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. Significant cooling would be required to reverse melting of glaciers and the Greenland ice sheet, which formed during past cold climates. The present CO2-induced warming of the Earth is, therefore, fundamentally irreversible on human lifespan. The quantity and rate of further warming will depend almost entirely on how much more CO2 people emit. Ozone layer and human activities How do human activities affect the ozone layer? Group Activity 3.10 In your groups describe the graph below. What do you see? What does that mean? Suggest the human activities that contribute to the variations in the graph. Fig. 3.20: Ozone layer depletion graph. The facts The Earth’s atmosphere has three main problems: ozone layer depletion, acid rain formation and greenhouse effect. Ozone layer is a layer in the Earth’s atmosphere containing a high concentration of trioxide (O3). There are two types of ozone layers: high-level ozone (stratosphere ozone or protective ozone) and low-level ozone (ground level or troposphere ozone or harmful ozone). Fig. 3.21: Earth’s atmosphere. Over Antarctica, there have been found (in 1985) holes in the high-level ozone layer that are thought to be caused by the action of chlorine from CFCs. Chlorine + Ozone Chlorite + Oxygen The high-level ozone depletion increases with each chlorite released. Reduction of high-level ozone exposes biodiversity to harmful ultraviolet radiation from the sun. This increases the risk of skin cancer, cataracts, mutations, as well as sunburns. Ozone depletion preventive measures To reduce destruction of the highlevel ozone layer, reduce or eliminate the production and use of CFCs by developing alternatives, because CFCs have low-biodegradability. Individual efforts include avoiding using products containing chlorofluorocarbons; do not buy chlorofluorocarbon products. National efforts include government of South Sudan should ban chlorofluorocarbons. The government of South Sudan should encourage the use of chlorofluorocarbons free products. Government should also sign international agreements on reducing ozone depletion. Global efforts include the Montreal Protocol signed as an international agreement by many countries in 1987. The treaty aims to reduce the use of chlorofluorocarbons and stop using it completely by 2000. USA and 12 countries in Europe agreed to stop using chlorofluorocarbons in 2000. 83 • • Increase vehicle fuel efficiency and support other solutions that reduce
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South Sudan fossil fuel use. Place limits on the amount of carbon that polluters are allowed to emit. • Build a clean energy economy by investing in efficient energy technologies, industries, and approaches. • Reduce tropical deforestation while increasing tree planting. • Move near your workplace or work from home to reduced reliance on cars. Investing in new infrastructure. Bad roads can lower the fuel economy of even the most efficient vehicle. • • • Build more efficient buildings requiring less air conditioning. Improved power plant efficiency and transmission of power to end users. Substituting natural gas for coal to reduce black carbon emission. Promote the use of nuclear energy to generate electricity. • • • Development in the use of wind power. • Use of solar photovoltaic power. • Use of biofuels. • Agricultural soils management. Check your progress 3e Suggest ways of deaking with environmental pollution and climate chage in your locality. Did you know? If your shadow is taller than you are (in the early morning and late afternoon), you are probably getting less UV exposure. If your shadow is shorter than you are (around midday), you are getting higher levels of UV radiation. Seek shade and protect your skin and eyes. Global warming control How could global warming be controlled? Group Activity 3.11 “Healing the planet starts in your car garage, in your kitchen and at your dining room table.” Write an essay to explain these words. Present your essay before the class. This link might help you: http://globalwarming-facts. info/50-tips/2/ The facts • Global warming is primary because of greenhouse gases, therefore, reduce burning of fossil fuels and natural gas and instead use renewable energy sources. • Also, reduce of cutting of trees for agricultural activities such as keeping ruminants and growing paddy rice. • Expand the use of renewable energy and transform our energy system to one that is cleaner and less dependent on coal and other fossil fuels. 84 Unit 4 Respiratory system and exchange with the environment Learning outcomes Skills Attitudes • Investigate the process of aerobic and anaerobic process of respiration and the effect of temperature. • Observe and compare the • Appreciate the role of respiration in living organisms. • Appreciate structures of respiratory systems of humans, frogs, fish, among others. how organisms produce energy Knowledge and understanding • Explain the structure and function of the respiratory systems in animals and its role in exchange between organisms and the environment. 4.1 Respiration Group Activity 4
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.1 Given that composition of inhaled and exhaled air as tabulated in Table 4.1 below, design a bar chart to compare the inhaled and exhaled air. Table 4.1 Composition of inhaled and exhaled air Substance Nitrogen Oxygen Carbon (IV) oxide Inhaled air (%) Exhaled air (%) 78 21 0.39 78 16 4 (a) What do you observe from the bar chart? (b) Describe what that observation means? (c) How would you demonstrate that what your bar chart shows is true? The facts In Biology, the term “respiration” may mean one of two biological processes, therefore we will consider both, namely the internal or cellular respiration and external respiration involving gaseous exchange. 85 Types of respiration Internal or cellular respiration is the chemical process of releasing energy in the cell occurring in the presence of oxygen (aerobic respiration) or in the absence of oxygen (anaerobic respiration). External respiration or gaseous exchange or breathing is the process of transferring oxygen and carbon (IV) oxide across the respiratory surface to and from blood respectively. Practical Activity 4.1 You should have prerequisite knowledge from Chemistry on acidic/alkaline reactions, reaction of carbon (IV) oxide in water, pH levels and acidic/alkaline reactions with phenolphthalein solution. Requirements per group of five learners • 5 big balloons • 2 conical flasks of 250 ml • 2 straws • 1 bicycle pump • 10% KOH (potassium hydroxide) in a test tube • 2 droppers • Phenolphthalein indicator in a test tube Colourless pH 0-8.2 A B Fig. 4.1: Phenolphthalein in lower and higher pH conditions. 86 Procedure 1. Take two conical flasks and put 200 millilitres of water into both. 2. Add 20 drops of 10% KOH to both conical flasks using a dropper. 3. Add 20 drops of phenolphthalein solution and stir it with a straw. 4. Label the beakers as A and B. What are you trying to investigate with this experiment? 5. Each of you, blow air through your mouth into the balloons until they are full. 6. Fix the mouth of the balloon to one end of a straw while the other end is in conical flask A. 7. Release the air into the straw. Repeat this process for every member of the
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group. 8. Write down what you observe. Explain the reason for your observation. 9. Using the bicycle pump, pump fresh air into conical flask B. 10. Write down what you observe. • Explain the reason for your observation. • Compile a group report and present it to the rest of the class highlighting: – What you have learned from this experiment. – The precautions you took into considerations during the experiment. • The assumptions that you made in the experiment. • Compare your findings in this experiment with your observations in Group Activity 4.1. The facts Respiratory systems in animals 1. Investigate the structure of respiratory systems in animals such as fish, frogs, insects and mammals, with an emphasis on human respiratory structures. 2. Understand the role of respiration as gaseous exchange with the environment. Gas exchange surfaces or respiratory surfaces The most important component of respiratory system in animals is the respiratory surfaces because it is a transfer point of oxygen and carbon (IV) oxide between the environment and the cells. Examples of respiratory surfaces: • • • • In fish, they are gill filaments. In frogs, they are the skin, mouth lining and lung alveoli in adult frogs and gills in tadpoles. In insects, they are the tracheoles. In human beings, they are the lung alveolis. Work to do Explain the adaptations of the gill to its function. Spiracle valve Trachea Spiral of chitin supporting trachea Thin-walled air sac Muscle Cuticle mainly composed of chitin Thin-walled tracheole End of tracheole which can be fluid- filled Fig. 4.2: Tracheole of insects. 87 Fig. 4.3: Gill filaments of fish. Flow of freshly oxygenated blood back to the heart. Pulmonary venule I n i n h fl a t e ale d air s alv e o l u s Pulmonary arteriole Flow of oxygendepleted blood that has returned to the heart. A capillary network covers the surface of the alveolus to facilitate oxygen and carbon dioxide exchange. Fig. 4.4: Alveolus of human beings. 88 Fig. 4.5: Tadpole showing external gills. The facts Practical Activity 4.2 Requirements • A grasshopper • Specimen bottle • A hand lens Procedure Characteristics of respiratory surfaces 1. Catch a grasshopper from the • Provide a large surface area for gase
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ous exchange. • Moist and permeable surfaces. • Highly ventilated. • Highly vascularised. • One cell thick squamous epithelium. • Close association with respiratory pigment. field. 2. Put it in a specimen bottle. 3. Using a hand lens, observe how it is breathing in and out. 4. Release the grasshopper back to its environment. Gaseous exchange system of insects and its functions When the spiracle valves open, air containing oxygen is drawn into the tracheal system due to low pressure created as a result of relaxation of the abdominal muscles resulting in an increase in abdominal volume. Head Thorax Abdomen Wings Antenna Legs Cephalls air sacs Thoracic airsacs Thoracic spiracles 1st abdominal spiracle Abdominal air sacs Dorsal tracheal trunk Fig. 4.6: Inhalation and exhalation in insects. Lateral tracheal trunk Ventral tracheal trunk 89 When the spiracle valves close, oxygen is forced along the tracheal system due to contraction of abdominal muscles and into the air sacs and into the tracheoles. Gaseous exchange takes place in the tiny tracheoles which are in direct contact with tissue fluid. Oxygen diffuses into the tissue fluid through a concentration gradient, while carbon (IV) oxide diffuses into the tracheoles where it is in lower concentration, then diffuses to the tracheae and is expelled through the spiracles as a result of movement of abdominal muscles. If the tracheoles are supplying a muscle, the fluid located inside tracheoles at rest is withdrawn into the surrounding tissues when the muscle is active. This occurs when the muscle respire anaerobically producing lactic acid which increases the osmotic pressure of the tissue fluid in the muscle, so water is drawn out of the tracheoles by osmosis. This increases the rate of diffusion of oxygen into the muscle cell. Adaptations of the tracheal system to its functions include spiracle valves can open and close to prevent water loss if air is dry. Spiracles have hairs or spines in the opening of the tracheae just inside the spiracle, to trap dust ensuring clean air gets inside the tracheal system. The tracheal walls are spirally thickened with chitin which supports the tracheae keeping them open and allowing faster air diffusion, if the air pressure inside is reduced. Fig. 4.7: Trache
