Biology S2_0 PDF - South Sudan National Curriculum

 How to take care of your books. Do’s ! ! 1. Please cover with plastic or paper. (old newspaper or magazines) 2. Please make sure you have clean hands before you use your book. 3. Always use a book marker do not fold the pages. 4. If the book is damaged please repair...

 How to take care of your books. Do’s ! ! 1. Please cover with plastic or paper. (old newspaper or magazines) 2. Please make sure you have clean hands before you use your book. 3. Always use a book marker do not fold the pages. 4. If the book is damaged please repair it as quickly as possible. 5. Be careful who you lend your schoolbook to. 6. Please keep the book in a dry place. 7. When you lose your book please report it immediately to your teacher. Don’ts 1. Do not write on the book cover or inside pages. 2. Do not cut pictures out of the book. 3. Do not tear pages out of the book. 4. Do not leave the book open and face down. 5. Do not use pens, pencils or something thick as a book mark. 6. Do not force your book into your schoolbag when it is full. 7. Do not use your book as an umbrella for the sun or rain. 8. Do not use your book as a seat. FOREWORD I am delighted to present to you this textbook, which is developed by the Ministry of Gen- eral Education and Instruction based on the new South Sudan National Curriculum. The National Curriculum is a learner-centered curriculum that aims to meet the needs and aspirations of the new nation. In particular, it aims to develop (a) Good citizens; (b) success- ful lifelong learners; (c) creative, active and productive individuals; and (d) Environmentally responsible members of our society. This textbook, like many others, has been designed to contribute to achievement of these noble aims. It has been revised thoroughly by our Subject Panels, is deemed to be fit for the purpose and has been recommended to me for approval. Therefore, I hereby grant my approval. This textbook shall be used to facilitate learning for learners in all schools of the Republic of South Sudan, except international schools, with effect from 4th February, 2019. I am deeply grateful to the staff of the Ministry of General Education and Instruction, es- pecially Mr Michael Lopuke Lotyam Longolio, the Undersecretary of the Ministry, the staff of the Curriculum Development Centre, under the supervision of Mr Omot Okony Olok, the Director General for Quality Assurance and Standards, the Subject Panelists, the Cur- riculum Foundation (UK), under the able leadership of Dr Brian Male, for providing profes- sional guidance throughout the process of the development of National Curriculum and school textbooks for the Republic of South Sudan since 2013. I wish to thank UNICEF South Sudan for managing the project funded by the Global Partnership in Education so well and funding the development of the National Curriculum and the new textbooks. I am equally grateful for the support provided by Mr Tony Calderbank, the former Country Director of the British Council, South Sudan; Sir Richard Arden, Senior Education Advisor of DfID, South Sudan. I thank Longhorn and Mountain Top publishers in Kenya for working closely with the Ministry, the Subject Panels, UNICEF and the Curriculum Foundation UK to write the new textbooks. Finally, I thank the former Ministers of Education, Hon. Joseph Ukel Abango and Hon. Dr John Gai Nyuot Yoh, for supporting me, in my previous role as the Undersecretary of the Ministry, to lead the Technical Committee to develop and complete the consultations on the new National Curriculum Framework by 29 November 2013. The Ministry of General Education and Instruction, Republic of South Sudan, is most grateful to all these key stakeholders for their overwhelming support to the design and development of this historic South Sudan National Curriculum. This historic reform in South Sudan’s edu- cation system is intended to benefit the people of South Sudan, especially the children and youth and the future generations. It shall enhance the quality of education in the country to promote peace, justice, liberty and prosperity for all. I urge all Teachers to put this textbook to good use. May God bless South Sudan. May He help our Teachers to inspire, educate and transform the lives of all the children and youth of South Sudan. Deng Deng Hoc Yai, (Hon.) Minister of General Education and Instruction, Republic of South Sudan Are you able to describe the movement Now study the picture below. What can of substances across the cell? This unit you see? What does this tell you about will focus on photosynthesis and plant plant nutrition? nutrition. Fig. 1.2: Photosynthesis process The picture above shows a growing 1.1 Photosynthesis plant. Plants require food in order to Unlike animals which consume the survive. Life of every organism depends already manufactured food, green on the food that we eat. This food can plants manufacture their own food. The be used for various processes in the body process by which green plants make such as provision of energy for work, their own food from simple inorganic growth and development, repair of substance using energy from sunlight worn out tissues and reproduction. The is known as photosynthesis. Plants are chief source of all energy is the sun. The able to convert light energy into a form process by which living organisms use that can be used by living organisms. food in the body is known as nutrition. The process takes place in plant leaves in Plants are able to synthesise their food a cellular structure called chloroplast. from simple substance, they are known as autotrophs. Lamella Grana/Granum Inner made up of membrane thylakoids Stroma Outer membrane Inter membrane space Starch granules Fig. 1.3: Structure of chloroplast 2  Sodium hydroxide Plant A Fig. 1.4: Results on test for need for light during photosynthesis The area under the foil or paper did not change colour to blue black because Sodium there was no starch present. The part of hydrogen the plant not covered with the foil on carbonate testing with iodine, it appeared blue- black. This is because starch was present. This part of the leaf act as a control. Plant B Activity 1.3: Is carbon dioxide needed for photosynthesis? Study questions Work in group of four 1. Explain the role of sodium Materials hydroxide and sodium hydrogen carbonate? Two potted plants kept in the 2. What was the result of testing the dark for 24hours, ink, transparent leaf in set-up A and B for starch? plastic bags, sodium hydroxide, oil, rubber band, methylated spirit, 3. Which set-up acts as the control beaker with water, boiling tube, experiment? Explain. sodium hydrogen carbonate(sodium bicarbonate), stone Were your steps the same as the one Procedure below? 1. Choose the correct materials that 1. Plant A: Put sodium hydroxide or you will need in investigating if potassium hydroxide into a small carbon dioxide is necessary for plastic container. Place it carefully photosynthesis. on the soil holding the plant. Take 2. Come up with the steps and how the transparent polythene bag you will show that carbon dioxide and cover the whole plant with it. is necessary for photosynthesis. Secure the bottom by tying it with Follow the steps to do the activity. one or two elastic bands. 