabling water in thesoil to enter the root. More water drawn into the root hair cellsdilutes the cell sap making it less concentrated than that in theadjacent cortex cell of the root. Due to osmotic gradient, watermoves from the adjacent cells to the next AUTHOR ,water passes through the successive cortex cells until it enters thexylem vessels located in the centre of the root. These xylem vesselsof the root then conduct the water up into the xylem vessels of thestem into the leaves as shown in figure 1.4 a , b and c . Fig. 1.4: Absorption of water AUTHOR b Uptake of Mineral SaltsThe soil water contains dissolved mineral salts which plants requirefor their growth and proper functioning. They must therefore beabsorbed from the soil into the plant. Generally, the concentrationof the cell sap in the root hairs is greater than that in the soil. Themineral salts therefore enter the root hairs against theconcentration gradient. This suggests that salts can be drawn fromthe soil even when their concentration is lower than that in the rootcells. This process requires the use of energy and is thereforereferred to as active transport. Any substance that hindersrespiration inhibits active transport. Active transport is believed to involve substances known ascarriers.


This suggests that salts can be drawn fromthe soil even when their concentration is lower than that in the rootcells. This process requires the use of energy and is thereforereferred to as active transport. Any substance that hindersrespiration inhibits active transport. Active transport is believed to involve substances known ascarriers. These carriers are believed to combine with the mineralions and then carry them across the plasma membrane into the cell. Thus the carriers move back and forth carrying the salt ions fromthe soil water to the root hair cells. Like water, the mineral salts after absorption move through theroot cells into the xylem vessels of the vascular tissue in the centreof the root. Once inside these vessels, the salts and water arecarried up the stem into the leaves AUTHOR which include osmosis, diffusion, root pressure,transpiration stream, cohesive forces and capillary attraction. TranspirationTranspiration is the process AUTHOR in the formof water vapour into the atmosphere. Water loss from the plantsoccurs from the following sites: stomata, cuticle and lenticels. I Stomatal TranspirationThis is the loss of water vapour through the stomata. It accounts for80-90 of the total transpiration in plants. Most of the stomata arefound on the leaves but may also occur on the epidermis of youngherbaceous stems. Ii Cuticular TranspirationThis is the loss of water in the form of water vapour through thecuticle. Up to 20 of the total transpiration may take place throughthin cuticles. In plants with thick cuticles, the loss is negligible. Iii NAME is the loss of water in the form of water vapour through thelenticels. These are areas with loosely fitted cells on woody stems. The loss through the stem is negligible. The internal structure of a leaf in figure 1.5 shows that eachstoma opens into the substomatal air spaces that are lined withspongy mesophyll cells. As water vaporises from the spongymesophyll cells into the sub-stomatal air spaces their cell sapbecomes concentrated than the adjacent cells. This increasesosmotic pressure of the spongy mesophyll cells. As a result, waterflows into the cell from other surrounding cells which in turn take inwater from xylem vessels within the leaf veins. Fig.


As water vaporises from the spongymesophyll cells into the sub-stomatal air spaces their cell sapbecomes concentrated than the adjacent cells. This increasesosmotic pressure of the spongy mesophyll cells. As a result, waterflows into the cell from other surrounding cells which in turn take inwater from xylem vessels within the leaf veins. Fig. 1.5: The internal structure of a leafYou therefore notice that the water lost through the leaf comesinto the leaf through the xylem in the leaf which is in continuousconnection with the xylem of the stem and that of the root. It istherefore necessary to study the structure and function of thexylem. Structure and function of xylem tissueXylem tissue is made up of two main types of cells namely vesselsand tracheids. In some plants both types of cells are present. Xylem VesselsThese are tubular and non-living tissues as shown in figure 1.6.During cell differentiation, the cross walls of the cells which formthe vessels and the cytoplasm disintegrate resulting into a longhollow tube running continuously from the roots through the stemto the leaves. The walls of the vessels are strengthened bydeposition of lignin material that prevents them from collapsing. The patterns of lignification are diverse as shown in figure 1.6. Thebordered pits on the xylem vessels permit the passage of water inand out of the lumen into the neighbouring cells. Xylem vessels arecharacteristic features in flowering plants angiosperms . Theefficient conduction of water and mineral salts through the floweringplant is the function of the xylem vessels. TracheidsLike the vessels, tracheids are modified xylem cells with lignifiedpitted walls and are non-living. Unlike the vessels, tracheids havetapering or chisel-shaped ends and the cross walls remainperforated. The pits on the sidewalls allow lateral water to cellssurrounding the xylem. See figure 1.7. Aaa ee Fig, 1.6: Xylem vessels - NAME 1.7: NAME makes them less efficient in conducting water than the vessels. Tracheids perform both functions of support and transportation ofwater in the pteridophytes, gymnosperms and angiosperms. Study Questions8.


The pits on the sidewalls allow lateral water to cellssurrounding the xylem. See figure 1.7. Aaa ee Fig, 1.6: Xylem vessels - NAME 1.7: NAME makes them less efficient in conducting water than the vessels. Tracheids perform both functions of support and transportation ofwater in the pteridophytes, gymnosperms and angiosperms. Study Questions8. I Why are the xylem vessels more efficient in transportationof water than tracheids? Ii What is the significance of xylem vessels being dead?Forces involved in Transportation of NAME saltsAs water evaporates from the plant, more is absorbed from the soil. This forms a continuous stream of water flowing from the roots, upthe stem to the evaporating surface. This continuous flow of wateris known as the transpiration stream. See figure 1.8. Thetranspiration stream carries water and salts in solution form, fromthe roots to the leaves. This flow takes place in the xylem tissues. The forces behind this continuous flow of water and mineral saltsthrough the plant include: transpiration pull, cohesion and adhesionforces, capillary and root pressure. These forces are discussed indetail below. I Transpiration pullAs water vaporises from the spongy mesophyll cells into the substomatal air spaces, their cell sap becomes concentrated than theadjacent cells. This change increases the osmotic pressure of thespongy mesophyll cells. As a result, water flows into the cell fromother surrounding cells which in turn take in water from xylemvessels within the leaf veins. These developments create a pull orsuction force that pulls a stream of water from the xylem vessels inthe stem and roots. It is this force that is referred to astranspiration pull, that partly maintains the continuous column ofwater from the roots to the leaves. This is important in thereplacement of water lost from the plant through transpiration. Fig. 1.8: Water loss and transpiration in plants ii Cohesion and Adhesion forcesWater molecules attract one another in such a way that they alwaysstick together. The forces that keep them together are referred toas cohesion force.


Fig. 1.8: Water loss and transpiration in plants ii Cohesion and Adhesion forcesWater molecules attract one another in such a way that they alwaysstick together. The forces that keep them together are referred toas cohesion force. At the same time water molecules areattracted to the walls of the container in which the water iscontained AUTHOR as adhesive force. The cohesive and adhesive forces in very thin columns can bevery high and not easily broken. These forces are important in themaintenance of a continuous and an uninterrupted water column inthe xylem vessels up the trees. Iii CapillarityIf an open ended tube is placed vertically with one end immersed inwater, the liquid will rise in the tube until the weight of the watercolumn balances the attractive forces operating between the waterand the walls of the tube. The narrower the tube the higher liquidwill rise. In a glass tube of 0.01 mm diameter, water will ascend AUTHOR of about three metres. In the xylem vessels,water would rise to some extent because the vessels are narrower,and there is a higher attractive force between the water moleculesand the cell walls. For effective capillarity there should be no airbubble in the water column. Iv Root PressureIf the stem of a plant is cut above the soil level, it is observed thatcell sap, continue to exude from the cut surface of the stump forsometime. This shows that, there is a force in the roots that pusheswater up the stem. This force is known as root pressure and canbe considerably high in some plants like the grape vines. Root pressure may be attributed to the active pumping of wateracross the endodermis to the xylem vessels. Energy is essential inthis process. Respiratory inhibitors such as cyanide, reduce rootpressure. Significance of TranspirationTranspiration makes the plant lose water if unchecked. However,transpiration has some beneficial effects on the plant as follows: i It serves to replace water lost through the leaves. Ii Through the process, mineral salts and water are transportedin the plant. Iii It serves to cool the plants, a significant factor especially inhot environments. Iv It helps in the removal of excess water especially in aquaticplants. V It is responsible for turgor in plants. Factors affecting Transpiration RateFactors that affect the rate of the transpiration can be grouped intostructural and environmental. These factors are discussedbelow.