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ole of when the insect is active and when resting. The tracheal system is extensive spreading to every tissue, close to each cell. This reduces the distance the air has to diffuse to get to respiring cells. Tracheoles penetrate into every tissue up to the cell membrane, reducing the distance of diffusion. Tracheoles are very small and numerous increasing the gaseous exchange surface area. Tracheoles, internal surfaces are moist to dissolve oxygen before diffusion into the cell occurs. Tracheoles, walls are thin reducing the distance of diffusion and increasing the rate of diffusion. The removal of the fluid from the end of the tracheoles speeds up the rate at which oxygen can diffuse along it. 90 The facts Gaseous exchange system of a frog and its functions Practical Activity 4.3 Requirements • A frog • A hand lens • Specimen bottle Procedure 1. With the help of your group members, catch a frog and put it in a specimen bottle. 2. Observe the frog’s breathing in and out. 3. Release the frog back to its environment. 4. Explain the behaviour of the mouth as the frog breathes in and out. The gaseous exchange system in frogs consists of, • The moist skin. • Mouth cavity. • The lungs. The skin: Oxygen in the atmosphere dissolves into the moist, thin skin and diffuses into the dense blood capillary network below the skin. Due to its lower concentration in the blood than on the skin surface, oxygen is then transported to tissues through the red blood cells. Carbon (IV) oxide transported from the tissues diffuses into the skin’s surface and into atmosphere from the blood due to its higher concentration in the blood than on the skin surface. Fig. 4.8: Moist frog skin. Mouth cavity: Muscles of the mouth contract to lower the floor of the mouth, reducing its pressure lower than the atmospheric pressure: Air then moves in through the open nostrils into the mouth where gaseous exchange takes place in the dense blood capillary network in the mouth cavity. Oxygen diffuses into the blood and is transported by the red blood cells to tissues, while carbon (IV) oxide diffuses from the blood into the mouth cavity, where it is in lower concentration, and it is exhaled through the open nostril when the floor of the mouth is raised. The lungs: Muscles of the mouth contract and lower its floor. The volume in the mouth cavity increases, reducing the cavity pressure in the
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mouth than in the atmospheric pressure. Air rushes into the mouth cavity through the nostril due to the reduced pressure. The nostril close and the floor of the mouth is raised to force air into the lungs. Nostril Glottis Fig. 4.9: Lungs of a frog. 91 Gill filaments Gill rakers Gaseous exchange takes place between the alveoli and the blood. Oxygen diffuses into the blood where it is in lower concentration, while carbon (IV) oxide diffuses into the alveoli where it is in lower concentration, and is exhaled through the nostril by the force of the flexible lungs as they contract and relax. Did you know? Gill arch There is a frog Barbourula kalimantanensis, in Borneo Indonesia that has no lungs and breathes entirely through its skin. The facts Gaseous exchange in the gills of a bony fish The mouth opens and the floor of the mouth cavity is lowered by muscular inhalation. This contraction during increases the mouth cavity volume, and reduces mouth cavity pressure. As a result, water flows into the mouth. Meanwhile, each enclosed operculum on either side of the mouth bulges outwards to cause reduction of pressure and increase in volume of the gill cavity, so that water containing dissolved oxygen flows from the mouth cavity to the gill chamber over the gill filaments and gill lamellae. Fig. 4.10: Gills in fish. The mouth then closes and the muscles contract to raise the floor of the mouth cavity, reducing cavity volume and increasing the cavity pressure. When this is happening, the higher external pressure presses the operculum against the side of the mouth. In this case, each operculum acts as a valve to ensure that water enters only through the mouth. This forces the remaining water in the mouth to flow towards the gill chamber. the mouth has a Water entering higher concentration of oxygen which diffuses from the water flowing over the gill filaments and gill lamellae into the blood, through the thin walls of blood capillaries and gill epithelium. combines with Oxygen haemoglobin in fish blood flowing in the opposite direction to maintain a high concentration gradient, and is then transported to other parts of the body. absorbed 92 Gill rakers Gill arch Gill filaments Oxygenated blood De-oxygenated blood Gill filaments Fig. 4.11: Flow of water over the gill lamellae.
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Gills are highly vascularised to maintain a high concentration gradient in favour of oxygen diffusing into the blood and carbon (IV) oxide diffusing out. The gill filaments are thin. This reduces the distance of diffusion of the gases. Bony gill arches provide support to gill filaments. Gill rakers are bony hairlike projections on the gill bar used to filter out and prevent solid particles from entering the gills hence avoiding clogging and mechanical damage. Gill filaments are numerous and bear gill lamellae to increase surface area for gaseous exchange. The facts Human respiratory system and its functions The nostrils have goblets cells secreting mucus, which trap dust particles and pathogens, therefore cleaning the inhaled air. The nostrils also clean the air by filtering using nostril hairs. The sinuses are moist to moisten the dry inhaled air. The nostrils have numerous capillaries to warm up the cold inhaled air. The epitheliums of nostrils have olfactory cells to detect harmful chemicals in the air. The inner passages of airways is lined with mucous membrane, which contains ciliated epithelium. Cilia movement to and from cause a sweeping action of dust particles and pathogens towards the pharynx, for swallowing, hence preventing their entry into the alveoli. The mucous membranes of the trachea and bronchial tubes, contains goblet cells, which produce mucus, to trap dust particles and pathogens and prevent them from finding their way into the airways. 93 Trachea Ribs Lung Bronchus Lung inside view Rib (cut away) Diaphragm Fig. 4.12: Human respiratory system. The mucous membranes are well served with blood capillaries, which keep the incoming air warm. The mucous membranes are moist, to moisten the air therefore preventing the drying of alveoli internal surface. The epiglottis on top of the trachea,prevents food, drinks and other solid particles from going in the trachea during swallowing. The lung has numerous alveoli that provide a large surface area for efficient gaseous exchange. Epithelial lining between alveoli walls and blood capillaries is one cell thick (thin)S, to reduce the diffusion distance, therefore increasing diffusion rate and rate of gaseous exchange. The lungs are spongy, and have numerous alveoli that accommodates large volume of gases (
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oxygen). It is highly vascularised, ensuring a large concentration gradient in favour of gaseous exchange. Pulmonary arteriole Blood flow Capillary network on surface of alveolus Blood flow Pulmonary venule Fig. 4.13: Capillaries surrounding alveolus. 94 Its epithelial lining is covered by a thin layer of moisture or water film, to dissolve oxygen for easy diffusion in the blood plasma and red blood cells. To pulmonary vein Fluid CO2 Air O2 From pulmonary artery Capillary Alveolar membrane Respiratory membrane Gases can dissolve and diffuse between the lungs and the circulatory system. Oxygen diffuses into red blood cells Carbon (IV) oxide diffuses into alveolus Fig. 4.14: Gaseous exchange between alveolus and capillaries. The lung is connected to tree-like system of tubes, (the trachea and bronchi/ bronchioles), that supply oxygen and remove carbon (IV) oxide from the lungs. The whole lung is covered with the pleural membrane which is air tight thus changes in pressure within the lungs can occur without external interference. The facts How does carbon (IV) oxide that is produced in the leg muscle cell of human reach the atmosphere? Carbon (IV) oxide dissolves in the plasma, enters the red blood cells, where it reacts with water to form carbonic acid which dissociates into hydrogen carbonate. It is transported as hydrogen carbonate, or it combines with haemoglobin to form carbaminohaemoglobin and is transported as carbon (IV) oxide, then diffuse from across the capillary and alveolar walls, where it dissolves into the thin water film/moist alveoli lining, and hence to the alveoli air filled cavity, from where it is forced out during expiration, through the bronchioles, bronchi, the trachea and finally out through the nasal/buccal cavity, to the atmosphere. Cellular respiration Remember Combustion is an oxidation reaction of carbon and oxygen. Cell cytoplasm consists of cytosol and organelles. Functions of the mitochondria include provision of energy in form of Adenosine Triphosphate (ATP). 95 Group Activity 4.2 What do you observe in Figure 4.15? What are the requirements for the wood to burn? Fig. 4.15: Wood burning. What types of energy would you observe if you were the one that started
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this fire? What types of energy transformations are occurring as the wood burns? Suggest the type of molecules burning in the wood. Suggest how the burning wood molecules compare with glucose in your body cell cytoplasm. Would you put your finger in the fire? Why? What is the difference between the carbon molecules in wood burning to provide energy and the carbon molecules called glucose being broken down to provide energy? is an enzyme Cellular respiration controlled process occurring in all cells to breakdown glucose (containing chemical energy) and release energy in form of biological energy molecules Triphosphate, called carbon (IV) oxide and water. Cellular respiration occurs in the fluid part of the cytoplasm called cytosol and in the cell organelle called the mitochondrion (plural: mitochondria). enzymes Adenosine Glucose + Oxygen Carbon (IV) oxide + water + energy C6H12O6 + 6O2 6CO2 + 6H2O + energy enzymes Cellular respiration may occur in the presence of oxygen in a process called Aerobic respiration or may occur in absence of oxygen in a process called Anaerobic respiration. Respiration is also called tissue/internal respiration. Group Activity 4.3 1. Continually clench and unclench both fists with one arm drawn by your side and the other raised in the air. 2. Explain why the arm that is raised aches while the other arm does not. The facts The facts What is cellular respiration? The difference between combustion of carbon molecules in wood and breakdown of the carbon molecule called glucose in the cytoplasm of your body cells is a process called cellular respiration. Importance of energy in living organisms Why is energy important in the lives of living organisms? Energy is needed by living organisms so that they can carry out all metabolic include catabolic processes which processes and anabolic processes. These processes include; 96 • Movement and locomotion: which involves muscle contractions when moving limbs and chemotaxis of organisms. Movements to find food, mates and shelter require energy too. • Reproduction: This is the process of meiotic cell division to form gametes. The movement of gametes uses energy. • Nutrition: This involves • processes like churning of food in the stomach, chewing of food, absorption process, peristalsis, and synthesis of enzymes, which use biological energy. Irritability: Active transport of substances across cell membranes result in coordination movements like nerve impulse conduction,