3. The picture below will guide you. 5 form starch. This part will turn iodine 2H2O + light 4H + O2 from brown to blue-black. Chlorophyl Water Hydrogen Oxygen The white part has cells that do not have atom chlorophyll. These cells will not carry out photosynthesis, so no starch will be Photolysis formed. The starch test will be negative. ii) Some of the absorbed sunlight The green part of the leaf acts as a energy is stored. This energy will control experiment because it has all the conditions required for photosynthesis. also be used in the dark stage. b) Dark stage Is the second phase of photosynthesis which occurs in stroma and it takes place at the same time that the light stage is taking place in the grana. Carbon dioxide diffuses into stroma from the cell cytoplasma. The hydrogen from the Fig. 1.5: Variegated leaf light stage combines with carbon dioxide to form glucose. This process uses the Stages of photosynthesis energy stored during the light stage. The Photosynthesis occurs through a series manufacture of a carbohydrate (glucose) of chemical reactions. These reactions from carbon dioxide is called carbon can be divided into two main stages. dioxide fixation. The first stage requires light and is called the light stage. The second stage does CO2(g) + 4[H] [(CH2O)n] not require light and is called the light Carbon Hydrogen Simple energy and is called dark stage. dioxide atom carbohydrate a) Light stage It takes place in the grana. During this Carbon dioxide fixation stage, chlorophyll absorbs light energy. This energy is used in two ways. It is important to note that photosynthesis only avails carbohydrates to a plant. i) Some is used to split water Carbohydrates are important sources of molecules into hydrogen and energy to living organisms. However, a ox y ge n. T h is is k now n as plant needs proteins as well in order to photolysis of water. The hydrogen grow and develop and a variety of other is used in the dark stage. Some mineral nutrients for various chemical of the oxygen formed is released reactions to take place in its cells. A plant from the leaf through the stomata. obtains mineral salts from the soil by The rest is used up in the plant active transport or diffusion through its cells for respiration. root hairs. Examples of such mineral salts 7 1.3 Leaf as an organ for when transferring the sections to photosynthesis avoid damaging them. 7. Using a mounted needle, carefully Structure of a leaf place a cover slip on the section. Activity 1.6 Make sure no air bubbles are Observing the transverse section trapped. of a leaf 8. Using tissue paper, wipe off Work in a group of four excess water from the slide before Materials observing it under the microscope. Pieces of carrot, scalpel or sharp First use low power then medium blade, microscope slides, microscope power. cover slip, compound microscope, 9. Try to identify the following some water, dropper, mounted layers of tissue: upper epidermis, needle, dish e.g. petri-dishes or palisade layer, spongy mesophyll, glass dishes, a fine brush, young leaf vascular bundles, lower epidermis from dicotyledon e.g. Bidens pilosa, and stomata. peas, beans and monocotyledon like 10. Use a sharp pencil to draw the maize or grass. outline of the layers of tissues Procedure you have seen under low power 1. Take a carrot, wet it then slice magnification. Label the layers. it vertically, halfway down the 11. Under the medium power, middle. examine and draw a cell from 2. Insert the leaf blade into the slit each of the following layers: made in the carrot. Make sure that upper epidermis, palisade layer, the midrib of the leaf is placed spongy mesophyll and lower vertically along the centre of the epidermis. carrot. Trim off any protruding Study questions part of the leaf. 3. Hold the carrot in one hand, and 1. Relate the shape of the cell in the cut several thin sections quickly leaves to their function. and smoothly with a scalpel using 2. What do you notice about the the other hand (see activity on how arrangement of the cells in the to make sections for observation layers? Are they closely packed under the microscope). or loosely packed? Why do you 4. Put the sections in some water in a think this is? petridish. 3. Explain the purpose of the thin 5. Take a slide and put a drop or two cuticle. of water on it using a dropper. 4. The upper leaf surface darker 6. Select the thinnest section, green than the lower surface. preferably one that is cut through What is the significance of this? the midrib, and place it into the 5. Where are stomata located in drop of water. Use a fine brush aquatic plants? Why? 9  oxide and also allow for maximum 9. Leaf cuticle secreted by epidermis sunlight to fall on it. prevents excessive loss of water 3. Leaf epidermis has stomata that by transpiration and also allows allows for passage of carbon (iv) light to pass through and reach oxide into a leaf for photosynthesis photosynthetic cells. and oxygen out of leaf. 4. Leaf has vascular bundles for My environment my life! transport of photosynthetic Do not uproot the whole plant products (phloem), water and when plucking leaves. mineral salts(xylem). 5. Leaf has large air spaces between spongy mesophyll cells to allow Check your progress 1.2 for gaseous exchange between 1. Indicate TRUE or FALSE mesophyll cells. (i) The two main roles of 6. Palisade cells have numerous stomata on a leaf are chloroplast and located next gaseous exchange and to upper epidermis to receive transpiration. maximum sunlight. (ii) Epidermal cells in a leaf are also referred to as mesophyll cell. (iii) Palisade cells have the highest number of chloroplast in a leaf. (iv) More light is trapped Chloroplasts by chloroplast in the Fig. 1.8: Palisade cells epidermal cells because they are in direct contact 7. Extensive network of veins in leaf with sunlight. conduct water and mineral salts to 2. Use diagram to differentiate photosynthetic cells or transport between guard cells and away photosynthetic products. surrounding epidermal cells. 3. Give biological explanation for the following: (i) Leaves are well adapted for effecient diffusion of carbon dioxide. Veins (ii) Existence of cuticle on the Fig. 1.9: Network of veins in a leaf leaf surface. (iii) Location of chloroplast on 8. Leaf mosaic pattern prevents lower the upper epidermis. leaves from overshadowing by upper leaves. 12 1.4 Factors affecting rate Procedure of photosynthesis 1. You are provided with the Some of the carbohydrates materials above. manufactured during photosynthesis 2. Come up with the steps showing are converted to other substances, such how light intensity affects the rate as proteins which are necessary for of photosynthesis. growth and development. This means 3. Follow the steps to carry out the that the rate at which photosynthesis experiment showing how light takes place influences the rate of intensity affects photosynthesis. growth and development in plants. Study questions The following factors influence photosynthesis: 1. Was the average number of bubbles Light intensity of gas per minute the same under Temperature different light conditions? Carbon dioxide concentration 2. Why was the average number Water of bubbles produced per minute If the level of one of the factors is reduced different? but the others remain the same, the rate 3. Explain the effect of light intensity of photosynthesis will reduce. on the rate of bubble formation. On the other hand, if the level of one of the factors increases, and the Were your steps the same as the ones others remain constant, the rate of shown below? photosynthesis will also increase up to a certain point beyond which it does not 1. Prepare two set-ups of apparatus increase any more. At this point other as shown below. factors limit the rate of photosynthesis. Test Oxygen Light intensity tube gas Test tube Activity 1.8 Potted plant What is the relation of light intensity to rate of photosynthesis? Water Beaker Beaker Work in group of six Materials 2. Place the set-up first inside the Water plants e.g. Elodea and laboratory, count the number of Spirogyra, beakers, glass funnels, bubbles released in a minute by sodium bicarbonate (to be dissolved the plant. Repeat this five times, in the water). and calculate the average number of bubbles released by the plant in a minute. Note this down. 13  Effects and symptoms of Potassium deficiency Plants lodge before maturing. Leaves of crops develop a burnt appearance on the tips and margins, i.e. they are scorched. Scorching starts with older leaves Fig. 1.15: Leaf affected by phosphorous die back occurs. deficiency Leaves curl. c) Potassium Upper leaf surface lose chlorophyll Debate!! and become yellow or chlorotic. Potassium plays a vital role in Premature leaf fall. plants. Stunted plant growth with stems having shorter internodes. The Role of Potassium: Fruit or seed is somewhat It is essential for nitrogen shrivelled wrinkled metabolism and protein synthesis. It increases plant vigour and Plants like beans, potatoes and disease resistance. The plant stalks sugar beet are prone to rust attack. are strengthened making them less prone to lodging and to bacterial/ fungal infections. It promotes root development. It helps in synthesis of sugars and starch and their translocation. It helps in plant metabolism. It is essential for chlorophyll formation. It regulates the availability and use Fig. 1.16: Leaf affected by potassium of nitrogen and phosphorus. It deficiency assists in the uptake of nitrates. d) Magnesium It increases the size of grains and Activity 1.13: seeds. It is necessary for the Imagine you are a radio presenter. neutralisation of organic acids in You are assigned to investigate on plants. the role of magnesium, calcium and It acts as an activator for different sulphur to a plant. This information enzymes. has to be accurate because it will be It enhances plant tolerance to used in helping farmers around by cold and other adverse weather Ministry of Agriculture. conditions. How will you go about it? It increases crop quality e.g. in cut flowers. 