Respiratory inhibitors such as cyanide, reduce rootpressure. Significance of TranspirationTranspiration makes the plant lose water if unchecked. However,transpiration has some beneficial effects on the plant as follows: i It serves to replace water lost through the leaves. Ii Through the process, mineral salts and water are transportedin the plant. Iii It serves to cool the plants, a significant factor especially inhot environments. Iv It helps in the removal of excess water especially in aquaticplants. V It is responsible for turgor in plants. Factors affecting Transpiration RateFactors that affect the rate of the transpiration can be grouped intostructural and environmental. These factors are discussedbelow. I Structural factorsThese are factors related to the morphology of the leaf.1. CuticlePlants growing in arid or semi-arid habitats have their leavescovered with a thick layer of cuticle. The cuticle is a waxywaterproof material. The cuticle reduces rate of transpiration. This may be seen inplants such as sisal, cactus, and aloe. Plants growing in wet habitatshave the problem of containing too much water in their tissues. Such plants have a very thin layer of cuticle on their leaves. Thethin cuticle allows high rate of transpiration as a means of gettingrid of excess water.2. NAME and ShapeThe rate of transpiration is high in plants with broad leaves. Thisexposes a large surface area for water loss as compared to theplants with small and sometimes needle-like leaves. Therefore,plants growing in habitats where water is scarce usually haveleaves with small surface area to minimise transpiration.3. StomataSince transpiration takes place mainly through the stomata inleaves, their position in the leaf, number and size of the apertureare very important as far as transpiration is concerned. Most landplants have few or no stomata on the upper leaf surfaces, but manyon the lower surface. In desert plants, the number of stomata onthe leaves is greatly reduced. Some have got their stomata sunkenbelow the epidermis forming pits. Water vapour tends toaccumulate in these pits thus reducing transpiration. Many plants close their stomata if the rate of transpiration ishigher than that of water uptake. Plants will close their stomata ona hot dry sunny day to lower the rate of transpiration. Thisphenomenon known as midday closure, protects the plant fromwilting.


Water vapour tends toaccumulate in these pits thus reducing transpiration. Many plants close their stomata if the rate of transpiration ishigher than that of water uptake. Plants will close their stomata ona hot dry sunny day to lower the rate of transpiration. Thisphenomenon known as midday closure, protects the plant fromwilting. Some desert plants have reversed stomatal rhythm,closing their stomata during the day and opening them at nightwhen the atmosphere is cool. Such a mechanism helps them toconserve water in their tissues.4. Leaf FallDuring periods of drought, some plants such as the broad-leafeddeciduous trees shed their leaves to reduce the surface area forwater loss. In some species of grass, the aerial shoot dries up toground level.5. Hairy LeavesIn some plants leaves are covered with hairs or scales. These trap alayer of still moist air on the surface of the leaves, thus reducingtranspiration. Ii Environmental FactorsThese factors are related to environmental conditions.1. TemperatureHigh temperature increases the capacity of the atmospheric air tohold more water vapour. High temperature increases the internaltemperature of the leaf which in turn increases latent heat ofvaporisation and therefore enhances evaporation from the leaf cells. The rate of transpiration increases. The reverse takes place whentemperature is low.2. HumidityThe rate of transpiration is generally high in dry atmosphere due tohigh concentration of water vapour in the intracellular air spacesthan in the dry atmosphere. This causes water vapour to diffuse outof the leaf into the dry atmosphere. The humidity differencebetween the inside and outside of the leaf is known as thesaturation deficit and it determines the rate of water loss fromthe leaf. In dry atmosphere, saturation deficit is high. Consequently,the rate of transpiration in dry atmosphere is high. On the otherhand, in high humidity the saturation deficit is low therefore therate of transpiration is low. Under such conditions some plantssecrete droplets of water through specialised pores calledhydathodes. This process of water loss is called guttation and iscommon in hydrophytes plants growing in wet habitats .3. WindStudy the sketch graph below showing the relationship betweenwind and the rate of transpiration. Wind carries away water vapouras fast as it diffuses out of the leaves through the stomata. Thisprevents the air around the leaves from being saturated with watervapour.


WindStudy the sketch graph below showing the relationship betweenwind and the rate of transpiration. Wind carries away water vapouras fast as it diffuses out of the leaves through the stomata. Thisprevents the air around the leaves from being saturated with watervapour. This helps to maintain a high diffusion gradient between theinside and outside of the leaf. On a windy day the rate transpirationis high. However, when the air is still the region around the leafsoon becomes saturated with water vapour. Diffusion of watervapour from the leaf surface is low leading to low transpiration rate. Fig. 1.9: Effects of wind on rate of transpiration4. NAME intensity affects transpiration rate AUTHOR of most plants open fully during daylighthours when light intensity is high. This brings the sub-stomatal airinto direct contact with the external environment. The water vapourtherefore diffuses out at a higher rate than in dim light whenstomata are partially closed. It is important to note that in a naturalsetting, these factors do not influence transpiration in isolation.5. Atmospheric PressureThe lower the atmospheric pressure the greater the rate ofevaporation. Plants found at high altitudes where atmosphericpressure is very low are likely to lose a lot of water due to high rateof transpiration. Most of them have adaptations to preventexcessive water loss.6. Availability of WaterTranspiration depends on walls of the mesophyl cells beingthoroughly wet. A plant must have adequate water supply from thesoil. NAME 4To investigate the rate of transpiration from leaf surfacesRequirementsLeafy shoots, anhydrous cobalt II chloride paper, glass slides,elastic bands, stop watch or stop clock, cellotape and a pair offorceps. Procedure1. Select one broad healthy leaf on a potted plant or herbaceousplant growing outside the laboratory.2. Using a pair of forceps pick two large pieces of anhydrous cobalt II chloride paper and quickly place each piece on the twosurfaces of the leaf. Note the colour of anhydrous cobalt II chloride paper. 3. Quickly cover them with the dry glass slides and note the time.4. Secure the slides into position with elastic rubber bands asshown in figure 1.105.


3. Quickly cover them with the dry glass slides and note the time.4. Secure the slides into position with elastic rubber bands asshown in figure 1.105. Separately note the time taken AUTHOR cobalt II chloride papers to turn pink. Note the time as soon a pink spotappears and also when the whole paper turns pink.6. Hold a covered piece of anhydrous cobalt II chloride paper toact as a control. This can be held in the hand with a pair offorceps.7. Note the time it takes the piece of paper to turn pink in the air. Do not handle anhydrous cobalt II chloride paper directly withyour hands.8. Record your results in form of a table showing time taken byanhydrous cobalt II chloride paper to turn pink while in the airor above water, under leaf surface and above leaf surface. Study Questions9. What conclusion can be made from this experiment regardingrates of transpiration on leaf surfaces?10. A Explain the difference that is noticed between theanhydrous cobalt II chloride paper on the lower leafsurface and that on the upper surface of the leaf. B i Why was a control experiment necessary? Ii Why is it not advisable to hold the anhydrous cobalt II chloride paper using bare fingers? Fig. 1.10: Experimental set-up for investigation of the rate of transpiration fromthe leaf surfacePractical Activity 5To investigate the rate of transpiration AUTHOR potometerRequirementsLeafy shoots of herbaceous plants, sharp knife or blades,potometers, beakers, plastic rulers, retort stands, rubber bands,water, jelly, large water container like a basin and stop watches orwristwatches. Procedure1. Obtain suitable leafy shoots from herbaceous plants and keepthe stem under water in a trough, basin or sink.2. Assemble a potometer as shown in figure 1.10. Select a suitableleafy shoot and cut off the last few centimetres of the stalkunder water in the sink. 3. Stand the base of the shoot in the water to prevent blockage ofthe water channels with air. Fix a rubber bung over the cut endwhile it is still in water.4. Connect the end of shoot in the bung to the potometer alreadyfilled with water.