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nastic movements in plants, and tropisms. • Growth and development: Formation of new cells in the process of mitotic cell division, and synthesis of proteins from amino acids. • Excretion and Homeostasis: This involves maintaining constant body temperature in homeotherms so that enzymes have optimum temperature to function in, removal of metabolic waste products like the process of deamination in the liver. • Respiration and gaseous exchange: Even the process of energy transformation requires energy for it to proceed. Breathing in and out require contraction of intercoastal muscles and diaphragm muscles. The facts Importance of respiration Why is respiration essential in living organisms? Adenosine Triphosphate is the energy currency of the cell. Respiration is the process that produces most of the Adenosine Triphosphate abbreviated as ATP. All cell activities, like active transport, require energy in form of ATP. It is the only way a cell can utilise energy. During aerobic respiration, each molecule of glucose yields a total of about 38 molecules of ATP molecules. This is an equivalent of 1,178 kJ (one molecule of ATP is equivalent to 31 kJ). The heat energy is released little by little, in stages to prevent sudden overheating of the cells. Glucose is an energy-rich molecule but it is a chemical energy that the cell cannot utilise until respiration transforms the energy into biological energy molecules. Respiration process packages energy in quantities that would not destroy the cell when released. Combustion of glucose would release energy in quantities harmful to the cell. There are two types of respiration, namely aerobic and anaerobic respiration. The facts Process of respiration The breakdown of glucose, catalysed by respiratory enzymes takes place in many steps. While some of the steps use energy, 97 others release energy and therefore ATP is synthesised. The steps may be categorised into three stages, namely glycolysis (splitting a glucose molecule into two pyruvate molecules), Krebs cycle or citric acid cycle, and electron transport system stage. Glycolysis is the only stage that is common to both aerobic respiration and anaerobic respiration. Glycolysis Glycolysis occurs in the cell cytosol which is the fluid part of the cytoplasm. Glycolysis is the breakdown of a glucose molecule into two pyruvate molecules (pyruvic acid) and production of 2 ATP molecules. The first
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step of this process requires energy as ATP to increase the free energy of the glucose molecule and convert it into fructose-1,6-diphosphate. This is called phosphorylation. This molecule has two phosphate groups and six-carbon atoms, therefore, it can be broken down into two molecules of 3 carbon sugar each also called triose sugar. The two triose sugar molecules are converted into pyruvic acid. Glucose ATP ADP Glucose 6 phosphate Activation Glucose and fructose are isomers ATP ADP Fructose 1,6 diphosphate 3 Carbon sugar phosphate 3 Carbon sugar phosphate Splitting NAD+ NADH + H+ 2ATP Oxidation Pyruvic acid (3 carbon compound) Fig. 4.16: Glycolysis flowchart. Glycolysis produces four ATP molecules and uses two ATP molecules therefore the net ATP production is two molecules and synthesis of two molecules of nicotinamide adenine dinucleotide hydrogen (NADH). Nicotinamide adenine dinucleotide is a hydrogen acceptor or carrier transferring the hydrogen ion to the electron transport system in the mitochondria. 98 The fate of pyruvic acid is depended on the availability of oxygen. If oxygen is present, pyruvic acid is converted into a 2-carbon compound called acetyl coenzyme A. It can then proceed to the Krebs cycle inside the matrix of the mitochondrion. If oxygen is absent, then pyruvic acid under goes anaerobic respiration without further energy production. In human muscles and other animals, anaerobic respiration produces lactic acid, whereas plants and yeast cells produce ethanol and carbon (IV) oxide. Fig. 4.17: Alcoholic and lactic fermentation. Did you know? The facts Your muscle cells have the ability to respire for a short time without oxygen using anaerobic respiration. Using this reaction, glucose that has been stored in your muscle cells is converted into lactic acid. This is what made your raised arm ache in Group Activity 4.3 Aerobic and anaerobic respiration Work to do What are the differences between aerobic and anaerobic respiration? 99 Group Activity 4.4: Complete the table below on the differences between aerobic and anaerobic respiration Question Aerobic respiration Anaerobic respiration Where does it occur? Cytosol and mitochondria. Cytosol only. What is glucose broken down into? How many molecules of ATP are
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produced? 38 molecules of ATP from each molecule of glucose. Are there further reactions? For how long can the reaction occur in your body? How fast is ATP production process? Is oxygen needed? How efficient is it? Did you know? Yes 40% Carbon (IV) oxide and Ethanol in plants or yeast, and lactic acid in animals or bacteria. Ethanol and lactic acid can be broken down further in the presence of oxygen. Fast No 2% Most cars have a fuel combustion efficiency of about 20-25%. Therefore, aerobic respiration has doubled the efficiency of cars. Check your progress 4a Copy the flow diagram in Fgure 4.18 below and complete the terms used to compare aerobic and anaerobic respiration. Respiration (ia) (ib) Breakdown of g_______ with the help of e_______ Oxygen present Oxygen _____ (iii) (iv) __ respiration (v) __ respiration Animals Plants Animals Plants (vi) Energy transferred to ATP or released as h_______ (vii) Produces I_______ acid (poisonous to animals) (viii) Produces e_______ (poisonous to plants) Fig. 4.18: Flow diagram of aerobic and anaerobic respiration. 100 Role of oxygen in respiration After glucose is converted into pyruvic acid, oxygen is required so that the pyruvic acid can move to the next stage and be converted to acetyl-CoA. Acetyl- CoA enters the mitochondria matrix where enzymes break it down in the Krebs cycle to release energy and some of the energy is used to move hydrogen ions to the intermembrane space in the electron transport system. The accumulated hydrogen ions move back (a process called Chemiosmosis) to the matrix via the ATP synthase enzyme which uses oxygen to form water and release about 34 ATP molecules. From one molecule of glucose a total of 38 molecules of ATP are synthesised (2ATP molecules from Glycolysis, 2 ATP molecules from the Krebs’ cycle and 34 ATP molecules from the electron transport system). Cristae Inner membrane Inter membrane space Outer membrane Cristae Matrix ribosomes F1 (ATP synthase particles) Fig. 4.19: Mitochondrion During strenuous exercise like when you run 100 metres race, the demand for ATP is higher than the supply of oxygen, therefore, the muscle cells respire anaerobically and produce lactic acid. The accumulation of lactic acid
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in the muscles would change the pH of the tissue fluid around the muscle cells and is therefore toxic and can cause cramps. Faster heartbeat after the running quickly carries the blood containing lactic acid to the liver where it is oxidised to carbon (IV) oxide and water by the lactic acid dehydrogenase enzyme or into pyruvic acid. The quantity of extra oxygen required to break down the lactic acid is called “oxygen debt”. The extra oxygen is supplied during the rapid and deep breathing called panting, after intense physical exercise. 101 The facts Stages of aerobic respiration Aerobic respiration is a complex enzyme-driven biochemical process that takes place in the presence of oxygen in the living cells, resulting in the release of energy, carbon (IV) oxide and water. Aerobic respiration is a very complex biochemical process involving three main stages. These are: Stage I: Glycolysis Stage II: Citric acid cycle (Krebs Cycle) Stage III: Electron transport system Krebs’ cycle (Stage II): in this cycle pyruvic acid, in presence of oxygen, is broken down to carbon (IV) oxide and hydrogen ions. Summary of the Krebs’ cycle is: 2 Pyruvic acid + 8NAD + 2FAD + 2ADP 6CO2 + 8NADH + 2FADH2 + 2ATP III Electron transport system: This is a very complex system involving the transfer of the hydrogen ions through several types of acceptor molecules like NAD (nicotinamide adenine dinucleotide) which forms NADH2 and FADH2 (Flavin adenine dinucleotide hydrogen). Their hydrogen ion is taken up by oxygen to form water resulting in energy release. This energy is taken up by ADP to form 34 molecules of ATP per molecule of glucose. This process occurs in the ATP synthase in the granules attached on the cristae. Fig. 4.20: Summary of aerobic respiration stages. 102 Did you know? Hydrogen carriers NAD and FAD are derived from vitamin B complex and are called coenzymes. Check your progress 4b 1. Why is pyruvic acid converted into alcohol or lactic acid during fermentation? 2. Why is there less release of energy during anaerobic respiration? 3. List the three phases of aerobic respiration of glucose. Where in the cell do these reactions take place? 4. What is the role of oxygen
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in aerobic respiration? 5. Name the substrate and products of the Krebs’ cycle. 6. How do fatty acids enter the Krebs’ cycle? Factors affecting the rate of respiration • Temperature affects all chemical and enzyme driven reactions. Low temperatures below optimum slow down the rate of respiration while temperatures optimum denature the respiratory enzymes. the At optimum respiration rate is highest. temperature above • Molecular oxygen is the final acceptor of electrons in the electron transport chain, as the oxygen concentration increases from zero, the rate of aerobic respiration increases. rate of respiration. • tissues • Hydration increase of germinating increases rate of seed respiration. Inorganic ions uptake in plants from respiration requires ATP therefore plants increase the rate of respiration when absorbing mineral ions. • Other chemicals like cyanides, carbon II oxide, inhibit the rate of respiration. • Wounding a tissue causes an increase in the respiration rate of cells close to the wound. • Age and type of tissue, with young and developing tissues respires more vigorously than mature tissues. Enzymes Practical Activity 4.4: To demonstrate the presence of Enzymes in cells. Requirements • Basin • Conical flask • Syringe • Delivery tube • Pestle and mortar • Measuring cylinder • Water • Hydrogen peroxide • Petroleum jelly • Stop watch • Water trough • Raw Irish potato • Carbon IV oxide concentration, increase in the tissues retards the 103 Plunger Syringe Raw Irish potato paste Cork Conical flask Hydrogen peroxide solution + Irish potato paste Measuring cylinder 25 ml Clamp Water Trough Delivery tube Rubber tubing Fig. 4.21: Setup for demonstrating presence and actions of enzymes in cells. 1. Set the apparatus as show in fig 4.21 above. 2. In a 500 ml conical flask, add 30 ml hydrogen peroxide solution. 3. Fix the cork securely in the flask. 4. Half-fill the water trough, small basin or sink with water. 5. Fill three 25ml measuring cylinders with water. Invert them over the basin of water. Have one with the open end under the surface of the water in the basin and with the end of the rubber tubing in the measuring cylinder then use a clamp to hold it in place. 6. Peel an Irish potato then chop it up to small pieces. Place the pieces in a mortar and grind them to a fine paste using the pestle. 7. Use a 20 ml syringe to measure of potato paste.