19 Effects and symptoms of boron deficiency Effects and symptoms of manganese Boron deficiency is indicated by a deficiency change in colour at the tips of growing Its deficiency results in chlorosis in shoots. The terminal bud becomes light young leaves. The loss of colour is often green with traces of reddish-brown. followed by the development of dead It may cause the shoot tip to die and tissue spots (necrosis) and dead spots flowering may fail to occur. may drop off giving the leaf a perforated appearance. 2. Copper It is an activator or catalyst for various 5. Molybdenum chemical reactions within the plant. It It is associated with nitrogen utilisation. promotes formation of Vitamin A. It It is required in very little amounts. also regulates the functions of nitrogen. Effects and symptoms of molybdenum Effects and symptoms of copper deficiency deficiency Its deficiency results in retarded plant Its deficiency results in foliage with a growth and yellowing of leaves. chlorotic condition showing bleached 6. Zinc appearance. Citrus fruits show die back It is associated with availability of iron of new shoots and the stem is marked and manganese which are essential in with a reddish brown secretion (gummy chlorophyll formation. exudates). Cereals show chlorotic leaf tips and failure to set seeds. Effects and symptoms of zinc deficiency 3. Iron Its deficiency results in reduced fruiting. Iron is essential for the formation of The plants terminal leaves may become chlorophyll. It is also necessary in abnormally small. the plant respiration and metabolism processes. Check your progress 1.3 Effects and symptoms of iron deficiency 1. Using a table, list all macro- nutrients and micro-nutrients Its deficiency causes leaf chlorosis i.e. and their deficiency symptoms. paleness at the leaf tips and margins 2. Which nutrients do these plants while the veins remain green. The lack? young leaves become affected first and may curve in an upward direction e.g. in cabbage. 4. Manganese It is associated with copper and zinc metabolism. It acts as a catalyst in plant growth processes. a) __________________ 22  4. Describe how a plant suffering from magnesium deficiency looks like. 5. How will you apply knowledge learnt in macronutrients and micronutrients in plants to animals. 6. Plants need enough a) __________________ micronutrients and 3. Your neighbour, Chol is doing macronutrients. Explain maize farming in large scale. She 7. Design a puzzle which includes suspects that the maize plants all micronutrients. are suffering from nitrogen deficiency. As a Biology student, how will you confirm whether what she is saying is true or false? 23  Canine Incisors (c) Premolars } Canine They are located after the canines, } Premolars towards the back of the jaw. They have } broad top surfaces usually with two Molars projections called cusps that give them Palate a ridged appearance. Fig 2.9 illustrates a premolar tooth. They are used to crush and grind food. Fig 2.6: Upper jaw showing human dentition Ridges (cusps) Crown (a) Incisors They are located at the front of the jaws. They are shaped like a wedge or chisel, see fig 2.7. This creates a flat surface Root with a sharp edge that makes incisor teeth suited for cutting and biting. Fig 2.9: A premolar Crown (d) Molars neck They occupy the back of the jaw, in the cheek. They too have broad top surfaces with four or five cusps, which form a Root ridged surface as shown in fig 2.10. They are also used to crush and grind food. Fig 2.7: An incisor (b) Canines Ridges (cusps) Crown They are located on the left and right of the incisors. Canines are pointed teeth as shown in fig 2.8. Their basic function is to pierce and hold food. In human Root beings, canines are poorly developed as they are not needed for holding onto prey. Fig 2.10: Molar tooth Crown Human beings have two sets of successive neck teeth. The first set is known as the milk set or deciduous teeth. They form in the jaw before birth. In a new-born baby, the Root teeth are not visible above the gum. They erupt out of the gum at about five months. At two years, the baby has all the teeth Fig 2.8: A canine 28  Forms the bulk of the tooth. Replaces worn out enamel. Check your progress 2.2 Prevents the teeth from cracking. 1. Match the tooth with its Pulp cavity function. It is found at the centre of the tooth. The pulp cavity contains numerous blood Tooth Function capillaries and sensory nerves. These (a) Crush and grind enter the pulp cavity through a small food opening at the bottom part of the root. The blood capillaries supply nutrients and oxygen to the cells of the pulp (b) Grinding food cavity. They also transport waste material and carbon dioxide from the tooth. The sensory nerve fibres have nerve endings that make the tooth sensitive to temperature and pain. Special cells in (c) Cutting and biting the pulp cavity produce dentine which food forms the bulk of the tooth. Cement It is similar to bone in structure. It lines (d) Piercing and the root and holds the tooth in its socket holding food in the jaw. Periodontal membrane 2. Explain how the arrangement of This membrane is found between the teeth in the mouth is related to cement and the jaw bone in the socket the function of the teeth. of the tooth. It contains cells that secrete 3. Why toothache if decay reaches cement. It also allows the tooth to dentine? move slightly to avoid breaking during 4. Why do tooth have hard chewing. enamel? Common dental diseases The mouth cavity is a habitat for bacteria and other micro-organisms. These 30 Health check! the necessary nutrients required for maintenance of strong and healthy It is advisable to clean teeth a teeth. Examples of food rich in minimum of two times a day. fibrous material are nuts, sugarcane, pear and raw carrots. Care of teeth (v) The teeth should not be used to Most dental diseases can be prevented remove bottle tops or crack nuts. with proper care of the teeth and gums. Such use of teeth could cause This would require a proper diet and cracks in them. Food particles and good oral hygiene and other measures. bacteria could occupy the cracks The following are some useful measures and cause dental cavities. in preventing dental diseases. (vi) Occasionally, when brushing is not possible, the mouth should be (i) A diet rich in calcium and vitamin rinsed thoroughly with water to D is important in the growth of remove food particles between the strong and healthy teeth. This is teeth. especially important in pregnant mothers, breast-feeding mothers (vii) Taking water with minute quantities and children. of fluoride and using toothpaste with small amounts of fluoride (ii) Brushing the teeth regularly, could prevent dental cavities. particularly after meals and Fluoride helps in the formation of before going to sleep to remove food particles and to reduce the hard, strong teeth. accumulation of plaque. Food (vii) Regular visits to a dentist will help particles that are stuck between in the detection of cavities and the teeth can also be removed by diseases of the gum at an early inserting a strong nylon thread stage. into the gaps between the teeth and pulling the thread upwards. Activity 2.4: Research Activity Thread used in this way is called Work in a group of four dental floss. 