Stand the base of the shoot in the water to prevent blockage ofthe water channels with air. Fix a rubber bung over the cut endwhile it is still in water.4. Connect the end of shoot in the bung to the potometer alreadyfilled with water. Apply jelly to the stem around the rubber bungto render the system airtight.5. Transfer the set-up to a bench near a window in the laboratory. The end of the capillary tubing should rest in a beaker of water. For a commercially made potometer that is already mounted,dipping of capillary in a beaker of water is not required. Open up the reservoir tap and run out the water to expel any air inthe capillary tube. When all the air has been expelled, introduceone air bubble into the capillary tube. This is done AUTHOR the beaker for a few seconds. Adjust its position using the reservoir tap. The bubble should bemoved to the end of the capillary tube. Place a plastic rubberbehind the capillary tube to measure rate of movement of the airbubble per unit time. Leave the set-up in this position and recordthe position of air bubble and time. When the bubble has travelledmost of the length of the ruler, note the position of the air bubbleand the time. From this, find the distance moved and time taken. Transfer the set-up to other areas such as next to a workingfan, bright light or shaded area. Tabulate the results and explainthem. Fig. 1.11 Set-up of a potometerTranslocation of Organic CompoundsThe transport of soluble organic products of photosynthesis withinthe plant is known as translocation. It occurs in the phloem of thevascular tissues. Like the xylem vessels, the phloem tubes run fromthe roots to the leaves. The organic products translocated aremainly food materials. These products of photosynthesis includesugar, amino acids and vitamins.


Like the xylem vessels, the phloem tubes run fromthe roots to the leaves. The organic products translocated aremainly food materials. These products of photosynthesis includesugar, amino acids and vitamins. They are translocated to differentregions of the plant where they are required for various purposes. These regions include: a The growing and developing regions of the plants such asyoung shoots, leaves, flowers, fruits and roots. B The storage organs or tissues such as tubers, corms, bulbs,rhizomes and seeds. C The secretory organs such as nectar glands in some insectpollinated plants for example banana Musa spp. .Phloem StructurePhloem is a living tissue which consists of sieve tubes andcompanion cells. During cell differentiation and development ofsieve tubes, most of the cytoplasm is pushed towards the cell wallleaving a lumen filled with a slimy sap containing fine protein fibrils. The cross walls between adjacent sieve tubes are perforatedforming a sieve plate with pores . This allows continuous flow ofsubstances. The companion cell possesses a dense cytoplasm andprominent cell organelles. See figure 1.12. These cells havenumerous mitochondria which generate the energy required fortranslocation. The cytoplasmic filaments consists of fine proteinfibres. The filaments are continuous from one sieve tube to the nextvia the pores in the sieve plates. Materials are believed to bemoved either downwards or upwards along these filaments. Fig. 1.12: Phloem tissueStudy Question11. The rate of transpiration of maize plants was measured over a24-hour period in a farm in Kitale, Kenya and the following werethe results. Table 1.1Time of dayWater loss per hour cm3 7 am9 am11 am1 pm3 pm5 pm7 pm9 pm11 pm1 am3 am1323 a Plot the results on a graph. Place time on the x-axis. B Relate time of day to environmental factors. C Explain how the rate of transpiration varies within the 24hours.1.3 Transport in AnimalsThe Circulatory SystemLarge and complex animals have circulatory systems that consist oftubes, a transport fluid and some means of pumping the fluid or airwithin the tubes. A circulatory system transports the substances andmaintains a steep concentration gradient at the surfaces wherediffusion takes place.


Table 1.1Time of dayWater loss per hour cm3 7 am9 am11 am1 pm3 pm5 pm7 pm9 pm11 pm1 am3 am1323 a Plot the results on a graph. Place time on the x-axis. B Relate time of day to environmental factors. C Explain how the rate of transpiration varies within the 24hours.1.3 Transport in AnimalsThe Circulatory SystemLarge and complex animals have circulatory systems that consist oftubes, a transport fluid and some means of pumping the fluid or airwithin the tubes. A circulatory system transports the substances andmaintains a steep concentration gradient at the surfaces wherediffusion takes place. Such surfaces include the lungs and gills. Two types of circulatory systems exist in animals: open andclosed. In an open circulatory system the transport fluid iscontained in the general body cavity or coelom. This type ofsystem is common in invertebrates especially arthropods. There is atransporting fluid in a body cavity. The cavity is known ashaemocoel. A closed circulatory system on the other hand, isfound in vertebrates and annelids where the transporting fluid blood is conveyed in special tubes referred to as blood vessels. Comparison between Open and ClosedCirculatory SystemIn closed circulatory system, blood is pumped into closed vessels,hence generation of high pressure which causes the blood to flowfaster. Tissues receive their requirements at a faster rate andremoval of metabolic waste, is also faster. As a result, organismswith closed circulatory system are more active than those with opencirculatory where blood is pumped into the haemocoel thus loosingits pressure. In a closed circulatory system, blood is not in directcontact with the tissues as is the case in an open circulatory bloodsystem. Transport in InsectsInsects have an open circulatory systems where blood is containedin haemocoel and within a dorsal tubular heart. See figure 1.13. Theblood contains suspended leucocytes white blood cells and somepigments but it is not largely involved in the transport of oxygenand carbon dioxide. Transport of gases in insects is principally bydiffusion in the tubes called tracheal system as will be discussedlater in chapter 2.In a cockroach a typical insect there is a tubular heart justabove the alimentary canal.


See figure 1.13. Theblood contains suspended leucocytes white blood cells and somepigments but it is not largely involved in the transport of oxygenand carbon dioxide. Transport of gases in insects is principally bydiffusion in the tubes called tracheal system as will be discussedlater in chapter 2.In a cockroach a typical insect there is a tubular heart justabove the alimentary canal. The heart has thirteen chambers, threein the thorax and ten in the abdominal segments. The anteriorsegment is joined to the aorta that empties the blood into sinusesof the head. Each chamber contains a pair of valves at the anteriorpart, which prevent back flow of the blood. Each chamber has a pairof lateral openings called ostia which are closed AUTHOR to flow into the heart through the ostia but notout of it. Fig. 1.13: Open circulatory system in a cockroachThe NAME SystemA closed circulatory system is found in all vertebrates but is mostdeveloped in mammals where a powerful muscular heart pumpsblood into the arteries. The arteries divide into much smallervessels called arterioles which in turn divide into even much smallervessels called capillaries. Capillaries spread out in a networkfashion in the tissues. The capillaries eventually re-unite to formvenules that in turn form larger vessels called veins. The veins takeblood back to the heart. See figure 1.14 in page 20. NAME 6 a In this activity you will use figure 1.14 in page 20.1. Trace the path followed AUTHOR point until itreturns to the same point e.g. i Kidneys ii Liver iii Right arm. From the above activity you notice that blood flows into the hearttwice for every complete circulation. This is called the doublecirculation. Blood from the body tissues is pumped to the lungs and thenback to the heart. This is called pulmonary circulation. From theheart, blood is then pumped to the rest of the body organs. This iscalled systemic circulation. Mammals and birds have a four-chambered heart. The righttwo chambers deal with deoxygenated blood while the left twochambers deal with oxygenated blood.