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8. Put the syringe in place in the cork of the flask but do not push the plunger as yet. WAIT. 9. Apply petroleum jelly at all joints of the setup. 10. Push the plunger of the syringe with the potato paste to add 1 ml paste into the hydrogen peroxide and immediately start the stop watch. 104 11. After 20 seconds, make a reading of the volume of oxygen gas in the measuring cylinder and create a table to record your readings. 12. Push the plunger of the syringe with the potato paste to add 2 ml paste into the hydrogen peroxide and immediately start the stop watch and after 20 seconds make a reading. • Push the plunger of the syringe with the potato paste to add 3 ml, then 4 ml, then 5 ml; upto 10 ml paste into the hydrogen peroxide and immediately start the stop watch and after 20 seconds make a reading. (After the first measuring cylinder is full of oxygen replace it with another one). • Calculate the rate of oxygen production in cm3/s. • Plot a graph of rate of oxygen production against potato paste volume. Suggest what the potato paste represents. (Hint: From your Chemistry lessons, how do you produce oxygen using hydrogen peroxide?) is a Note: Hydrogen peroxide poisonous to substance accumulate in the body. It is, therefor,e broken down to water and oxygen by the catalase enzyme. left if Group discussion 1. Suggest the reactants in this experiment and the products too. 2. How would you confirm that the gas produced is oxygen? Did you confirm? 3. Identify any inconsistencies in your results. 4. Describe the shape of the graph and explain the shape of the graph in relevant biological terms. 5. Describe any technical difficulties you had with this apparatus and explain how these could be overcome. 6 Design a similar experiment and demonstrate to investigate the presence of the catalase enzyme in liver or yeast cells. The facts Enzymes are protein catalysts which increase the rate of biochemical reactions by lowering the activation energy. Catalysts have the following properties; • Catalysts increase the rate of chemical reactions. • Catalysts are not used up in the reactions therefore they are recycled. • Catalysts are not changed at the end of the reactions. Protein catalysts referred to as enzymes are made of amino acids joined by peptide bonds to form long polypeptide chains that fold into a unique threefunctional dimensional shape. The 105
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parts of enzymes are called active sites and catalytic abilities. The reacting molecules called substrates have to fix into the active sites for the enzyme to work on them and form a temporally enzyme-substrate complex. Substrate Active sites Enzymes Enzyme-substrate complex Fig. 4.22: Enzyme-substrate complex formation. Hydrogen peroxide left in an open beaker for a few days would dissociate into water and oxygen. But what did you notice when you placed pieces of liver, potato, or yeast in a beaker containing peroxide, the reaction was very fast as the enzyme catalase breaks down hydrogen peroxide into oxygen and water. The oxygen gas was trapped by the fluid to form bubbles filling the beaker. The reaction is speeded up over 100 billion times. Enzymes Hydrogen peroxide Oxygen Fig. 4.23: Reactions of catalase enzyme and Hydrogen peroxide. Water The active site has a definite shape and therefore the enzyme is very specific on the substrate it can synthesis or break down. The catalase enzyme cannot break down sucrose. The enzyme and substrate work like a key and lock. 106 Substrate Enzyme Active sites The substrate and enzyme active sites have complementary shapes Enzyme-substrate complex The characteristics of enzymes Fig. 4.24: Enzyme active sites are specific. Temperature: Most enzymes function best within a certain range of temperature, called optimum temperature. Lower than optimum temperatures inactivates enzymes because the substrate has low kinetic energy, while higher than optimum temperature denatures enzymes by deforming the active sites. Heat energy causes more collisions between enzyme and substrate 37oC Enzymes denature at high temperatures so rate falls rapidly Optimum temperature for humans is close to 37oC Temperature 37o C Fig. 4.25: Effect of temperature on enzymes in humans. Sensitive to pH changes: Enzymes work best at a specific optimum pH. Some work best in alkaline, others in acidic, while some in neutral media. When the pH is below or above the optimum the enzyme is denatured. 107 Salivary amylase Pepsin Pancreatic lipase Acidic 2 3 4 5 6 pH 7 8 9 10 11 12 Basic Fig. 4.26: Effect of pH on enzyme activity. Specificity: Particular enzymes act on specific substrates, like carbohydrase on carbohydrates, lipase on lipids and protease on proteins. Examples enzymes involved in respiration • Hexokinase converts
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glucose to glucose-6-phosphate by adding a phosphate group. • Hexose phosphate isomerase converts glucose-6-phosphate to fructose-6-phosphate. • Dehydrogenase removes hydrogen ions from various molecules. • Aldolase splits the fructose -1,6-diphosphate (6-carbon) to 3-phosphoglyceraldehyde (triose sugar). • ATP synthase is involved in the synthesis of ATP in the cristae. • Decarboxylase releases or removes • carbon (IV) oxide. Lactic acid dehydrogenase breaks down lactic acid to water and carbon (IV) oxide in the liver in the presence of oxygen. Reversibility: Enzymes can cause reactions to follow any direction, depending on the concentration of substrates, reactants and products. Carbonic anhydrase CO2 + H2O Water Carbon (IV) oxide H2CO3 Carbonic acid Fig. 4.27: Reversible action of carbonic anhydrase in different concentrations of substrate, reactants and products. Enzymes are not used up in the reaction that they control: that is, they do not form parts of the products thus they can be used again. 108 Fructose Glucose Enzyme (sucrase) Active site Enzyme (sucrose) 1 4 Products are released Enzyme and substrate are available Enzyme substrate complex 3 Substrate is converted to products 2 Substrate binds to enzyme Anaerobic respiration experiments Fig. 4.27: Enzyme is recycled. Conduct experiments to investigate anaerobic respiration involving yeast, fungi and germinating peas or beans. Remember Fig 4.28: Yeast cells Yeast are unicellular eukaryotic fungi from the Kingdom Mycota. They require energy to carry out metabolic activities. Through cellular respiration, they obtain the energy from carbohydrates like sucrose. 109 Yeasts are facultative anaerobes, therefore, in the presence of oxygen, yeasts will respire aerobically to completely break down carbohydrates into carbon (IV) oxide and water releasing energy. When given the choice, yeasts will do aerobic respiration because the ATP yield is more than anaerobic respiration. When oxygen is absent, yeast can use anaerobic respiration in a process called alcohol fermentation. In aerobic respiration, they partially break down carbohydrates and produce carbon (IV) oxide and ethanol (C2H5OH
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). The carbon (IV) oxide produced turns limewater cloudy. Air dissolved in sucrose solution can be expelled by boiling and the yeasts are killed by boiling at 100° C. Tap Capillary tube Beaker Boiling tube Limewater Yeast + sucrose (Solution A) Rubber cork Rubber tubing Capillary tube Test tube Boiling tube Boiled yeast + sucrose (Soluion B) Limewater Water bath at 40o C Fig. 4.29: Experiment setup Practical Activity 4.5: To investigage anaerobic respiration involving yeast Requirements • Hot water source 1,000 ml beaker • 2 boiling tubes • 2 test tubes • 2 grams of dried yeast • 110 • • 2 ml of yeast boiled at 100 – 150° C for 20 minutes in an oven. 10 ml of 5% sucrose solution made with boiled water. Tap water should be boiled for 30 minutes to expel dissolved gases. Dissolve the sucrose in the boiled water while still warm and without shaking and store the solution in stoppered volumetric flasks. • • • • 15 cm3 limewater 2 ml cooking oil 2 labels for labelling the boiling tubes 2 containers for living and dead yeast 2 droppers • 20 ml syringe. • • Thermometer Procedure 1. Place about 20 ml limewater into each of the two test tubes. 2. Label the two boiling tubes solution A and B respectively. 3. In boiling tube A, add 1 gram of dried yeast. 4. In boiling tube B, add 1gram of boiled yeast at 100–150°C. 5. Draw 10 ml of sucrose solution using a syringe and add to each boiling tube ensure the mouth of the syringe touches the side of the boiling tube to prevent introduction of air. You should avoid shaking the solution. 6. Using a dropper draw cooking oil and place five drops of oil in the mixture in each boiling tube. 7. Fit the rubber corks with the delivery tubes as in Figure 4.30. 8. Half fill-the 1,000 ml beaker with hot water at about 40 °C use the thermometer to measure temperature and add cold water if too hot. 9. Dip the two boiling tubes in the warm water bath and their respective delivery tubes other ends into the test tubes containing limewater. Group discussion Discuss the following questions and answer them in your notebooks then have the group leader present your findings to the rest of the class. 1. What do you observe in the limewater and the boiling
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tubes? Why? 2. Would your observation agree with hypothesis that yeast’s respire anaerobically? 3. How has this experiment ensured that the evidence of respiration is because of yeast anaerobic respiration and not anything else? 4. What assumptions have you made in this experiment? 5. How will you setup a control experiment for the observations made in limewater? 6. Evaluate this experiment and suggest how the design was done to ensure anaerobic respiration occurred. 7. Suggest what else you could use instead of sucrose and why. 8. How would you use this knowledge in the real world? 9. Suggest changes you would make to this experiment to investigate aerobic respiration in yeast. Remember The combination of sodium hydroxide and pyrogallic acid (sodium pyrogallate) absorbs oxygen and carbon (IV) oxide from the atmosphere. 111 Practical Activity 4.6 Requirements per group • 2 rubber bungs with a hole same fitting as the capillary tube • Petroleum jelly 2 labels • • Thread • • • • • • • • • • • 2 conical flasks Scissors 2 × 30 cm long capillary tube of about 0.5 mm bore size 20 ml measuring cylinder 5 ml test tube 2 ml sodium hydroxide 2 × 200 ml beakers 4 ml pyrogallic acid 20 certified bean seeds soaked overnight (From Seed company) 20 dried beans Permanent marker pen Sodium pyrogallate Conical flask Sodium pyrogallate Bent glass tubes Cork Thread Small test tube (A) Respiring seeds Water Dry seeds (B) Fig. 4.30: Anaerobic respiration of germinating seeds. Procedure 1. Label two conical flasks A and B. 2. 3. In conical flask A, place 20 sprouting beans after overnight soaking. In conical flask B, place 20 dried beans (not soaked). 112 4. Tie each of 5 ml test tube with a thread long enough to suspend the test tube over the beans. 5. Then measure 1 ml of sodium hydroxide solution and place into each of 5 ml test tubes. CAUTION: Wash off any sodium hydroxide on your skin with lots of water. 6. Add 2 ml of pyrogallic acid to each of the test tubes and do not shake. It will turn dark brown or black. 7. Place the test tube containing the mixture of sodium hydroxide and pyrogallic acid in the conical flask and let it hang from the rubber as