1. Devise an experiment to (iii) Avoiding sweet and sugary food in investigate the effects of order to prevent multiplication of hydrochloric acid, lemon juice bacteria on the teeth. and fizzy drinks on egg shells. (iv) Eating food that contains enough 2. Share your finding with the rest of fibrous material to stimulate blood the class. circulation in the teeth due to the chewing process. Efficient blood circulation supplies the teeth with 32  Check your progress 2.3 2. Wet the fur and then pinch up 1. The outer layer of the crown of the skin in the middle of the a tooth is resistant to attack by abdomen. bacteria. 3. Insert the point of your scissors, cut skin upwards along the (a) Name the outer layer. midline to the neck, downwards (b) State the minerals and near the reproductive opening the vitamins needed in and outwards along the four the diet for the healthy limbs. development of this layer. Safety warning: Be careful when using (c) Explain how bacteria can sharp objects like scissors and surgical gain entry through this pins to avoid cutting and pricking layer into the tooth and yourself. cause dental decay. 4. Separate the skin from the underlying muscle with your 2. How do the functions of teeth scalpel and pin it out on either contribute to the process of side of the body. cortex, medulla, digestion? pelvis, renal artery, renal vein and urethra. 2.3 The digestive system 5. Draw and label the structures you have identified. Activity 2.5: Dissection of a rabbit 6. Open up the abdominal cavity by to observe the digestive system holding your scissors horizontally and compare it to the human and carefully cutting through digestive system the muscle layers along the mid- Materials ventral line, forwards to the start Charts and models of the human of the breastbone and backwards digestive system to near the reproductive opening. Rabbit (preserved or just killed) 7. Cut across the body muscle Dissecting instruments immediately behind the ribs and Cotton towards the rear of the abdominal Dissecting board or tray cavity. Pins 8. Pin back the body flaps. Procedure 9. Locate the following organs: liver, stomach, small intestine (much 1. Place the rabbit on its back on the coiled), caecum colon or large dissection board and stretch out intestine, rectum, bladder (bag- the body by tying the limbs to the like). sides of the board with a pin. 10. Without disturbing the organs, Caution: Gloves must be worn while make a drawing of the abdominal performing dissection. This cavity. reduces the risk of infectious diseases 33 the digestive tract. The acid converts intestinal mucosa into the blood. The the inactive pepsinogen into the intestine ends via the large intestine in active proteolyticenzyme,pepsin, the vent or cloaca which serves as the which breaks down certain common exit for renal and intestinal specific peptide bonds found excrements as well as for the laying of in proteins, to produce a set eggs. However, unlike mammals, many of peptides, which are amino acid birds do not excrete the bulky portions chains that are shorter than the (roughage) of their undigested food original dietary protein. The gastric (e.g. feathers, fur, bone fragments, juices (hydrochloric acid and and seed husks) via the cloaca, but pepsinogen) are mixed with the regurgitate them as food pellets. stomach contents through the muscular contractions of the gizzard. The nutrientabsorption. Sphincters control gizzard is composed of four muscular the food and fluid movement between bands that rotate and crush food by three regions. The three regions shifting the food from one area to the include the foregut (stomatodeum) the next within the gizzard. The gizzard midgut (mesenteron) and the hindgut of some species of herbivorous birds, (proctodeum) contains small pieces of grit or stone In addition to the alimentary canal, called gastroliths that are swallowed by insects also have paired salivary the bird to aid in the grinding process, glands and salivary reservoirs. These serving the function of teeth. The use structures usually reside in the thorax of gizzard stones is a similarity found (adjacent to the fore-gut). The salivary between birds and dinosaurs, which glands produce saliva; the salivary ducts left gastroliths as trace fossils. lead from the glands to the reservoirs The partially digested and and then forward through the head to an pulverized gizzard contents opening called the salivarium behind are passed into the intestine, the hypopharynx; which movements where pancreatic and intestinal of the mouthparts help mix saliva enzymes complete the digestion of the with food in the buccal cavity. Saliva digestible food. The digestion products mixes with food, which travels through are then absorbed through the salivary tubes into the mouth, beginning the process of breaking it down. Beak Mouth Oesophagus Crop Glandular part of stomach Gizzard Intestines Cloaca Fig 2.14 Bird's digestion system 36  Check your progress 2.4 1. Compare digestive system in 4. What are some of the birds to that of human beings evolutionary advantages among 2. Draw and label insect digestive animals with a complete system. digestive tract? 3. What is the difference between a complete digestive system and an incomplete digestive system? How are these types of digestive systems related (or not) to extracellular digestion? 37  Lung capillaries than in the open circulatory system. { Pulmonary Mammalian circulatory system circulation Right { The mammalian circulatory system Left auricle auricle consists of a heart which keeps pumping Right Left in order to circulate blood through a ventricle ventricle { well-defined network of vessels around System circulation the body. There are three kinds of blood vessels; arteries, veins and capillaries. Structure and function of the heart, { System capillaries arteries, veins and capillaries Fig. 3.3 Closed circulatory system The open circulatory system works Structure of the heart best in organisms with a small body Activity 3.2 cavity e.g. insects. It is not efficient for large organisms such as vertebrates. To examine the structure of a Insects’ circulatory systems consist of a sheep/goat’s heart long tubular heart along the back side As a class (dorsal) of the organism. When the heart contracts, blood in it is forced out Materials at its front end. The blood then flows Sheep’s heart with all parts and vessels into the haemocoel or body space where intact, hollow tubing, flat wooden exchange of materials with the tissues board, forceps, sharp scapel. takes place. It then re-enters the heart Procedure through openings called ostia. 1. Your teacher will dissect the heart Dorsal Heart portion of a sheep.. aorta of dorsal aorta Dorsal diaphragm 2. Observe keenly as he or she is dissecting. Study questions Ventral 1. Why was he or she using a sharp diaphragm scapel? 2. On observation you realised that Fig. 3.4 Closed circulatory system in a the heart was covered with layers grasshopper of fat. Explain the main reason for Closed circulatory system is found in this. annelids and vertebrates like mammals. 