From theheart, blood is then pumped to the rest of the body organs. This iscalled systemic circulation. Mammals and birds have a four-chambered heart. The righttwo chambers deal with deoxygenated blood while the left twochambers deal with oxygenated blood. Hence deoxygenated andoxygenated blood do not mix. Furthermore, blood is at a higher pressure since the heartpumps it twice. This enables the blood to flow faster to the tissues. These two advantages enable the birds and mammals to be moreactive. In some other animals e.g. fish, blood flows only once throughthe heart for every complete circuit. This is called single circulatorysystem. In such a circulatory, the heart has only one atrium andventricle. 2eSSES SOS cininionninge Nepal vinFig. 1.14: Mammalian circulationThe Structure and Function of the HeartExternal Structure of the HeartThe heart is a muscular organ located in the chest cavity inbetween the lungs. It pumps the blood to the whole body. Atranslucent membrane called pericardium encloses the heart. Thepericardial membrane secretes a fluid that acts as a lubricant whenthe heart is working. The outer part of the membrane is coveredwith a layer of fat that act as a shock absorber. This membrane alsohelps to keep the heart in position and check on over dilation of theheart. The heart is made up of special type of muscles calledcardiac muscles that contain interconnected muscle fibres. Thesemuscle fibres have their own blood supply through coronary artery. The coronary artery branches from the aorta just beyond the semilunar valves. It forms branches which run on the heart surface andinto the heart muscles before dividing into capillaries. Thecapillaries join up to form coronary vein which conveys blood to theright atrium. See figure 1.15. Fig. 1.15: External structure of the mammalian heartInternal Structure of the HeartThe mammalian heart is composed of four chambers. Two auricles atria form the upper chambers. They are thin-walled and smallerin volume than the lower chambers. The right auricle receive deoxygenated blood from the body organsexcept the lungs while left auricle receives oxygenated blood fromthe lungs through the pulmonary vein. The lower chambers are called ventricles and are composedof thick cardiac muscles.


Two auricles atria form the upper chambers. They are thin-walled and smallerin volume than the lower chambers. The right auricle receive deoxygenated blood from the body organsexcept the lungs while left auricle receives oxygenated blood fromthe lungs through the pulmonary vein. The lower chambers are called ventricles and are composedof thick cardiac muscles. The left ventricle has thicker cardiacmuscles than the right ventricle. The volume of the left ventricle issmaller than that of the right ventricle. A thick muscular wall calledthe interventricular septum separates the two ventricles. Betweenthe atria and the ventricles are atrio-ventricular valves whichprevent the blood from flowing back into the auricles when ventriclemuscles contract. These are right atrio-ventricular valve ortricuspid valve and left atrio-ventricular valve or bicuspid valve. These valves are supported AUTHOR cordae tendinae which areattached to the wall of the ventricles on each side. The tendonsprevent the atrio-ventricular valves from turning inside out whenunder pressure as the ventricles contract. At the base of pulmonary artery and aorta are cup like valvescalled semilunar valves. The valves are opened AUTHOR generated AUTHOR The valvesprevent backward flow of blood when the ventricles relax. Seefigure 1.16.Circulation in the HeartDeoxygenated blood from the body tissues except the lungs entersthe right auricle through the vena cava. It then flows to rightventricle via the tricuspid valve. When the right ventricle contracts,blood from the right ventricle is forced via the semilunar valvesthrough the pulmonary artery into the lungs. Blood from the leftventricle is forced to flow via the semilunar valves through the aortato the body tissues. Oxygenated blood from the lungs flow throughthe pulmonary vein to the left auricle via the bicuspid valve to theleft auricle. Fig.


Blood from the leftventricle is forced to flow via the semilunar valves through the aortato the body tissues. Oxygenated blood from the lungs flow throughthe pulmonary vein to the left auricle via the bicuspid valve to theleft auricle. Fig. 1.16: The internal structure of the mammalian heartPumping Mechanism of the HeartThe heart undergoes contraction systole and relaxation diastole rhythmically throughout the animal s life. Diastole Relaxation When ventricular muscles relax, the volume of each ventricleincreases, while pressure decreases. The atrio-ventricular valve orcuspid valve opens allowing deoxygenated blood from the bodytissues to flow into the right ventricle while oxygenated blood flowsfrom the left atrium into the left ventricle. The semilunar valvesclose preventing the blood from flowing back into the ventricles. The slight contractions of the auricles force the blood to flow intothe ventricles. Refer to figure 1.17 a which shows diastole on theleft side of heart. Fig. 1.17 a : Diastole ventricle relaxesSystole contraction When the ventricular muscles contract, the atrio-ventricular orcuspid valves close preventing the blood from flowing back into theauricles. The volume of the ventricles decreases while pressureincreases, to force blood out of the heart to the: i Lungs via the semilunar valve through the pulmonary artery. Ii Body tissues except the lungs via the semilunar valve throughthe aorta. The thick cardiac muscles of the left ventricle generate highpressure which forces the blood to the furthest tissue. A systole isalways followed AUTHOR two make a complete heartbeat. See figure 1.17 b .The heart contracts at an average of about 60 to 70 times perminute. High temperature and emotions can result in an increasedrate of the heartbeat. The heartbeat is faster in a child than in anadult. Heartbeats may be felt as pulse AUTHOR a fairlylarge artery, such as that at the wrist, against a bone. Fig.


High temperature and emotions can result in an increasedrate of the heartbeat. The heartbeat is faster in a child than in anadult. Heartbeats may be felt as pulse AUTHOR a fairlylarge artery, such as that at the wrist, against a bone. Fig. 1.17 b : Systole ventricle contractsHeartbeatThe heart is capable of contracting and relaxing rhythmicallywithout fatigue due to its special muscles called cardiac muscles. The cardiac muscle fibres are interconnected as shown in figure1.18 so that waves of contraction can travel throughout the mass ofthe muscle. Fig. 1.18: Structure of the cardiac muscleFig. 1.19: The electrical excitation that follows the contraction of the heartThe rhythmic contraction of the heart arise from within the heartmuscles without nervous stimulation. The contraction is thereforesaid to be myogenic. However, the heartbeat is initiated AUTHOR node SA . This is a small area of specialised cardiacmuscle fibres in the wall of right auricle. Its spontaneous rhythmicalelectrical activity initiates and maintains contractions of the heart heartbeat . However the rate of heartbeat is under nervouscontrol. The vagus nerve slows down the heartbeat where as thesympathetic nerve speeds up the heart beat. See figure 1.19.Structure and Function of Arteries, NAME main blood vessels are arteries, veins and capillaries. ArteriesThey originate from the heart and carry blood away from the hearte.g. Aorta carry oxygenated blood from the heart to all parts of thebody except the lungs while pulmonary artery carry deoxygenatedblood to the lungs. Arteries carry blood at high pressure and have a thick muscularwall to resist the pressure of the blood inside them. The innermostlayer of the artery is called endothelium which is composed of asingle layer of cells. This layer is found in all blood vessels. Itprovides a smooth lining which offers the least possible frictionalresistance to blood flow. The middle layer is composed of elasticfibres and smooth muscles.