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per the Figure 4.31. 8. Connect the capillary tube and insert in a beaker half full of water. 9. Use a permanent marker pen to mark the level of water in the capillary tubing. 10. Apply petroleum jelly at all fixings joints. 11. Leave both flasks in a warm place for 48 hours. 12. At the end of two days, note how many seeds germinated in each flask in an appropriate table. 13. Copy the table below and record your observations. Conical flask Observation after 48 hours A B Group discussion 1. Suggest the aim of this experiment. 2. Supposing you were asked to state the hypothesis of this experiment, what would you state? Why? 3. How do you explain the observations you have made? 4. Why did you setup two conical flasks A and B? 5. How would you design an experiment to demonstrate that germinating seeds produce carbon IV oxide? 6. How is the knowledge you have gained here used in real world? 7. Prepare a presentation of your findings then have one member present to the class. Economic and industry applications of anaerobic respiration (fermentation) Alcoholic and lactic fermentation is economically beneficial in several ways: • Baking industry: In bread-making, yeast is mixed into the dough and when the carbon (IV) oxide is heated during baking, it expands and escapes and leaves behind the small holes that give bread its light and spongy texture. • Alcohol production: In beermaking, beer is made from germinating grains, for example, barley and in wine-making, juices from crushed plant parts are mixed with yeast in anaerobic conditions. • Biogas production: Biogas is produced using methanol a form of alcoholic fermentation. 113 • Gasohol production: Gasohol is produced using ethanol from alcoholic fermentation. Lactic fermentation • Cheese production: Bacteria like Streptococcus lactis are added to pasteurised milk. The bacteria converts galactose to lactic acid which curdles the milk. The curd is hardened and flavoured to form cheese. • Yoghurt making: Yoghurt is made from milk which is treated with Streptococcus bacteria. This form lactic acid and so cause the milk to curdle. Silage production: Lactic acid produced in lactic fermentation is used to preserve forage for livestock. • The facts 4.2 Carbon cycle Carbon cycle is a biogeochemical
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cycle showing how carbon circulates between the living organisms (biotic) and their environment (abiotic). Practical Activity 4.7: Investigating the presence of carbon (IV) oxide in a living organism Requirements • Eye protection gear • Crushed natural chalk • Vinegar (or hydrochloric acid) • Flask • Balloon • Test tube 114 • Limewater (calcium hydroxide solution) Caution: Wear eye protection. Procedure 1. Pour limewater into a test tube. 2. Place crushed chalk into a flask and add vinegar (or hydrochloric acid) to the flask. 3. Place a deflated balloon tightly over the flask neck so that no gas can escape. 4. When the reaction has stopped, pinch the balloon tightly at the balloon neck, so that no gas escapes. 5. Remove the balloon from the flask and place it over to the test tube. Then squeeze it so that the gas goes into the limewater. Observe record what happens. and Alternatively, you can breathe out into lime water using a straw. Group discussion 1. What colour was the limewater before the reaction? 2. What happened to the limewater when you added the gas from the balloon? 3. Where did the gas in the balloon come from? 4. What reaction was responsible for creating it? 5. What gas was released from the chalk by the reaction? 6. Look at the diagram below and answer the questions that follow: Pool of CO2 in atmosphere Respiration Respiration Respiration Combustion CO2 Hydrogen carbonate CO2 Photosynthesis Decay organisms Respiration Death Carbonate, that is, limestones Decay organisms Death Peat Coal Oil and fuels Fig. 4.31: The Carbon cycle. (a) What processes are involved in the carbon cycle? (b) How are these processes interrelated? (c) Identify processes that: • Increase carbon (IV) oxide into the atmosphere. • Reduce carbon (IV) oxide from the atmosphere. (d) Which human activities increase the amount of carbon (IV) oxide in the atmosphere? 115 Photosynthesis The facts Fig. 4.32: Simple carbon cycle. There are five main reservoirs of carbon on Earth. In order from the largest to the smallest reservoirs, they include: decomposed to release carbon (IV) oxide to the atmosphere from the soil organic matter. Soil and fossil fuels • Oceans • • Atmosphere • Organisms The atmosphere is the main pool of carbon IV oxide and organisms exchange with it. Through the following
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processes, organisms exchange carbon with their environment: • Respiration: The living plants, decomposers and animals respire, therefore, release carbon (IV) oxide to the atmosphere. • • Deforestation for charcoal and firewood: Firewood and charcoal burning and use release carbon (IV) oxide to the atmosphere and reduce the number of trees using carbon (IV) oxide from the atmosphere. Fossil fuel combustion: About 299 – 300 million years ago, massive organic matter was buried before it could decompose. Consequently, fossil fuels like coal, oil and natural gas were formed. Their combustion today releases carbon (IV) oxide to the atmosphere significantly. • Decomposition: Living plants, • Diffusion: Carbon (IV) oxide animals and decomposers die and their waste materials are reacts with water and diffuses into the ocean as hydrogen carbonate. Aquatic life respire and release 116 carbon (IV) oxide that too reacts with water forming hydrogen carbonate. Calcium carbonate shells of dead marine life form limestone after geological forces act on them. • Photosynthesis: Green plants use carbon (IV) oxide from the atmosphere in photosynthesis while aquatic green plants and phytoplankton use hydrogen carbonate from the ocean water in photosynthesis. Fig. 4.33: Simple carbon cycle. Group activity 4.5 Reducing your personal carbon footprint. 1. Find out ten easy and practical things you can do in personal space, at your school, home, village, estate and town to help stop global warming. 2. What are you doing at your personal level that is adversely affecting the carbon cycle? 3. What can you do to reduce your carbon footprint? Carbon (IV) oxide and the global warming. Fossil fuels combustion has increased the quantity of carbon (IV) oxide in the atmosphere. Global warming is expected to happen due to carbon (IV) oxide and other greenhouse gases. Compensation point Just before dawn when there is very little light, the rate of photosynthesis is low. The plant cells are respiring and producing carbon IV oxide. The rate of respiration at this time is higher than the rate of photosynthesis. Therefore, its rate of release of carbon IV oxide is higher than its rate of consumption. 117 As light intensity increases, the rate of photosynthesis increases, and the amount of carbon (IV) oxide being used also increases. A point is reached when the rate of photosynthesis becomes equal to the rate of respiration. The rate of release of carbon (IV) oxide by
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respiration is the same as the rate of consumption of carbon (IV) oxide (by photosynthesis). This point at which the rate of respiration is equal to that of photosynthesis is called compensation point. In most plants, compensation point is reached at around dawn. Carbon IV oxide uptake C B A Carbon (IV) oxide release Light intensity Respiration only occuring in the absence of light Fig. 4.34: Graph illustrating the compensation point. From the graph, at point: A: Respiration rate is high and carbon IV oxide release is high. A – B: Increasing light intensity and photosynthesis commences. Carbon (IV) oxide uptake increases whereas release of CO2 reduces. B: Compensation point. Rate of photosynthesis is equal to rate of respiration and therefore rate of CO2 uptake equals rate of its release to the atmosphere. is B – C: Rate of photosynthesis much higher than rate of respiration, therefore, rate of uptake of carbon (IV) oxide is more than rate of release of carbon (IV) oxide. Group Activity 4.6 Study the photosynthesis and cellular respiration equations below. Solar energy Photosynthesis CO2 + 6H2O C6 H12O6 + O2 Cellular respiration Chemical energy (ATP) + heat 1. What do you observe? 2. What does that mean to the carbon cycle? 3. What do you think would happen if a plant was to be in this state for a long period of time? Why? 4. Suggest how nature avoids this condition? 5. Write an essay titled “Compensation point in plants” then read it to rest of the class. 118 Check your progress 4c 1. Define respiration. 2. What is the role of O2 in electron transport chain? 3. How many molecules of ATP are released when a molecule of glucose is oxidised to (a) CO2 and H2O? (b) Ethanol and CO2? 4. Name the end products of electron transport chains. 5. Respiration is a continuous process in green plants. Then why is it that they give out O2 and not CO2 during the day? 6. What is for the site (a) Glycolysis, (b) Krebs’ cycle, (c) ATP generation by oxidative phosphorylation? 7. What is the fate of pyruvic acid in the (a) presence, and (b) absence of oxygen? Write the equations representing the processes, that
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take place in (a) and (b). 8. What is the significance of stepwise oxidation of organic molecules instead of one step reaction? is photorespiration? the significance of 9. What 10. List the substrates that enter and the products produced in (a) glycolysis (b) Krebs cycle 11. How is yeast useful in industry? Give any three examples. 12. How does exchange of respiratory gases take place in plants? 13. Mention the significance of TCA cycle. 14. Why does fermentation yield less energy than aerobic respiration? 15. What are the three major phases of glycolysis? 16. What is the importance of the Krebs’ cycle? 17. Differentiate between aerobic and anaerobic respiration. 18. Which of the following statements best describes the process of respiration? Respiration in living organisms is: (A) the intake of oxygen and output of carbon dioxide (B) the intake of food and the output of energy (C) the intake of food and the release of carbon dioxide (D) the breakdown of food to release energy (E) the oxidation of food to carbon dioxide. 19. Explain what an oxygen debt is and how it is caused. 20. When a carbohydrate is oxidised to carbon dioxide and water in the body, 21 kJ energy is produced for every litre of oxygen used. In an experiment, a girl absorbed 2 litres of oxygen in minutes. What is her energy production in kilojoules per hour? 21. The process of respiration is often summarised by the equation: C6H12O6 + 6O2 + 2,830 kJ 6CO2 + 6H2O 119 On the basis of this equation, what would you regard as acceptable evidence that respiration was taking place in a sample of living tissue? 22. A learner sets up an experiment to try and demonstrate that locusts are respiring. The diagram below shows the apparatus used. After 15 minutes, the limewater had gone milky and the learner claims that this proves that the locusts are respiring. Criticise the design of the experiment and show how you would improve it. 23. The table below shows the energy used up each day either as kilojoules per kilogram of body mass or as kilojoules per square metre of body surface. kJ per day mass/kg 128.0 per kg body mass 80 per m2 body surface 4510 64