3. Are you able to identify parts It has an advantage over the open of the heart? If yes, relate the circulatory system because the pressure of structure of each part to their blood in it is high.This means that blood function. circulates faster, and hence transports substances to and from the tissues faster 40 pumps blood into the pulmonary artery. heart and back is called the pulmonary Semi-lunar valves at the opening of this circulation. artery prevent back flow into the right The left atrium pumps blood into the left ventricle. At the same time the triscuspid ventricle via the bicuspid valve. The left valve prevents any back flow of blood into ventricle pumps blood to all parts of the the right atrium. Tendons (heart strings) body, except the lungs. This blood leaves hold the valves in a closed position the left ventricle through the aorta. Semi- preventing them from turning into the lunar valves that open into the aorta atrium. The pulmonary artery carries prevent back flow of blood. blood to the lungs. The left ventricle walls are much thicker In the lungs the blood picks up oxygen than the right ventricle walls in order and gives up carbon (IV) oxide. It is to develop a high enough pressure to now said to be oxygenated and is bright pump blood to all parts of the body. The red in colour. It goes to the left atrium circulation of the blood from the heart of the heart via the pulmonary vein. to the tissues and back is called systemic This portion of the circulatory system circulation. where blood flow to the lungs from the Ascending aorta (to head and arms) Superior venacava Right pulmonary Aorta artery Pulmonary artery Right pulmonary Pulmonary vein vein Left atrium Right atrium Right ventricle Coronary artery Inferior Left ventricle venacava Descending aorta (to lower body) Fig 3.6 External structure of the heart 43 vessels called arterioles. The arterioles branch further within the tissues into finer vessels called capillaries. Capillaries Capillaries are fine branching blood vessels that form a dense network between the arterioles and venules. Thin endothelium (one cell thick) Cell Small lumen Fig 3.9: Capillary Capillaries have the following properties. layer of muscle and elastic fibres and an They have thin walls to allow for inner layer of cells, the endothelium. rapid exchange of substances. Veins have pocket valves at intervals They form a dense network which in their walls which allow blood to creates a large surface area over flow only in one direction towards the which the exchange of substances heart. They carry deoxygenated blood takes place. except the pulmonary vein which carries Their walls are narrow to allow oxygenated blood. high pressure build-up within Thin wall them. This ensures faster movement of substances out of them. They have very thin walls made up of only one cell layer for faster exchange of materials. Lumen Capillaries join to form larger vessels known as venules. Venules link up to Fig 3.10: Vein form veins. Portal veins have capillaries at both Veins ends. They are unique veins that carry Veins carry blood under low pressure blood from one organ to another, for from the tissues towards the heart. They example, the hepatic portal vein which have thin walls which are composed of carries blood from the small intestine to a thin outer fibrous coat, a thin middle the liver. 47 micro-organisms. They are transported blood cells are also very many in number. in the plasma. There are about five million red blood cells in every cubic millimetre (mm3) of vi. Transportation of nutrients human blood. However, the number of Many of the products of digestion such red blood cells varies depending on any as glucose and amino acids are dissolved of the following factors: in the plasma before they are transported Altitude: the higher the altitude the from the small intestines to the liver more they will be. either for storage or for further transport to cells in body organs. The state of health of a person: People with severe anaemia or Red blood cells (Erythrocytes) malaria have much fewer red blood cells in their blood. Discussion corner Red blood cells are made in the red bone What are red blood cells? marrow of the bones of the sternum and Explain why the number of red ribs. They circulate for about 100–120 blood cells increases. days in the body before their components To what role do the special are destroyed in the liver and spleen. shape of red blood cells play in Iron from destroyed cells is reused in relation to their function? the body to make haemoglobin in new red blood cells. These are very tiny cells. They are disc Functions of the red blood cells shaped and biconcave and appear as The main function of the red blood cells discs which are thinner in the centre than is to transport oxygen from the lungs to around the edge. the body tissues. The haemoglobin found in these cells readily combines with oxygen when the blood passes through the lungs to form oxyhaemoglobin. When the blood reaches a region with low oxygen levels like in the tissues, the oxyhaemoglobin readily gives up the oxygen it was carrying. It then reverts Fig 3.11: Red blood cell back to haemoglobin. The cells take up the oxygen, while haemoglobin is free The small size of red blood cells increases to be used again to carry more oxygen. their surface area to volume ratio for the diffusion of oxygen. Their cytoplasm Haemoglobin + oxygen tissue contains a red iron-containing pigment oxyhaemoglobin called haemoglobin. Red blood cells The red blood cells also play an important have no nucleus. This creates space for role in the transport of carbon dioxide. more cytoplasm and therefore more Most of the carbon dioxide from the haemoglobin to be packed in them. Red tissues enters the red blood cells where 50 iii. Neutrophils Neutrophils are the most common type of white blood cell in the body. Neutrophils are medium-sized white blood cells with irregular nuclei and many granules. They kill germs by means of a process known Fig 3.16: Eosinophil as phagocytosis or “cell-eating. vi. Basophil Basophils are the least frequent type of white blood cell, with only 0-100 cells per mm3 of blood. Basophils have the ability to secrete anticoagulants and antibodies that have function Fig 3.14: Neutrophil against hypersensitivity reactions in the iv. Monocytes bloodstream. Monocytes are the largest of the types of white blood cells. They have few granules in the cytoplasm when seen under the microscope. Monocytes turn into macrophages when they exit the bloodstream. As macrophages, monocytes do the job of phagocytosis (cell-eating) of any type Fig 3.17: Basophil of dead cell in the body, whether it is a Platelets somatic cell or a dead neutrophil. Blood platelets are also known as thrombocytes. They are fragments from larger cells. They are very small and have no nucleus. Fig 3.15: Monocyte v. Eosinophils There aren’t that many eosinophils in the bloodstream—only about 40-400 cells per mm3 of blood. They have large Fig 3.18: Platelets granules that help in cellular functions. Platelets are formed by the pinching off of Eosinophils are especially important bits of cytoplasm from large cells inside when it comes to allergies and worm the bone marrow. infestations. High eosinophil counts are associated with allergic reactions. 52 Although these bits of cytoplasm contain no nuclei, they are surrounded by a 6. A student in Magwi Secondary membrane. About 300,000 platelets are School took a blood smear from found in 1 cm3 of blood. They live for the fingertip and examined it about seven days. Platelets are involved under a microscope. in blood clotting when an injury occurs (a) Which was the most on the skin. abundant cell type that he observed ? describe one cell Check your progress 3.2 and state its function. 1. Which of the following (b) A number of cells that he statements is true concerning observed a large nucleus human blood? lobed and their outline A. Blood is not a tissue. looked like that of the B. The blood of all normal amoeba. What name did he human beings contains red give such cells? and white cells, platelets (c) Whats the function of the and plasma. cells that he observed in (b) C. Some people lack the above? ability to produce plasma. 7. What can one attribute the main D. Proteins are not normal causes of the circulatory system components of blood. to man? 2. Write true or false for the 8. A footballer fell down during following statements. a match and bruised his knee. A. Mature red blood cells lack Drops of blood were seen to nuclei. flow through the bruise for 20 B. Red blood cells contain minutes and then were seen to hemoglobin. stop. Describe the processes C. Deoxyhemoglobin carries which brought about the oxygen. cessation of blood flow at the D. Red blood cells lack injury. mitochondria. 9. How does the structure of 3. The ________ produces arteries and veins relate to their red blood cells which functions? transports____ and _____. 