This layer is found in all blood vessels. Itprovides a smooth lining which offers the least possible frictionalresistance to blood flow. The middle layer is composed of elasticfibres and smooth muscles. The outer layer is formed of elasticmuscular fibres collagen fibres as shown in figure 1.20 a .When ventricles contract systole , the muscular layer ofarteries relaxes stretching outwards to allow blood into the arteries. When ventricle muscles relax diastole , the muscular layercontracts, pressing inwards forcing the blood to flow forwards. Thisproduces the pulsating action in arteries. The muscular wall ofthe arteries is under the control of nerves and hormones which alterthe diameter of the arteries. This plays a major role in regulatingblood flow to the body organs. Fig.1.20 a : Structure of the arteryThe aorta forms branches which supply blood to major organsof the body. These branches divide to form small blood vesselscalled arterioles. The arterioles divide further to form the bloodcapillaries. CapillariesThey form one of the most important parts of the circulatorysystem. Capillaries are numerous and very close to the tissues insuch a way that each cell is near a blood capillary. Exchange ofsubstances between the tissues and the blood takes place acrossthe capillary wall. This is possible due to the fact that the walls ofcapillaries are made up of endothelial cells only that are only onecell thick. Thus provides the least distance for exchange ofsubstances within cells. Figure 1.20 b shows the structure of acapillary. Exchange of substances occurs AUTHOR in capillary beds as shown in figure 1.20 c . Branching ofarterioles into capillaries increases the surface area of thecapillaries and pressure of blood in them. This forces smallmolecules out of the blood within the capillaries to form part of thetissue fluid. The tissue fluid formed is similar to plasma incomposition except it lacks protein, red blood cells and someleucocytes. Phagocytic leucocytes squeeze in between the cells ofthe capillary wall and pass into the tissue fluid. From the tissuefluid, cells extract substances such as glucose, oxygen, amino acids,vitamins, hormones and mineral ions. Fig.


Phagocytic leucocytes squeeze in between the cells ofthe capillary wall and pass into the tissue fluid. From the tissuefluid, cells extract substances such as glucose, oxygen, amino acids,vitamins, hormones and mineral ions. Fig. 1.20 b : Portion of a capillary blood vesselUltra filtration results to a drop in pressure so that at thevenules and in the capillary bed, blood pressure is less than that ofthe tissue fluid. Substances from the tissue fluid pass back into thecapillaries AUTHOR back AUTHOR more concentrated than the tissue fluid. Carbon IV oxidepasses into the blood through diffusion. More tissue fluid passes intolacteal of the lymphatic system as shown in figure 1.20 c . Fig. 1.20 c : Relationship between capillaries, cells and lymphaticsThe venules join up to form large vessels called veins. VeinsVeins carry blood from all parts of the body back to the heart. Bloodpressure in the veins is very low hence the blood flows smoothly. The veins have relatively larger lumen as compared to the arteries. This offers minimum resistance to blood flow. The walls of the veinsare made up of thin muscles as shown in figure 1.20 d .Fig. 1.20 d : VeinsVeins have valves as shown in figure 1.20 e throughout theirlength, which prevent back flow of blood thus ensuring that bloodflows only towards the heart. Forward flow of blood in veins is assisted AUTHOR veins are located in between the skeletal muscles. When the muscles contract they press the veins forcing the bloodflow towards the heart. This explains the need for physicalexercises. All veins carry deoxygenated blood with fewer nutrientsbut more nitrogenous waste and other metabolic wastes except: a Renal vein that carries blood from the kidney wherenitrogenous waste, some water and salts has been removed. B Hepatic portal vein that carries blood rich in dissolved foodsubstances from the gut to the liver. C Pulmonary vein that carries oxygenated blood from the lungsto the left auricle of the heart. NAME of the BodyFigure 1.21 illustrates major arteries which supply blood to someorgans of the body and major veins which collect blood from theorgans. Fig.1.20 e : Valves in veinsFig.


This explains the need for physicalexercises. All veins carry deoxygenated blood with fewer nutrientsbut more nitrogenous waste and other metabolic wastes except: a Renal vein that carries blood from the kidney wherenitrogenous waste, some water and salts has been removed. B Hepatic portal vein that carries blood rich in dissolved foodsubstances from the gut to the liver. C Pulmonary vein that carries oxygenated blood from the lungsto the left auricle of the heart. NAME of the BodyFigure 1.21 illustrates major arteries which supply blood to someorgans of the body and major veins which collect blood from theorgans. Fig.1.20 e : Valves in veinsFig. 1.20: Major blood vessels of the human bodyTable 1.2: Differences between arteries and veinsArteriesVeins1. Walls are thick muscular andelastic.1. Walls thin less muscularand elastic .2. Have no valves except at thebase of large arteries leavingthe heart.2. Have valves at intervalsthroughout their length.3. Blood flows rapidly in pulses.3. Blood flows smoothly.4. Blood flows rapidly underpressure.4. Blood flows slowly underlow pressure.5. Tend to lie deeper in the body.5. Tend to lie near the bodysurface.6. Transport oxygenated bloodexcept pulmonary artery.6. Transport deoxygenatedblood except pulmonaryvein.7. Narrow lumen.7. Wider lumen. The photomicrograph 1.3 shows some of these differences. NAME 6 b To display the circulatory system in a mammalRequirementsFreshly killed rats or rabbits , dissecting board or tray, dissectingpins, scissors, scalpels, forceps, hand lens, cotton wool and water. Procedure1. Dissect the mammal using the procedure in the dissecting guideand conduct the following: i Display the heart, lungs, liver, kidneys and the spleen. Ii Identify the coronary, carotids, jugular, renal, hepaticarteries and veins. Iii Trace the dorsal aorta and the posterior vena cava towardsand away from the heart. Similarly trace the anterior orinferior vena cava from the anterior region of the animalnoting its entry into the right atrium. Plate 1.3: T.S.


Dissect the mammal using the procedure in the dissecting guideand conduct the following: i Display the heart, lungs, liver, kidneys and the spleen. Ii Identify the coronary, carotids, jugular, renal, hepaticarteries and veins. Iii Trace the dorsal aorta and the posterior vena cava towardsand away from the heart. Similarly trace the anterior orinferior vena cava from the anterior region of the animalnoting its entry into the right atrium. Plate 1.3: T.S. of an artery and vein of a human being2. Draw and label the transport system of the animal as displayedin the dissection. Study Questions12. Compare the physical appearances of the arteries and veinsgiving reasons for your observations.13. Name the blood vessels that convey blood to: i the brain ii the fore limb iii the lungs iv the liver v the kidneys vi the hind limb.14. What are the functions of the dorsal aorta and the vena cava? NAME 7To investigate the external and internal structures of amammalian heartRequirementsFresh heart from a mammal such as cow, sheep, goat or pig,dissecting board or tray, dissecting pins, scissors, scalpel, forceps,hand lens and cotton wool. Procedure1. Examine the external features of the provided heart payingparticular attention to: i Its shape and thickness of its wall. Ii The remains of the blood vessels on its upper side. Iii Identify the atria and the ventricles. Iv Identify the coronary blood vessels on the outer walls ofthe heart.2. Dissect the heart to expose its internal structure. Carefullyexamine these structures to identify: i The chambers of the heart. Ii The muscular walls of the atria and ventricles. Iii The heart valves: bicuspid, tricuspid and semi-lunar valves. Iv The coronary blood vessels on the inner walls of the heart. V The remains of the vena cava, pulmonary vein and arteryand the aorta. Carefully note where these enter or leave theheart. Study Questions15. Draw and label the external structures of the heart.16. Draw and label the internal structures of the heart.