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.3 15.2 0.018 134 216 2736 4360 4347 4971 Pig Human Dog Mouse (a) According to the table, what is the total amount of energy used each day by (i) a human being? (ii) a mouse? (b) Which of these two shows a greater rate of respiration in the body cells? (c) Why do you think there is so little difference in the energy expenditure per square metre of body surface? 120 Sodium hydroxide solutionLocust Unit The digestive and circulatory 5 systems in animals Knowledge and understanding Skills Attitudes Learning outcomes • Explain the structure and function of the digestive and circulatory systems. • • • Explain the effect of exercise on the heartbeat. Investigate the action of digestive enzymes. Identify the role of chemical and physical processes of digestion. • Appreciate the role of blood in protecting the body from diseases. • Understand the important role of glands and organs. Describe the functions of the rhythmic movement of food. Introduction What did you eat for breakfast, lunch or dinner yesterday? Did you eat the same type of food? Why did you eat different types of food? Why do you eat food? When you say that a meal was mouth-watering, what does that mean in biological terms? What happens to food after you put it into your mouth? Referring to this book, research what happens to food at each stage of its journey through the human digestive system. Prepare a role play or a storyboard with your group to show what you have found out. For example, Stage 1: Here in the mouth, I am being cut and chewed into small pieces while being mixed with lots of liquid. I am starting to feel sweeter. 121 Nasal cavity Buccal cavity Liver Gall bladder Bile duct Large intestine Appendix Caecum Oesophagus Stomach Pancreas Duodenum Ileum Rectum Sphincter muscles Fig. 5.1: The human digestive system. Which parts of the digestive system will come into contact with the food and in what order? When you eat food, it is because your body needs food to function and perform the characteristics of living organisms namely; movement and locomotion, respiration, irritability, growth and development, excretion and reproduction as well as finding food and feeding. The food you eat will get into your mouth, you chew it while your tongue mixes it with saliva and forms it into a bolus. Then you swallow it into the oesophagus and
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it is delivered to the stomach. After the stomach the food will be moved along the intestines and remaining undigested food is egested. 5.1 Digestion in animals How does the process of digestion occur in animals? Human digestive system Practical Activity 5.1 You are provided with the following items: • Any starchy foods like cassava, millet, bread, injera, rice or asida • Knife • A means of timing Iodine solution • Procedure 1. Cut a small cube of the food about 1 cm cube using a clean knife. 122 2. Put it in your own mouth of course observing hygienic conditions. 3. Without swallowing the saliva chew the food for about 30 seconds. Describe the taste of food in your mouth at the start of chewing and after the 30 seconds. 4. After the 30 seconds of chewing spit out a tiny amount of the food into a beaker or on a white tile. 5. Add two drops of iodine solution onto the chewed food. What do you observe? What colour do you observe and why? 6. Without swallowing, proceed to chew the remaining food for another 3 minutes then spit a tiny amount of food on the white tile and add iodine solution. What do you observe and what colour do you observe? Is the colour different and why? What caused the change of taste over time? (You may swallow the rest of the food) 7. Using a drawing illustrate the physical change that has occurred to the food as you chewed it. Would you suggest the name of this process? Why is the process important? 8. Write a word equation for the chemical change that has occurred to the food. 9. Cut another small cube of the food and add iodine solution to it. What do you observe? What colour do you observe and why? As a scientist, why is this part of investigation important? 10. How would you report the findings of this investigation? 11. Why are the findings of this investigations important to you as a biologist? The facts Digestion is the breakdown of complex food substances to simple absorbable molecules. Digestion in the mouth Digestion in the mouth is both mechanical and chemical. Inside the mouth cavity, food is lubricated by mucus from the saliva and chewed by the teeth. This is mechanical digestion. The tongue pushes food between the teeth for chewing and mixes the food with saliva so as to make it softer; and make it easy to swallow. Sublingual gland Parotid gland Sub
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mandibular gland Fig. 5.2: Salivary glands 123 Did you know? A healthy average person secretes about 1 litre of saliva every day (equivalent to 3 standard bottles of soda a day or 21 bottles in a week). Saliva also contains an enzyme salivary amylase which begins the extracellular chemical digestion of starch even before the food is swallowed. The enzyme salivary amylase breaks down starch to maltose (a sweet sugar). Mouth has four types of teeth: • Incisors have sharp edges for cutting. • Canines are pointed for holding food. • Premolars and molars have rigged and flattened cusps for grinding. Soft pallet Fig. 5.3: Human teeth Did you know? If you swallowed food while standing on your head, the food would move through the digestive system? The chewed food is then formed into a bolus and is pushed to the pharynx by the action of the tongue in the swallowing process. Food Tongue Epiglottis Trachea Pharynx A B C Fig. 5.4: Swallowing of food bolus. A: The food is chewed and formed into a bolus in the mouth. B: Swallowing begins as the tongue pushes food into the pharynx. C: As the soft pallet rises to close passage to the nasal cavity, the epiglottis tends to close off the trachea and open the oesophagus. The act of swallowing forces food into the oesophagus (gullet). The food is forced down the oesophagus towards the stomach by peristalsis which is a process of the 124 smooth muscles contracting and relaxing in a wave-like rhythmic movement. The food passes into the stomach via the cardiac sphincter. Gullet Contraction of gullet muscles First position of bolus Contraction of muscles Second position of bolus Fig. 5.5: Peristalsis of the oesophagus. Practical Activity 5.2 Your group is provided with the following: • White tile or spot plate • Wall clock (for the class) • 10 or 20 ml measuring cylinder or syringe • 250 cm3 beaker • Dropper • 11 test tubes • 2 test tube racks • 11 labels • 1% starch solution (about 50 ml) • 0.05 M sodium carbonate solution (10 ml) 0.1 M ethanoic acid (10 ml) Iod
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ine solution (10 ml) pH universal indicator Standard colour chart • • • • pH range Description Colour Strong acid Red < 3 3 – 6 Weak acid Orange or yellow Green Neutral 7 8 – 11 Weak base Blue >11 Strong base Violet or indigo Fig 5.6 pH colour chart Procedure 1. Wash the test tubes, beaker and droppers provided before use. 2. Use the labels provided to label the five test tubes A and B and C and D and E.(ensure the test tubes are dry before sticking the labels). 3. Using the measuring cylinder, place 5 ml of 1% starch solution in all the five test tubes. 4. Add ethanoic or sodium carbonate to each test tube as according to the table below. Clean the measuring cylinder after using it to measure sodium carbonate solution and before adding ethanoic acid. Test tube Starch solution and amylase plus A B C D E 1 ml sodium carbonate solution 0.5 ml sodium carbonate solution Nothing 2 ml ethanoic acid 4 ml ethanoic acid 125 5. Label six test tubes 1-6 and add 2 ml of universal indicator solution in each of them. 6. Drop five drops of iodine solution on five separate spots on the spot plate or white tile. 7. Measure and add 1 ml of amylase solution to all the six test tubes then shake well by hold the test tube with the index finger and thumb then stroking it. Fig. 5.7 Holding a test tube. 8. Clean a dropper and draw out a sample from each test tube in turn and drop the sample on a white tile or spot plate containing iodine solution. Step 1 Starch solution + amylase solution Dropper Step 2 your hand Iodine Fig. 5.8: Procedure of the testing. 9. Using a clean dropper each time, continue sampling at intervals. When a sample fails to give a blue-black colour with iodine solution, note the time and stop taking samples from that particular test tube. What colour do you observe? 10. If after fifteen minutes some samples are still giving a blue-black colour with iodine solution, there is little point in continuing to test the mixture in these test tubes. 126 11. Clean the dropper and use it to draw a sample from test tube A. Add 3 drops into one test tube containing universal indicator. 12. Compare the colour produced in the test tube with the standard chart provided. 13. Repeat this for each test tube, cleaning the dropper between samples
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. 14. Wash your mouth of food particles with clean safe water and spit into test tube labelled 6 containing universal indicator to test the pH of your mouth. 15. What was the pH in your mouth? Why is this important? 16. Enter your observations in the table below. Table 5.1 Table of results Tube Starch solution and amylase plus: pH Time for blue-black colour to cease appearing A B C D E 1 ml sodium carbonate solution 0.5 ml sodium carbonate solution Nothing 2 ml ethanoic acid 4 ml ethanoic acid Group discussion In your group, discuss the following questions: 1. Why did you add the mixture of starch and amylase to iodine solution? 2. What did you observe? Why? 3. In which test tube was the reaction between starch and amylase the fastest? What was the pH of the mixture in the test tube? How does that pH of the mixture in that particular test tube compare with pH of your saliva? Explain. 4. In a scenario where you have eaten starch containing food, what would happen to the starch-amylase reaction in the stomach? Why? How would you prove that? 5. Sodium carbonate and ethanoic acid altered the pH of the mixture. Suggest how else they could affect the starch-amylase reaction. 6. How else would you design the experiment to eliminate the probability of Sodium carbonate and ethanoic acid affecting the starch-amylase reaction in any other way except through pH change. 7. Write 200 words report of this Practical Activity 5.2 and submit to your teacher to comment. 127 Digestion in the stomach (monogastric digestion) Stomach is a muscular bag that stores food consisting of longitudinal and circular muscles that contract and relax (peristalsis) to churn the food into semi-fluid chyme. Stomach Did you know? Borborygmic is the stomach rumbling which happens all the time, but gets louder when your stomach is empty. Guess why? Oesophagus Gall bladder Bile duct Duodenum Fig. 5.9: Stomach The stomach also contains gastric glands which secrete gastric juice which contains hydrochloric acid. The role of hydrochloric acid in gastric juice includes: • • Neutralises the slightly alkaline pH of saliva from the mouth. Provides optimum pH for the enzymes in the gastric juice. • Kills pathogens or bacteria that may be present in the food. •