10. How do the heart and lungs 4. Of what advantage is it, for a red work together to pick up and blood cell to: deliver oxygen to the cells. (i) have a biconcave disc 11. Blood samples were taken shape? from groups of people living (ii) have haemoglobin? in different altitudes and the (iii) Lack a nucleus? number of red blood cells in 5. What is the main function of each mm3 of blood determined. white blood cells? The results of the survey are shown in the following table: 53  Lymph capillary Cervical lymph Jugular Tissue nodes vein cells Arteriole Subclavian vein Venule Mesentric Axillary lymph Tissue fluid Lymphatic lymph nodes vessel Gut Fig 3.19: Lymphatic capillaries Thoracic duct An antibody is a protein produced in the Inguinal blood that fights diseases. Just like blood lymph (groin) circulatory system which transports blood, lymphatic system transports Fig 3.20: Lymphatic system lymph. The lymphatic system is a network of tubes throughout the body that drains Lymphatic vessels fluid (called lymph) from tissues and Lymphatic vessels, unlike blood vessels, empties it back into the bloodstream. only carry fluid away from the tissues. Lymph is filtered through the spleen, The smallest lymphatic vessels are the thymus and lymph nodes before being lymph capillaries, which begin in the emptied into the blood. Blood vessels tissue spaces. Lymph capillaries are found tend to seep fluid into surrounding tissue. in all regions of the body except the bone The lymphatic system drains off any extra marrow, central nervous system and fluid to stop the tissues from puffing up. tissues, such as the epidermis, that lack The lymphatic system consists of a fluid blood vessels. (lymph), vessels that transport the lymph Lymphatic organs and organs that contain lymphoid tissue. Lymphatic organs are characterised by Lymph clusters of lymphocytes and other cells Lymph is a fluid similar in composition in branching connective tissue fibres. The to blood plasma. It is derived from blood lymphatic organs include: plasma as fluids pass through capillary Lymph nodes walls at the arterial end. As the interstitial Tonsils fluid begins to accumulate, it is picked up Spleen and removed by tiny lymphatic vessels Thymus and returned to the blood. Lymph nodes Lymph nodes are small bean-shaped structures found in particular locations in the body. Such places include neck, 55 armpits and between the lungs. Lymph Check your progress 3.3 nodes contain white blood cells which fight infections. 1. The spleen is a lymph organ that filters blood and also acts as a Tonsils reservoir for_________. Tonsils are the two lymph nodes located 2. Both lymph and venous blood on each side of the back of the throat. flow are heavily dependent on They help to prevent the body from A. the pumping action of the infection. heart B. Skeletal muscle The spleen contractions and The spleen is located in the upper left differences in thoracic abdominal cavity, just beneath the pressures due to diaphragm, and posterior to the stomach. respiratory movement It is similar to a lymph node in shape and C. Contraction of the vessels structure but it is much larger. The spleen themselves is the largest lymphatic organ in the body. D. Two-way valves The thymus 3. Draw and label the lymphatic system. The thymus is a soft organ with two lobes that is located inside the ribcage, just behind the breastbone. It is relatively Immune response large in infants and children but after Viruses, bacteria and other micro- puberty it begins to decrease in size so organisms that cause diseases are called that in older adults it is quite small. pathogens. They are found everywhere around us: in water, in soil, in the food we Functions of the lymphatic eat, the air we breathe, on our bodies, and system even inside the body. When pathogens The lymphatic system has multiple enter the body, they reproduce in large interrelated functions: numbers and produce toxins or poisons that affect the normal cell functions. This i. It is responsible for the removal of makes us ill. interstitial fluid from tissues. The skin, mucus, stomach acid, etc ii. It transports white blood cells to prevent most pathogens from getting to and from the lymph nodes into the our cells. But this is not enough. bones. Pathogens still enter our bodies. The iii. It absorbs and transports fatty body has the ability to distinguish acids and fats as chyle from the between substances that are part of itself digestive system, and those that are foreign. This is because iv. It transports dendritic cells, to the different organisms have different types lymph nodes where an immune of proteins within them. When the response is stimulated. body recognises foreign protein in molecules or organisms that enter it, 56 it produces antibodies or special cells pathogen. Once the organism recovers that destroy or inactivate the foreign from the disease, material or organism. The production it can produce antibodies very quickly of antibodies and special cells that should the pathogen invade it again. inactivate a foreign substance is called the This makes the organism immune in immune response. This prevents disease, the sense that it cannot fall sick due to or in case of disease, it helps in healing. invasion by the same pathogen. Since The ability of the body to fight infection this happened naturally it is also known by producing antibodies or cells that as active natural immunity. destroy pathogens is called immunity. Active immunity can also be induced by Various tissues in our lymphatic system introducing antigens into the body of an make up the immune system. The organism through the use of a vaccine. immune system includes all the parts of A vaccine contains antigens composed the body that are involved in the of living, dead, or weakened pathogens. recognition and destruction of foreign They are used to stimulate the body to substances. It is made up of the following: recognise certain disease antigens and Bone marrow which produces white to respond to them. They usually do not blood cells White blood cells especially cause the disease. This is active artificial phagocytes and lymphocytes. Various immunity. tissues of the lymphatic system such as Passive immunity lymph nodes tonsils, thymus and spleen which accommodate lymphocytes. This is immunity that comes from using antibodies produced in one organism to Natural and artificial immunity protect another organism from a specific Immunity may be active or passive disease. These antibodies are usually extracted from the serum of an animal In active immunity the body that has recovered produces its own antibodies or natural killer cells (killer T cells) to from the disease. Such immunity does attack a particular antigen. not last long. Serum refers to plasma without the soluble protein In passive immunity a person fibrinogen. Passive immunity is also receives antibodies from another found in newborn babies when they get individual or animal. It is like donated immunity. the antibodies through breast milk or across the placenta in the uterus Active immunity before they are born. Such immunity It may develop as a result of having had gives protection to newborn a disease. The organism makes its own babies for a few months until their own antibodies as a result of contact with natural body defense system begins to the antigen from the disease-causing function. 