Carefully note where these enter or leave theheart. Study Questions15. Draw and label the external structures of the heart.16. Draw and label the internal structures of the heart. Show witharrows the direction of blood flow through the heart. NAME 8To investigate pulse rate at the wristRequirementsStop watches or clocks. Procedure1. Locate the radial, artery in the wrist at the base of the thumb ofa subject.2. Place the index and middle fingers on the radial pulse and notethe pulsating effect of blood flow in the artery.3. Start the stopwatch and count how many times the bloodpasses through the radial artery.4. Record the number of blood pulses for a one-minute time lapse.5. Repeat the count three times and enter the readings as in table1.3.6. Run round the laboratory block and return to the laboratory.7. Locate the pulse and record its rate after the exercise. Table 1.3: Pulse rateStudy Questions17. From the readings in the table above draw conclusions on thepulse rate of the subject.18. How does exercise affect the pulse rate?19. Suggest the origin of the pulse in the arteries and its effect ingeneral blood circulation. NAME 9To investigate the direction of blood flow in the superficialveins of the armsRequirementsBandage or bandsProcedure1. Select volunteers with large visible veins in the arm.2. Firmly tie the bandage or a band around the upper arm abovethe elbow of the subject.3. Use the index and middle fingers to locate a suitable stretch ofa vein that is not branched such as the radial vein of the arm.4. Gently press the index finger on this vein or any prominent veinat a given point.5. Note any observable changes on the vein.6. Using the middle finger stroke the vein pushing the bloodupwards towards the elbow.7. Release the pressure on the vein and note what happens to theblood flow.8. Stroke the vein this time pushing the blood downwards towardsthe hand.9. Note any effects on the flow of blood when this is done. Study Questions20. What happens when a bandage or band is tied around the armof the subject?21. How is the blood flow affected after the first stroke in step 6?Give reasons for this. Diseases and Defects of Circulatory SystemThrombosisThis refers to formation of a clot in the blood vessels.


Note any effects on the flow of blood when this is done. Study Questions20. What happens when a bandage or band is tied around the armof the subject?21. How is the blood flow affected after the first stroke in step 6?Give reasons for this. Diseases and Defects of Circulatory SystemThrombosisThis refers to formation of a clot in the blood vessels. The mostcommon of all is the coronary thrombosis that leads to blockageof coronary artery which supplies blood to the heart. The blockage may be due to arteries becoming increasinglyfibrous or accumulation of fatty materials on the artery walls. Thesubsequent narrowing of coronary artery results in less bloodflowing to the heart. Insufficient oxygen therefore, reaches theheavy oxygen dependent heart muscles. A serious blockage of theartery can result into fatal heart attack. Coronary thrombosis maybe caused AUTHOR which results to high amount ofcholesterol in the blood. Cholesterol accumulates in the coronaryarteries blocking the associated blood vessels thus causing lessoxygen to reach the heart muscles. Other causes may be heavyintake of alcoholic drinks, smoking, overweight, psychological andemotional stress. Practising healthy lifestyles can control coronary thrombosis. ArteriosclerosisArteriosclerosis refers to the deposition of calcium in the walls ofthe blood vessels. It leads to hardening of the arteries which resultto permanent change in arterial wall. This leads to thickening andloss of elasticity of the vessel wall. The most common type ofarteriosclerosis is characterised AUTHOR tissue in the wall of the arteries. The cause of thedisease is not clearly known, however medical scientists haveestablished some relationship between the disease and overweight,lack of exercise and emotional stress. Taking drugs that reduce cholesterol in the blood can controlarteriosclerosis. Physical exercises can also reduce chances ofarteriosclerosis since the excess fat will be broken down while theheart is kept active and strong. Varicose VeinsIt is a condition in which the superficial veins especially at the backof the legs become swollen and flabby due to failure of some valvesto function properly. This results in the retention of tissue fluid. Thedisease can be controlled AUTHOR the body. Hypertension or NAME PressureNormal blood pressure varies between 90 60 and 140 90 mm ofmercury.


Physical exercises can also reduce chances ofarteriosclerosis since the excess fat will be broken down while theheart is kept active and strong. Varicose VeinsIt is a condition in which the superficial veins especially at the backof the legs become swollen and flabby due to failure of some valvesto function properly. This results in the retention of tissue fluid. Thedisease can be controlled AUTHOR the body. Hypertension or NAME PressureNormal blood pressure varies between 90 60 and 140 90 mm ofmercury. The numerator refers to systolic pressure duringcontraction and the denominator refers to diastolic pressure duringrelaxation. High blood pressure is a disorder that is associated withheavy drinking, smoking, taking of large quantities of salt in thefood and general body stress. High blood pressure may also becaused AUTHOR heart to generate highpressure that force the blood through the less elastic vessels. The heart of a hypertensive person is therefore overworked andthe person is prone to heart failure. Hypertension may lead tobursting of arteries and capillaries. If the blood vessels in the brainbursts, a stroke results and the brain cells die in the affected areas. Paralysis at least for some parts of the body, usually accompanies astroke. Some strokes are fatal. This disorder is more common in individuals aged above 40 years. Hypertension can be controlled by: i Having regular exercises. Ii Intake of less salt. Iii Avoiding excessive drinking of alcoholic beverages. Iv Not smoking cigarettes and other related drugs. V Avoiding general body stress AUTHOR give individuals peace of the mind. NAME and Functions of BloodComposition of BloodThe mammalian blood consists of fluid medium called plasma withcellular components suspended in it. These cellular components areerythrocytes red blood cells , leucocytes white blood cells andnon-nucleated thrombocytes platelets .The PlasmaPlasma is a pale yellow fluid consisting mainly of 90 per cent waterin which a variety of substances are suspended and othersdissolved. Substances in plasma include glucose, mineral salts,hormones, some enzymes, amino acids and lipids. Also found in theplasma are plasma proteins such as anti-bodies, albumin, fibrinogenand waste products of metabolism such as carbon IV oxide andurea.


These cellular components areerythrocytes red blood cells , leucocytes white blood cells andnon-nucleated thrombocytes platelets .The PlasmaPlasma is a pale yellow fluid consisting mainly of 90 per cent waterin which a variety of substances are suspended and othersdissolved. Substances in plasma include glucose, mineral salts,hormones, some enzymes, amino acids and lipids. Also found in theplasma are plasma proteins such as anti-bodies, albumin, fibrinogenand waste products of metabolism such as carbon IV oxide andurea. Blood plasma from which fibrinogen and cells have beenremoved is called serum. The main functions of plasma are: i Transports red blood cells which contain oxyhaemoglobin tothe tissues hence facilitate transport of oxygen. Ii Forms the main medium in which dissolved food substancesare transported to the liver and then to the other body tissues. Iii Transports metabolic wastes such as urea carbon IV oxideand other nitrogenous wastes to the excretory organs wherethey are eliminated from the body such organs include kidneys,lungs and the skin. Iv Transportation of hormones. V Oxygen and carbon IV oxide are slightly soluble in water. Hence the plasma transports small amount of these gases. Vi Regulation of pH of the body fluids. Vii Distributes heat around the body hence regulate bodytemperature. NAME Erythrocytes In an adult the red blood cells are made in the bone marrow of theshort bones such as the sternum, ribs and the vertebrate. In theembryo they are made in the liver and spleen. Mature red bloodcells have no nuclei but have a sunken centre that makes the cellresemble a biconcave disc as shown in figure 1.22 a and b . Theabsence of a nucleus leaves room for more haemoglobin to bepacked in the cell to enable it to carry more oxygen. Haemoglobin isa protein which contains iron and readily combines with oxygen toform an unstable compound known as oxyhaemoglobin. Red bloodcells carry oxygen in the form of oxyhaemoglobin. The haemoglobin has high affinity for oxygen. It readily picksup oxygen in the lungs where the concentration is high and easilyreleases oxygen in the tissues where the concentration is low. In the tissues, oxyhaemoglobin readily breaks down dissociates into haemoglobin and oxygen.