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Activates conversion of pepsinogen into pepsin. the enzyme • Denatures the salivary amylase. In the stomach of infants and young ruminants, rennin curdles milk increasing its surface area for digestion by pepsin. Gastrin hormone gastric glands in the stomach wall to secrete stomach. into gastric stimulates juice the the 128 Digestion in human small intestines The small intestine consists of the duodenum and the ileum which is relatively long and coiled to provide a large surface area and slow down the speed of movement of food therefore allowing more time for digestion and absorption of digested food products. The opening of ducts allow the bile from the liver and pancreatic juice from the pancrease into duodenum. Secretin hormone stimulates the pancreas to secrete pancreatic juice into the duodenum. Cholecystokinin stimulates the secretion of bile from the gall bladder into the duodenum. Did you know? The large intestine is about 1.5 metres while the small intestine is about 6.9 metres long and adult female’s small intestine is longer than the average adult male’s. Goblet cells in the intestinal wall produce mucus which lines the inner walls of the intestines to protect them from being digested by proteolytic enzymes and also lubricates food as it moves through the lumen reducing any friction in the gut. The wall of the small intestines, just like in the oesophagus and stomach, is made up of circular and longitudinal muscles which contracts and relax antagonistically to facilitate peristalsis and mix food with juices and enzymes for rapid digestion. Walls of the small intestine have glands that secretes enzymes, for example maltase, sucrase, lactase, and peptidase which digest food into simple absorbable particles. Intestines internal wall epithelium have numerous villi with microvilli on their surfaces which further increase surface area for absorption of food. Microvilli have a thin epithelial layer providing a shorter diffusion distance for digested food. There is a presence of lacteal vessels in the small intestine into which fatty acids and glycerol are absorbed for transportation into the lymphatic system. What happens to the fatty acids and glycerol next? The intestines are highly vascularised which supply them with oxygen and also ensure faster absorption of digested steep products by maintaining a concentration gradient. Group Activity 5.2 Colon is the site for absorption
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of water and mineral salts and rectum is the site for temporary storage of undigested and indigestible materials. Did you know? Detergents claiming to remove oil and blood stains contain digestive enzymes like salivary amylase, pancreatic lipase and proteases like pepsin. Physical exercises are known to increase digestive systems movements and helps one get in shape too. Group Activity 5.1 In groups of four, role play the action of digestive enzymes and absorption of digested food. Digestive system of Ruminants (Polygastric digestion) Ruminants are herbivores and include animals like goats, sheep and cattle. However, camels are pseudo-ruminants. What do you observe in the Figure 5.10 below? Observe Figure 5.1 again and draw a comparison with Figure 5.9. Identify the differences in the digestive parts. Anus Large intestine Small intestine Rumen Mouth Oesophagus Reticulum Omasum Abomasum Fig. 5.10: Goat digestive system. 129 Observe the photographs below. What do you see? Fig. 5.11: The rumen and reticulum of ruminants. Which part of the ruminant are shown in the photographs? Why do ruminants need these parts seen in the photographs? The facts Ruminants are herbivorous mammals which are animals that feed exclusively on vegetation cellulose material that forms the cell wall. They lack incisors in the upper jaw, instead they have a hard pad against which grass is pressed and cut with incisors in the lower jaw. Incisors in the lower jaw are well developed with sharp chisel edge for cutting and tearing of grass and other plants. They have no canine teeth, instead they have a gap called diastema which helps to hold the regurgitated grass before pushing it to the premolars and molars for grinding. The molars and premolars have ridges/cusps in the grinding surfaces which slide over one another with the grass in between hence grinding into tiny particles. The enamel of the molars and premolars have large surface area for grinding food. The joints of the jawbones are loose allowing circular jaw motion in the horizontal plane ideal for grinding food. Their premolars and molars have open enamel in the crown allowing continuous growth of teeth throughout their life; hence reduces the incidence of wear and tear due to grinding. They have long and elaborate digestive systems for effective breakdown of indigested
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food. In Figure 5.10, you observe that ruminants have four chambered stomachs with rumen, where digestion of cellulose takes place due to the presence of bacteria and protozoa; that selects enzyme cellulase. In Figure 5.10, the food swallowed enters the rumen the largest chamber, where fermentation occurs. The fermenting food continues to the next chamber called the reticulum. The fermenting food is regurgitated to the mouth for grinding by the premolar and molar teeth. This is called chewing cud, which is physical digestion. The re-swallowing of the fine ground food directs the food 130 to the omasum where water is extracted and semi solids passed on to the abomasum, the true glandular stomach, like human stomach see Figure 5.10. The rest of digestion is similar to the human digestion. Did you know? Some cows will make between 40,000 to 60,000 jaw movements a day chewing cud. 3. Starting from the posterior end of the body, cut the body wall along the lateral side to the head using a sharp scalpel. 4. With the cut lateral side up, pin the specimen on the dissection board. 5. Flip open the dorsal part of the body wall to one side and the ventral part of the body wall to the opposite side. Loosen the body wall further by cutting at the anus and at the head. Digestive system of insects (locust) 6. Pin out the body wall to expose Practical Activity 5.3 In groups The locust is a relatively large insect to dissect. Requirements • Live locust or grasshopper or cockroach the internal organs. 7. Identify the structures and their functions referring to Figure 5.10 and any other resources available. 8. Make a large well-labelled diagram annotating it to the functions of each structure. • Sharp scalpel or razor blade or fine pair of scissors The facts • Dissection board or wax tray • Dissection pins or office pins • Hand lens • Sharp pencil and paper • Eraser Procedure Divide roles amongst the group members. 1. Obtain a mature locust from the school field and put it in an airtight jar containing chloroform. 2. Remove the locust from the jar and cut off the wings. In a locust, the mouth leads to a short oesophagus. Posterior to the oesophagus is a relatively large crop which stores food. At the
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posterior of the crop are gizzard and gastric caecae. Gastric caecae secrete digestive enzymes and provide a larger surface area for absorption while the gizzard is an active grinding organ using ridges of cuticle. The oesophagus, crop, gizzard and gastric caecae form the fore gut. 131 Oesophagus Crop Gizzard Stomach Ileum Colon Anus Rectum Intestine Pharynx Labrum Mandible Labium Salivary duct Salivary glands Malpighian tubules Gastric caecae Fig. 5.12: Locust’s digestive system. Posterior to gastric caeca is the midgut or stomach where digestion and absorption takes place. The Malpighian tubules are to the posterior of the midgut. They are organs of excretion extracting water from the faecal pellets. The pellets proceed to pass through the colon, rectum and out through the anus. Digestive system of fish Practical Activity 5.4 You are provided with the following items; • Whole Tilapia fish • Sharp fine scissors • Wax tray • Hand lens Procedure 2. Observe carefully to see that from the gill arches, the gill rakers, projects inwards. 3. Make a small cut by inserting a fine scalpel blade into the anus (vent) of the fish. 4. Extend the cut anteriorly along the fish’s belly towards the head. through and the cut Make between the pelvic fins. 5. Use the pair of scissors to cut anteriorly through the bones attached to the pelvic fins to expose the mouth cavity. 6. With the help of your teacher or the Internet, identify the digestive system of fish. Internet 1. Using the pair of scissors, cut out the operculum or gill cover to expose the gills beneath. Use this link: http://share.nanjingschool.com/sciences/files/2013/02/ fish-dissection-2e5c6ra.pdf 132 The facts The digestive system in fish is variant being adapted to the mode of feeding of the fish, either carnivorous and herbivorous fish. However, most fish have digestive systems that include a mouth, teeth, gill rakers, oesophagus, stomach, pylorus, pylorus caeca, pancreatic tissue area, liver, gall bladder, intestine and anus. The table below compares the digestive systems of two types of
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fish on the bases of feeding mode. Table 5.2: Summary on digestion in fish Digestive system part Carnivorous fish digestive Mouth Teeth Gill rakers Oesophagus system Large Pointed jaw and pharyngeal teeth Fine filters Mucus lubricated Stomach Pylorus Pylorus caeca Posterior to stomach Elastic muscular wall Control sphincter Enzyme secretion or absorption Herbivorous fish digestive system Small Pharyngeal teeth Course filters Mucus lubricated Thin wall Control sphincter Enzyme secretion or absorption Pancreatic tissue area Liver Exocrine /endocrine roles Exocrine /endocrine roles Secretes bile Secretes bile Protein digestion in human beings Practical Activity 5.5: Demonstrtion of the presence and action of enzymes in cells You are provided with the following items: • Suspension W (10% egg white) • NaOH solution • CuSO4 solution Procedure 1. Using the reagents provided, carry out food tests. In the table below, record the food test, the procedures, observations and conclusion. Food substance Procedure Observation Conclusion 2. Mention two enzymes that may be required to digest suspension W in the alimentary canal of a mammal. 3. (i) State the purpose of hydrochloric acid in the stomach. (ii) State the purpose of sodium hydrogen carbonate in the duodenum. 133 The facts in the Protein digestion begins mouth. Protein food is broken down mechanically by the teeth into tiny particles to increase surface area for subsequent enzymatic digestion. It is also mixed with saliva that contains mucus to lubricate it for easy swallowing. When food reaches the stomach, it stimulates the production of gastrin hormone that influences the production of gastric juice from gastric glands in the stomach walls. Gastric juice contains rennin, pepsin and hydrochloric acid. Rennin curdles milk increasing its surface area for digestion by pepsin. Hydrochloric acid promotes conversion of inactive pepsinogen into active pepsin, which then digests proteins into peptides. Hydrochloric acid also provides an acidic medium suitable for proper functioning of rennin (chymase) and pepsin. It also destroys pathogens contained in the food. The chyme then moves into the duodenum through sphincters. Presence of food in the duodenum stimulates production of secretin hormone from duodenal wall. Secretin hormone in turn stimulates liver cells to produce
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bile. It also stimulates the pancreas to produce pancreatic juice. Pancreatic juice contains trypsinogen which is converted into active trypsin. By the action of enterokinase, trypsin then digests polypeptides into dipeptides. The dipeptides are then digested into amino acids by peptidase produced in the ileum. Remember Spelling of rennin as renin refers to a hormone secreted into the blood by 134 cells lining the efferent glomerular vessels of the kidney. Renin reacts with angiotensin from the liver to stimulate adrenal gland to release aldosterone. Lipid digestion in human beings The facts Lipid digestion starts in the duodenum. Bile from the gall bladder is released and contains bile salts which breakdown fats to tiny fat droplets to increase the surface area for enzyme pancreatic lipase to digest. The process of breaking down of lipids by bile salts is called emulsification. Pancreatic lipase digests lipids into fatty acids and glycerol. The intestinal juice secreted by the intestinal wall glands contains intestinal lipase which breaks down the remaining lipids into fatty acids and glycerol. Food absorption and assimilation How does the process of food assimilation occur within the small intestine? The facts acids, fructose, Protein and simple sugars absorption: Amino galactose and glucose diffuse through the thin epithelial lining of the microvillus into blood capillaries and are transported into the liver via hepatic portal vein. Protein assimilation: The proteins in the body are used for synthesis of new cells, growth and repair of worn-out tissues some of the non-essential amino acids are used in protein synthesis. Excess amino acids are broken down (deaminated) into urea and carbon residue. Urea is eliminated from the body as urine while the carbon residue is used in the carbohydrate metabolism and either converted into the glycogen for storage in the liver or during food shortage converted into glucose and broken down during respiration to provide energy. Glucose assimilation: Excess glucose is converted to glycogen by action of insulin. Excess glucose is converted to fats and some glucose is used in cell respiration to provide energy. Physical and chemical digestion How does the chemical and physical digestion processes occur in the body? Practical Activity 5.6. The action of amylase on starch Requirements • Hot water bath • Four test tubes labelled A, B