57 Importance of vaccination against Check your progress 3.5 disease We have seen that vaccines are antigens 1. Fill the passage below that are artificially introduced into ______________is a type of the body of an organism to start an immunity that is found in immune response. This gives protection foetus and young children. The to the organism against certain diseases, ___________ of the mother sometimes for life. The antigens are crosses though the________ introduced into the body by injection into the foetus. Babies get the or orally by mouth in a process antibodies from the mothers called immunisation or vaccination. milk through _____________. This immunity lasts for a few In children, some diseases are life months after birth. The mothers threatening and the Ministry of Health ____________ protect the has prepared a proper programme of baby from infections before it immunisation to protect them from is able to manufacture its own such diseases. It is necessary that all antibodies. children are vaccinated against polio, diphtheria, tetanus, whooping cough 2. Passive immunity is not and tuberculosis. You must have been important to human body. Discuss. vaccinated as a child. Here is a quick way of finding out. Look for the scar on the outer part of your left arm. Gaseous exchange in protozoa See if your neighbour has a similar Protozoa one. This scar comes from immunising Protozoa are single celled organisms. children with BCG vaccine. Are your Examples of protozoa include Amoeba, younger brothers and sisters vaccinated? Plasmodium and Trypanosoma. What about other children in your locality? Find out and mention the These are microscopic organisms. They importance of vaccination to parents are mainly found in water or in the body whose children you suspect are not fluids of other organisms. vaccinated. Sometimes, people who go to The respiratory surface of protozoa is a foreign country are immunised against the cell membrane. Gaseous exchange yellow fever. In the case of an outbreak occurs across the cell membrane directly of a disease e.g. cholera or typhoid, mass by diffusion. Due to respiration, the vaccinations are carried out to prevent concentration of carbon (IV) oxide many deaths from taking place. inside the uni-cellular organism is higher than that in the surrounding water. Therefore, carbon (IV) oxide diffuses out of the organism into the surrounding 58 Comparison of aerobic and aerobic Check your progress 3.6 respiration Aerobic Anaerobic 1. When lactic acid builds up in respiration respiration the blood, a person is said to be Requires oxygen to Does not need in oxygen debt. This debt must take place. oxygen in order to eventually be paid. Suggest how take place. the debt is paid. There is complete There is incomplete 2. Give the difference between breakdown of glucose breakdown of molecule. glucose; leading aerobic and anaerobic to the formation respiration. of intermediate compounds. Large amount of Much less energy energy released from released from each each molecule of molecule of glucose. glucose. The by-products The by-products formed are carbon formed are carbon dioxide and water. dioxide and ethanol in plants and lactic acid in animals. Occurs in the Occurs only in the cytoplasm and in the cell cytoplasm. mitochondrion. 60 (c) Nitrogenous wastes Nitrogenous wastes including urea, some organs such as old leaves which urine, ammonia and uric acid are are shed off. produced from breakdown of excess Plants recycle some of their waste amino acids. The process by which products therefore counter the excess amino acids are broken down problem of accumulating them. is called deamination. Ammonia is a Carbon dioxide from respiration highly toxic compound that requires is used in photosynthesis while a lot of water to excrete. Therefore, ammonia from metabolism of amino only fresh water organisms are able acids is re-used to synthesize more to excrete it. In other organisms such amino acids. as mammals, marine fish and adult amphibians; ammonia is reacted with Check your progress 4.1 carbon dioxide and converted to urea. 1. Nitrogenous wastes are products Urea is less toxic and requires less water of breakdown of to excrete and is therefore the main A. Lipids nitrogenous waste substance excreted B. Mineral salts in mammals. Uric acid is insoluble and C. Proteins requires very little water to excrete. It is D. carbohydrates the main nitrogenous waste substance 2. W h i c h o f t h e f o l l o w i n g excreted by birds, insects and reptiles. nitrogenous waste products is Other waste products most toxic? A. Uric acid Bile pigments are produced from break- B. Ammonia down of haemoglobin of dead red blood C. Urea cells. Mineral salts such as sodium chlo- 3. Carbon dioxide is produced by the ride accumulate during metabolism. If process of these waste products accumulate to high A. Gas exchange levels, they could be toxic to the organ- B. Photosynthesis ism’s body and cause cell death. Other C. Respiration than the metabolic wastes, excess water D. Deamination and mineral salts are also removed from 4. Fill the blank spaces in the bodies of higher organisms like human paragraph that follows with beings. Used hormones and drugs are suitable terms. also excreted from the human body. Excretion involves the removal Excretion of metabolic waste products of ………………………. waste in plants is not a problem since: products from the body. The liver Plants manufacture the organic carries out ……………………… materials they require depending resulting to the formation of on the need, hence waste products nitrogenous wastes including do not accumulate to toxic levels. ……………………. , urea and Plants accumulate waste products in ……………………… Fresh water 63  Gastric Stomach possess the following adaptive features: Crop caeca Intestine Have numerous gill filaments to increase surface area for Oesophagus diffusion of carbon dioxide. Mouth Anus The gill filaments are covered Rectum with moisture and mucus which dissolve carbon dioxide Malphigian tubules hence it diffuses faster in Fig 4.3: Excretory system in a grasshopper solution form. The respiratory surfaces of insects that The gill filaments also have dense remove carbon dioxide as a metabolic capillary network to supply blood waste are adapted by having: to the gills hence maintaining a The tracheoles have tracheole fluid steep diffusion gradient between to dissolve carbon dioxide which the blood and water therefore diffuses rapidly in solution form. ensuring rapid diffusion of carbon Highly branched tracheal system dioxide out of the blood. to increase surface area over which The gill filaments are also thin to the respiratory gas diffuses out of reduce distance of diffusion of the body. carbon dioxide. Excretion in higher animals a) Excretion in fish Gill bar Fish utilize kidneys primarily for removal Gill of nitrogenous waste products but also rakers use the gills to get rid of ammonia. The digestive tract and the skin are also used to get rid of metabolic wastes. The waste products include nitrogenous waste, excess water and mineral salts. Type of Gill filaments the major nitrogenous waste product Fig 4.4 Structure of gills eliminated will however depend on the environment where the fish lives. b) Excretion in birds and Fresh water bony fish like Tilapia reptiles excrete ammonia since they have These organisms use the kidneys to abundant water to remove the highly get rid of nitrogenous wastes which toxic compound. are extracted from the blood and then Marine fish excrete a non-toxic excrete it as uric acid through the compound called trimethylamine oxide ureters. The uric acid is then shed into which requires little water to excrete. the intestines and deposited with the Fish excrete carbon dioxide through faecal matter. the gills. The gill as a respiratory surface 66 c) Excretion in amphibians Fat bodies Amphibians excrete nitrogenous wastes Renal artery Kidney in the form of ammonia, uric acid Posterior and urea. They have kidneys which vena cava remove nitrogenous wastes from blood, Adrenal gland combine it with water to form urine that Renal portal is channeled out of the body through vein Rectum Renal vein the cloaca when the bladder if full. Dorsal Aorta Apart from the lungs, amphibians like Urinary OPening of tract urethra frogs use their skin remove carbon Cloaca dioxide. Cloacal aperture Opening of The skin as a respiratory surface is: urinary bladder Fig 4.5: Excretory system in amphibians Thin to reduce distance of diffusion and enable efficient d) Excretion in human beings removal of carbon dioxide. The main excretory organs in humans Moist to dissolve respiratory gases include: lungs, kidneys, skin and liver. which diffuse faster in solution Refer to table 4.1. The skin excretes form. excess water, mineral salts and traces Highly vascularised to ensure of urea through sweat while the lungs efficient diffusion of carbon remove carbon dioxide. The liver plays dioxide out of the lungs. an important role of deaminating excess Mammals, fish, reptiles and amphibians amino acids to form urea. The amine part of the amino acid is removed as use the lungs to remove carbon dioxide; ammonia while the carbon skeleton a product of cellular respiration. The is converted to glycogen and stored in lungs are adapted for this function in the liver or muscles for later use. Since the following ways: ammonia is highly toxic, it is reacted Numerous alveoli (the site of with carbon dioxide to form urea which gaseous exchange in the lungs) to is shed into the blood and transported increase surface area over which to the kidney for excretion. The kidneys carbon dioxide diffuses. remove the nitrogenous wastes from Thin epithelial lining of the alveoli blood. to reduce distance of diffusion The urinary system hence rapid diffusion of carbon The urinary system is a group of organs dioxide. that remove urine from the body. It Moisture lining on the alveoli to consists of the kidneys, ureters, urinary dissolve carbon dioxide to enable bladder and associated blood vessels. faster diffusion in solution form. The kidneys are dark red bean-shaped Dense capillary network to ensure structures located at the back of the maximum diffusion of carbon abdominal cavity. They are supplied dioxide from blood. with oxygenated blood that carries nitrogenous waste by the renal artery. 