Red bloodcells carry oxygen in the form of oxyhaemoglobin. The haemoglobin has high affinity for oxygen. It readily picksup oxygen in the lungs where the concentration is high and easilyreleases oxygen in the tissues where the concentration is low. In the tissues, oxyhaemoglobin readily breaks down dissociates into haemoglobin and oxygen. The oxygen diffuses outof the red blood cells and through the capillary walls into thetissues. The haemoglobin is then free to pick up more oxygenmolecules from the lungs. Fig.1.22: Red blood cellsRed blood cells are about five million per cubic millimetre ofblood. Due to their ability to change their shape, they are capableof squeezing through the narrow capillaries. Their large numbersand shape make them suitable for their function. The biconcaveshape increases their surface area over which gaseous exchangecan take place. Red blood cells have a life span of about four months afterwhich they break down and disintegrate in the liver and the spleen. The iron released from the breakdown of the old red blood cells isused in the manufacture of new cells. Although one per cent of allthe red blood cells is used in the manufacture of new ones daily,their number per cubic millimetre remains fairly constant in theblood of a healthy person. In the case of people living in high altitudes, the body respondsto the low oxygen concentration AUTHOR ofred blood cells and the haemoglobin content in them. This responseincreases the oxygen carrying capacity of the red blood cells. Besides oxygen, haemoglobin can readily combine with carbon II oxide carbon monoxide to form carboxyhaemoglobin. Thiscompound does not readily dissociate and therefore reduces thecapacity of haemoglobin to transport oxygen to the tissues. Carbon II oxide is therefore a respiratory poison which can be fatal ifbreathed in for a considerable length of time. Burning charcoalstoves, jikos in a poorly ventilated room produces carbon II oxide. Exhaust fumes from vehicles also contain carbon II oxide. Itis important therefore that charcoal stoves are not allowed to burnin poorly ventilated rooms because carbon II oxide canaccumulate to levels dangerous to life. In addition to transport of oxygen red blood cells also transportabout 95 percent of carbon IV oxide.


Burning charcoalstoves, jikos in a poorly ventilated room produces carbon II oxide. Exhaust fumes from vehicles also contain carbon II oxide. Itis important therefore that charcoal stoves are not allowed to burnin poorly ventilated rooms because carbon II oxide canaccumulate to levels dangerous to life. In addition to transport of oxygen red blood cells also transportabout 95 percent of carbon IV oxide. Here the enzyme carbonicanhydrase speeds up the conversion of carbon IV oxide to weakcarbonic acid. The carbonic acid dissociates into hydrogencarbonate and hydrogen ions. The hydrogen carbonate ions diffuseout of the red blood cells into the plasma in which it is thentransported to the lungs. The remaining 5 percent of carbon IV oxide is transported as dissolved carbon IV oxide in the plasma. NAME cells Leucocytes Unlike red blood cells, white blood cells are nucleated, they lackhaemoglobin and hence their cytoplasm is colourless. They arefewer in number than the red blood cells. There are about 7,000leucocytes per cubic millimetre of blood. In an average healthyman, there are about 600 red blood cells to every leucocyte cell. However their number increases greatly during infection. They areformed in the bone marrow of long bones and lymph nodes. Theirfunction is to protect the body against pathogenic micro-organismssuch as bacteria, protozoa, viruses and their secretions. Leucocytes are of two main types: granulocytes andagranulocytes. Granulocytes are also called phagocytes orpolymorphs. They have lobed nuclei and granulated cytoplasm. See figure 1.23.Granulocytes use amoeboid movement to pass through thewalls of the capillaries into the affected tissues. In the tissues andblood, the granulocytes engulf pathogenic micro-organisms AUTHOR the name phagocyte. Onceingested, the micro-organism are digested. Some white blood cellsmay die in the course of phagocytosis.


In the tissues andblood, the granulocytes engulf pathogenic micro-organisms AUTHOR the name phagocyte. Onceingested, the micro-organism are digested. Some white blood cellsmay die in the course of phagocytosis. The dead phagocytestogether with dead micro-organisms and damaged tissues form pus. The agranulocytes assist the phagocytes to destroy the pathogenicmicro-organisms. Agranulocytes on the other hand have rounded or bean-shapednuclei and lack granules in their cytoplast. They consist ofmonocytes and lymphocytes. The lymphocytes are formed in the lymph nodes and produceantibodies that protect the body from infection in the followingways: i Antibodies which are antitoxins neutralise the toxins antigens produced AUTHOR 1.23: Types of Leucocytes ii Some antibodies such as agglutinins cause clumping togetherof micro-organisms. This stops the microorganisms frommultiplying and eventually they die. In this way they areingested AUTHOR iii Lysins destroy micro-organisms AUTHOR walls. Iv Opsonins are antibodies which adhere to the outer surface ofmicro-organisms thus making it easier for phagocytes to ingestthem. The antibodies are produced when micro-organismsinvade the body. After recovery from infection the level ofantibodies decreases gradually as they disintegrate. Seeimmune response .Platelets Thrombocytes Platelets are fragments from large cells in the bone marrow. Theyare discoid in shape and assume a star-shaped appearance inextracted blood. Their number is approximately 2.5 million per mm3of blood. They have no nucleus and play an important role in bloodclotting when blood vessels are injured. See figure 1.24.Fig. 1.24: PlateletsA blood smear observed under a microscope reveals the variouscomponents of blood. See photomicrograph in plate 1.4.Plate 1.4: Human blood smear courtesy of KEMRI NAME ProcessThe process of clotting involves a series of complex reactions wheresoluble blood protein is converted into a mass of tangled threads ofinsoluble protein.


See figure 1.24.Fig. 1.24: PlateletsA blood smear observed under a microscope reveals the variouscomponents of blood. See photomicrograph in plate 1.4.Plate 1.4: Human blood smear courtesy of KEMRI NAME ProcessThe process of clotting involves a series of complex reactions wheresoluble blood protein is converted into a mass of tangled threads ofinsoluble protein. This process begins when blood vessels aredamaged. When blood vessels are injured, platelets exposed to airrupture on damaged tissues to release thromboplastin enzymethrombokinase which initiates the clotting process. Thromboplastinneutralises heparin an anti-clotting factor and activatesprothrombin to thrombin. This process requires calcium ions. Thrombin activates conversion of fibrinogen to fibrin which forms ameshwork of fibres, on the cut surface to trap red blood cells toform a clot. The clot dries up to form a scab that stops the bleedingand protects the damaged tissues from infection. Figure 1.25 showssimplified flow chart summarising the process of blood clotting. Thus blood clotting reduces loss of blood when blood vesselsare injured. Excessive loss of blood especially more than 2 litres canlead to severe anaemia unless corrected immediately AUTHOR 1.25: Simplified flow diagram showing the process of blood clottingIt is important to note that fibrinogen is only changed to fibrinwhen blood vessels are injured. Otherwise if this happens in vesselsthat are not injured, it would block up the blood vessels leading todeath. However, this does not happen because fibrinogen is notchanged to fibrin AUTHOR In undamagedvessels, blood does not contain thrombin but its inactive form calledprothrombin. Formation of prothrombin requires vitamin K.Undamaged vessels contain heparin which prevents conversion ofprothrombin to thrombin and neutralises any thrombin which maybe formed accidentally. Blood GroupsRed blood cells have certain proteins called antigens on theirplasma membrane. There are two of these antigens, designated Aand B. Blood groups are determined AUTHOR presentin an individual s red blood cell. Thus an individual whose red bloodcells have antigen A is grouped as A.


There are two of these antigens, designated Aand B. Blood groups are determined AUTHOR presentin an individual s red blood cell. Thus an individual whose red bloodcells have antigen A is grouped as A. Antigen B is grouped as B.Antigen A and B is grouped as AB while that without antigens isgrouped as O type. The plasma too has proteins called antibodies. There are twotypes of antibodies designated a and b. If an individual has antigenA blood group A on his her red blood cells, he she cannot haveantibody a in his her plasma, but will have antibody b . Similarly anindividual with antigen B blood group B has antibody a in his herplasma. This is due to the fact that agglutination or clumping of redblood cells takes place if antibodies corresponding to the antigencome into contact. See table 1.4.Table 1.4: Blood groups, antigens and antibodiesBlood groupAntigen in red blood cellsAntibody in plasmaAAbBBaABA and BNoneONone neither A nor B Both a and bBlood transfusionBlood transfusion is the transfer of blood from a donor to thecirculatory system of the recipient. A recipient will receive bloodfrom a donor if the recipient cannot produce antibodiescorresponding to the donor s antigens. Otherwise agglutination clumping together of the recipient s red blood cells will take place. Table 1.5 gives a summary of blood types and reactions of the bloodtypes. Table 1.5: Reactions of blood typesKey:Capital letter: Antigens blood groups Small letter: Antibodies Compatible no agglutination X Not compatible agglutination Note: Blood group AB has neither antibody a nor b. Indviduals withblood group AB can receive blood from all others. They aretherefore refered to as universal recipient. On the other hand,individuals with blood group O can donate blood to all others. Thischaracteristic leads to individuals with this blood group being calleduniversal donor. Study Questions22. From the above table identify the universal donor and theuniversal recipient. 23. Why is it important to screen blood before transfusion?A doctor must ensure that before one donates blood he she ishealthy and is between 18 and 65 years of age.


From the above table identify the universal donor and theuniversal recipient. 23. Why is it important to screen blood before transfusion?A doctor must ensure that before one donates blood he she ishealthy and is between 18 and 65 years of age. A drop of thedonor s blood is first tested to find out what group he she belongsto. Half a litre of the donor s blood is taken from a vein in the armand drained into a clean plastic bag to which an anti-coagulant hasbeen added, to stop clotting. The donor is given a drink to help topup blood volume and is advised to eat a balanced diet thereafter. The donated blood is kept in a blood bank at a temperature justabove freezing point for not more than one month. Donating bloodis good because it helps save lives. Healthy people should feel freeto donate blood regularly. The blood is normally not used for transfusion after one monthbecause most of the red blood cells will have died. Before bloodtransfusion is carried out, it is important that the blood is screenedfor pathogens such as NAME AcquiredImmuno- NAME HIV AIDS and compatibility. In addition to the A and B antigens, there is another antigen onthe red blood cells known as the Rhesus factor. People whoseblood contains this antigen are described as rhesus positive Rh ve while those who lack it are referred to as rhesus negative Rh ve . NAME ve blood is given Rh ve recipient, the latter responds byproducing the corresponding rhesus antibodies and nothing furtherhappens. But if the same recipient is given another dose of Rh veblood in a period of less than two weeks agglutination of red bloodcells occurs. In a case where a Rh ve mother bears a Rh ve baby,fragments of the foetus red blood cells containing the rhesusantigen pass across the placenta and get into the mother s bloodstream. The mother s red blood cells respond AUTHOR turn pass across the placenta into the blood ofthe foetus red blood cells before the foetus birth. This reaction iscommon after the first born and affects the foetus of thesubsequent pregnancies. This is as a result of the antigen-antibodyreaction taking place on the surface of the red blood cells.


The mother s red blood cells respond AUTHOR turn pass across the placenta into the blood ofthe foetus red blood cells before the foetus birth. This reaction iscommon after the first born and affects the foetus of thesubsequent pregnancies. This is as a result of the antigen-antibodyreaction taking place on the surface of the red blood cells. Thiscondition is referred to as haemolytic disease of the new-born Erythroblastosis foetalis . The new born baby can be saved byreplacing its blood with Rh ve blood. With every successivepregnancy the antibody level increases in the blood stream of themother and subsequent foetuses, if the baby is also Rh ve he shewill suffer from serious haemolytic disease of the new born. Withthe advancement in technology, it is possible to transfuse blood tothe foetus when still in the mother s womb and save the child. In recent years, it has also been found that the haemolyticdisease of the new-born can be prevented AUTHOR anti-rhesus globulin which coats the surfaces of red bloodcells thus preventing the antigen-antibody reactions. NAME 10Complete the table below AUTHOR your classmatesTable 1.6: Blood groupsStudy Question24. Name the dreaded disease associated with blood transfusion. Lymphatic SystemAnimals particularly vertebrates have an additional transport systembesides the blood system. This is known as lymphatic system andit supplies all the regions of the body just like blood system. Thelymphatic system is made of narrow, thin walled tubes known aslymph vessels which branch to form lymph capillaries in which afluid known as lymph is transported. See figure 1.26.Fig.1.26: Lymphatic SystemLymphThis is a fluid similar to blood plasma except that it contains lessproteins. It is formed as a result of ultra-filtration of blood from thenarrow blood capillaries. As blood circulates it reaches the bodytissues through the blood capillaries that form a network throughoutthe tissues. The pumping force from the heart together with thenarrow lumens of the capillaries exert a high pressure that forcesthe fluid part of the blood to filter out of the capillary walls into thesurrounding tissues.


It is formed as a result of ultra-filtration of blood from thenarrow blood capillaries. As blood circulates it reaches the bodytissues through the blood capillaries that form a network throughoutthe tissues. The pumping force from the heart together with thenarrow lumens of the capillaries exert a high pressure that forcesthe fluid part of the blood to filter out of the capillary walls into thesurrounding tissues. This filtrate consists of all the constituents ofblood plasma except the blood cells and the proteins. This isbecause the blood cells and proteins are too large to filter out of thecapillary walls. The fluid is known as tissue fluid or intercellularfluid. Once formed the tissue fluid bathes the cells of the tissuessupplying them with oxygen, food and other useful substances. The cells absorb these substances and pass out carbon IV oxide and other waste products in exchange. Most of the tissue fluidthen returns to the blood system through the venule end of thecapillaries. This is due to the lower hydrostatic pressure of the bloodat the venule and compared to that at the arteriole end of thecapillary. The excess tissue fluid, however, drains into the lymphvessels where it is known as lymph. The lymph glands produce antibodies and lymphocytes. Immune responsesImmune responses are reactions of the body that are as a result ofintroduction of antigens. They involve the production of antibodiesor leucocytes which combine with antigens. An antibody is achemical substance, usually a protein, which is formed in the bloodwhen an antigen is introduced into the tissue of a human being orany other animal. An antibody has a chemical composition which iscomplimentary to the antigen against which it reacts. This meansthat a particular antibody combines with or responds only to aparticular antigen to make it harmless. Antibodies are produced AUTHOR 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 NAME Natural immunity is inherited and controlled.


This meansthat a particular antibody combines with or responds only to aparticular antigen to make it harmless. Antibodies are produced AUTHOR 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 NAME Natural immunity is inherited and controlled. This trait can betransmitted from parent to offsprings. NAME or Artificial ImmunityAcquired immunity can either be naturally or artificially induced. When attacked AUTHOR , 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 AUTHOR 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 AUTHOR 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 AUTHOR , 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 AUTHOR 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 AUTHOR 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. NAME 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 AUTHOR Theattenuated bacteria or viruses stimulate the production of specificantibodies AUTHOR 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.


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 AUTHOR , 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. NAME 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 AUTHOR 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 AUTHOR 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 AUTHOR 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 AUTHOR 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 AUTHOR ? 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 AUTHOR ? 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 AUTHOR oxygen and carbon IV oxide are passed across the respiratory surface is known asgaseous exchange. This is brought about AUTHOR between the body of living organisms and thesurrounding medium. In simple organisms, oxygen is absorbed bythe exposed surface of the body AUTHOR 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 NAME 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 NAME 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. NAME 1 a To investigate the release of carbon IV oxide AUTHOR 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 AUTHOR 3. Why are boiling tubes covered with aluminium foil? NAME 1 b To investigate the release of oxygen AUTHOR , 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 AUTHOR 3. 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 AUTHOR 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 AUTHOR 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 AUTHOR 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 AUTHOR 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 AUTHOR 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 NAME 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 AUTHOR 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 AUTHOR 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 AUTHOR Theseopenings permit gaseous exchange to take place between theinterior of the plant and the outside AUTHOR 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 NAME 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 AUTHOR ,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. NAME 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 AUTHOR membrane. Oxygen dissolved in the surrounding water, diffuses across themembrane into the cytoplasm.