67  Distal convoluted tubule Glomerulus Bowman's Afferent arteriole capsule Capillaries Efferent arteriole Renal artery Proximal convoluted Renal vein tubule Collecting duct Loop of Henle Fig 4.8: Structure of nephron Structure and function of the nephron Filtration of blood and urine formation a) Filtration occurs in the nephron. Each nephron Blood flowing through the glomerulus is under high pressure. In addition consists of a single glomerulus, renal to this, the efferent arteriole leaving capsule, renal tubule and blood the glomerulus is narrower than the capillaries. Afferent arteriole brings in afferent arteriole creating more pressure oxygenated blood into the nephron. It build up at the glomerulus. As a result then branches into smaller capillaries of the high pressure, fluid part of blood called glomerulus. The capillaries containing small sized molecules such coalase to form efferent arteriole that as water, mineral ions, urea, glucose takes blood away from the glomerulus. and amino acids filter through the small The efferent arteriole then branches pores of the capillaries and enter into the renal capsule (Bowman’s capsule). This into capillaries that transverse the renal is termed as ultrafiltration. Molecules tubules before rejoin to form the renal of large size like blood cells and plasma vein that takes deoxygenated blood proteins do not filter through the small away from the kidneys. glomerular pores. About 180 liters of The process of urine formation occurs in filtrate are by the kidneys during a 24 two main stages: filtration and selective -hour period. reabsorption. 69 b) Selective reabsorption Have villi and microvilli that The filtrate in the renal capsule referred further increase surface area for to as glomerular filtrate flows to the reabsorption. proximal convoluted tubule where: Thin walled to reduce distance of All amino acids and glucose are diffusion and ensure maximum reabsorbed back into the blood reabsorption of solutes and stream in a normal human. water molecules back into the bloodstream. Some water and mineral salts are The filtrate then flows to the loop also reabsorbed. of Henle where most of the water This is called selective reabsorption. molecules are reabsorbed back into Amino acids, glucose and mineral salts the bloodstream. The loop of Henle is are taken up by active transport while located in the medulla of the kidneys. water is reabsorbed passively by osmosis. Mineral salts are actively removed from The proximal convoluted tubule is the filtrate into the medullary tissues; adapted for selective reabsorption in the resulting to high osmotic pressure following ways: in these tissues. Water molecules are It is highly coiled to slow down therefore reabsorbed via osmosis from rate of flow of filtrate to allow more the ascending loop of Henle into the time for more reabsorption. blood stream as the filtrate flows to the It is also long to increase surface distal convoluted tubule. area for reabsorption of substances At the distal convoluted tubule, The epithelial cells have dense reabsorption of mineral salts including mitochondria to provide ATP sodium and chloride ions occur. Apart energy for the active uptake of from reabsorption, tubular secretion of solutes back into the bloodstream. ions also occur. Table 4.1 Summary of excretory products in % Substance Plasma % Glomerular filtrate Urine % % Water 91-93 91-93 95 Uric acid 0.003 0.03 2 Glucose 0.1 0.003 0.05 Protein 8.0 0.1 - Amino acids 0.05 - - Sodium 0.3 0.05 - Chloride 0.37 0.3 0.5 70 Reabsorption of sodium ions occurs under the influence of aldosterone Check your progress 4.3 hormone secreted by the adrenal glands 1. Which structure do insects use located above each kidney. Aldosterone for excretion hormone is secreted when a drop in A. Nephridian pore blood pressure is detected; resulting to B. Flame cells reabsorption of sodium ions back into C. Malpighian tubules the blood stream. Tubular secretion D. Coelom that occurs at the distal convoluted 2. Marine fish excrete tubule involves pH regulation. The pH A. Urea of plasma is maintained within a narrow B. Ammonia range of 7.2-7.4. If the pH drops below C. Uric acid 7.2, hydrogen ions (H+) are actively D. Trimethylamine oxide secreted from the blood into the lumen of distal convoluted tubule resulting to 3. Organisms that face water an increase in pH of plasma. On the shortage excrete uric acid other hand, if the pH rises above 7.4, because hydrogen carbonate ions (HCO3-) are A. It is small in amount actively secreted from blood into the B. It insoluble and requires lumen of the distal convoluted tubule; less water to excrete resulting to a drop in pH of plasma. C. It dissolves to form harmless compounds The filtrate then flows to the collecting D. It passively diffuses out of duct where reabsorption of water occurs the body depending on the dehydration state of the body. If the osmotic pressure of blood 4. What is the functional unit of is high, the hypothalamus stimulates the kidney? the pituitary gland in the brain to A. Glomerulus secrete Antidiuretic hormone (ADH) B. Kidney tubules also called vasopressin which diffuses C. Nephron into the blood to the kidneys. ADH D. Cortex causes the kidney tubules, especially the 5. The kidneys play an important collecting duct to be more permeable role in homeostasis because to water. Hence, water molecules are A. Breakdown toxic metabolic reabsorbed before the filtrate flows as wastes in the body urine to the pelvis. Several nephrons B. Remove carbon dioxide empty their urine into a common from the body collecting duct. The composition of the C. Regulate the concentration filtrate varies greatly as the filtrate flows of various substances in from the proximal convoluted tubule to the body the collecting duct. D. Control glucose level in the body 71  6. In the kidneys, filtration of With a friend, think about how blood occurs in the temperature is regulated in a home. A. Medulla Compare that to what happens in B. Cortex the body. Which other things require C. Ureter regulation in our bodies? D. Loop of Henle 7. During filtration, small substances are filtered into Activity 4.6 the …………………… the filtrate that flows to the Work in groups proximal convoluted tubule Requirements is called …………………….. 4 basins with warm water, 4 basins All …………………….. with ice cold water, thermometer and and ………………………. stopwatch. Are reabsorbed back into the blood stream through Procedure …………………………. 1. Prepare a table as shown in table The proximal convoluted 4.3. tubule has abundant 2. Record initial body temperature ……………………………….. of four of the group members in to supply energy for the the table. Two members of the selective reabsorption of these group will do the measuring and substances. Most water is recording of body temperature of reabsorbed at the the group participants. 3. Let the four students immerse 4.4 Homeostasis their feet in ice cold water for Discussion corner twenty seconds and record their body temperature. Study the diagram below on 4. Let the four students then temperature control. The illustrations in A shows what happens in a home immerse their feet in very warm scenario. The illustrations in B shows water for twenty seconds and what