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, C and D • 2% starch solution • Amylase solution Iodine solution • • Benedict’s solution • Measuring cylinder Procedure 1. Using the measuring cylinder, place 5 cm3 of 2% starch solution in each test tube. 2. Rinse the measuring cylinder then use it to add 2 cm3 amylase solution in each of tubes B and D then shake the test tubes to mix the contents and allow them to stand for 6 minutes. 3. After 6 minutes, add 3 drops of iodine solution to tubes A and B. Rinse the measuring cylinder then use it to add 2 cm3 of Benedict’s solution to tubes C and D then place the tubes in the hot water bath for 5 minutes. 4. Compare the final colours in the tubes and complete the table of results (Table 5.3). Table 5.3: Table of results Test Tube A B C D Test tube content 2% starch solution Reagent used Iodine 2% starch solution + amylase Iodine 2% starch solution + amylase Benedict’s 2% starch solution Benedict’s Observation Conclusion (a) What normally happens when iodine solution is added to starch? (b) Tube B contained starch solution at the beginning of the experiment. How do you explain the reaction with iodine at the end of the experiment? (c) What food substance is Benedict’s solution a test for? (d) Was this food substance present in tubes C or D at the beginning of the experiment? What evidence do you have to support your answer? 135 is (e) What evidence there to suggest that this food substance is present in tube C at the end of the experiment? (f) What chemical change could have taken place in tubes B and D after adding amylase, which would explain the results in these tubes after applying the iodine test and Benedict’s test? (g) What part could amylase have played in this chemical change? (h) Suggest a control to the experiment which would help to support your answers. The facts Digestion: In the mouth, protein food is broken down mechanically by the teeth into tiny particles to increase the surface area for subsequent enzymatic digestion. It is also mixed with saliva that contains mucus to lubricate it for easy swallowing. Digestion of starch in the mouth is partly mechanical or physical and partly chemical digestion. Mechanically, the chewing action of the teeth and the movement of the tongue breaks down the food into smaller
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particles. Chewing produces a greater surface area for the action of enzymes. The physical digestion of food is possible by mastication and churning of food particles to fine pieces and emulsification of lipids to smaller lipid droplets. Mastication, churning and emulsification increase the surface area of foods for the action of enzymes. 136 Large lipid droplet Sodium bicarbonate Tiny droplets of lipids Fig. 5.13: Emulsification of lipids. food The starch is broken down chemically by the action of salivary amylase which converts some of the starch present into maltose. Saliva also moistens and lubricates the food. The starch is then swallowed into the oesophagus where it moves down to the stomach by peristalsis. As the stomach muscles continue peristaltic agitation (churning), all the food types are physically broken down into smaller particles. Salivary amylase continues to digest starch until the gastric juice penetrates the softened food mass, denaturing the salivary amylase. When food reaches the stomach, it stimulates the production of gastrin hormone that influences the production the gastric of gastric glands in the stomach walls. Gastric juice contains rennin, pepsin and hydrochloric acid. Rennin curdles milk increasing its surface area for digestion by pepsin. Hydrochloric acid promotes conversion of inactive pepsinogen into active pepsin which then digest proteins into peptides. Hydrochloric acid also provides an acidic medium suitable for proper functioning of rennin (chymase) and pepsin. It also destroys pathogens contained in the food. from juice No enzymatic action takes place on carbohydrates when the food is in the stomach. However, the hydrochloric acid produced by the gastric gland starts the hydrolysis of sucrose to glucose and fructose or lactose to galactose and glucose or maltose to glucose. The food leaves the stomach through the pyloric sphincter and reaches the duodenum, the first part of the small intestine. Here, the food mixes with bile (to neutralise its acidity) and pancreatic juice which contains a starch digesting enzyme pancreatic amylase. Pancreatic amylase converts the starch to maltose. As the food moves to the ileum, it mixes the intestinal juice or succus entericus which contain several enzymes that complete the digestion of carbohydrates as follows:
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Maltase which hydrolyses or changes or converts maltose to glucose, Sucrose which hydrolyses sucrose to glucose and fructose, lactase which to glucose and hydrolyses galactose. These are then absorbed into the blood capillaries in villi. the then moves The chyme duodenum through sphincters. Presence of food in the duodenum stimulates production of secretin hormone from duodenal wall. Secretin hormone in turn stimulates liver cells to produce bile. It also stimulates the pancreas to lactose into produce pancreatic juice. Pancreatic juice contains trypsinogen which is converted into active trypsin. By the action of enterokinase, trypsin then digests polypeptides into dipeptides. The dipeptides are then digested into amino acids by peptidase produced in the ileum. Group Activity 5.3: Role play Role play digestion by enzymes and absorption. Different group members will have to play the part of (A) glucose molecules (initially joined together to make starch; (B) enzymes and (C) the wall of the intestine. Steps: 1. (A) all hold hands to represent a long chain starch molecule. 2. (A) release hands as enzymes (B) break down the chain into small glucose sub-units. 3. (A) Who are now separate glucose molecules pass through narrow spaces between other learners (C) – the wall of the intestine–as they are absorbed into the body. Functions of associate organs What are the functions of glands, and organs which aid digestion? 137 Group Activity 5.4 The liver, the pancreas and gall bladder all are important to the process of digestion. Suggest how important? In your class suggest to each other what would happen if any of them was surgically removed? Fig. 5.14: Accessory organs The facts As Group activity 5.3 may have pointed out to you the duodenum has associate glands and organs. These are: (i) Liver – secretes bile, stored in the gall bladder, which has bile salts that emulsify fats into tiny fat droplets to be chemically digested by pancreatic lipase. exocrine gland. As (ii) Pancreas – which is an endocrine and an endocrine gland, it secretes insulin and glucagon to the bloodstream to regulate amount of glucose in the blood. As an exocrine gland, it secretes
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pancreatic juice which contains sodium carbonate that neutralises acidic chyme from the stomach providing alkaline medium for pancreatic enzymes action, pancreatic amylase enzyme that digest starch into maltose, pancreatic lipase that digest fats or lipids into fatty acids and glycerol, and trypsin enzyme that digests proteins into peptides (ii) Brunner’s glands – they secrete an mucus-rich fluid of high pH in the duodenum to prevent corrosion by the acidic chyme. Sites of chemical digestion Where in the body do most chemical digestion take place? The facts sites and The chemical digestion substrate food are tabulated below (suggest the end products of chemical digestion by each of the enzymes). 138 Table 5.4: Summary of digestion sites, food substrates and enzymes involved Chemical Digestion Site Enzyme involved Suggest the end products Substrate Mouth Stomach Stomach Duodenum Duodenum Duodenum Ileum Ileum Ileum Ileum Starch Milk casein Salivary amylase Rennin Pepsin Starch Lipid Proteins Sucrose Maltose Lactose Peptides Protein Pancreatic amylase Pancreatic lipase Pancreatic trypsin Sucrase Maltase Lactase Aminopeptidase Muscles involved in digestion How do muscles move food through the digestive tract? The role muscles play during digestion in human beings include: • The cheek muscles are involved in the movement of cheeks sideways during chewing of food and therefore mixing the food. • The alimentary canal muscles contract and relax during peristalsis to move the food along as it is digested. • The cardiac sphincter muscles relax to allow passage of the food bolus into the stomach and contract to prevent food regurgitation during churning of food in the stomach. • The pyloric sphincter muscles contract to regulate exit of food from the stomach into the duodenum for hours until churning is complete when it relaxes to allow regulated passage of the liquid food chyme. • The thick and powerful circular and longitudinal muscles of the stomach wall contract and relax to churn food and in the process, break it into smaller particles. The result is chyme. 139 Check your progress 5a 1. (a) Given the digestive system would you label and suggest the function(s) of all the parts involved in digestion of food. (b) Create a table to summarise the main substances
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produced by digestion. The column headings should be titled: region of alimentary, digestive gland, digestive juice produced, enzymes in the juice, class of food acted upon and end substance produced. 2. Given an illustration of the digestive system in human beings, plus a ruler, pen and paper, how would you be able to label all parts and state function(s) of each named part. 3. Given an illustration of the digestive system in goats, a ruler, pen and paper, how will you be able to label all parts and state function(s) of each named part? 140 IHGFEDKLMNPQCJAB 4. Given an illustration of the digestive system in a locust, a ruler pen and paper, how would you be able to label all parts and state function(s) of each named part. 5. Given an illustration of the digestive system in tilapia, a ruler pen and paper, how would you be able to label all parts and state function(s) of each named part? 6. Given the digestive system in human beings, cows, bees and Nile perch, how would you be able to compare them. 7. Given the following pairs of terms: Ingestion and egestion, digestion indigestible, absorption and assimilation, and how would you be able to distinguish them? and 8. Digestion occurs in human beings, ruminants, insects and fish. Why do you need to digest food? 5.2 Circulatory system How are you today? Are you feeling well? How do you know you are well? Group Activity 5.5 1. Observe the picture below. What do you see? Fig. 5.15: Taking pulse rate. Fig. 5.16: Stethoscope 2. Do you remember the instrument in Figure 5.16 being used on you somewhere? 3. Why was it being used on you? 4. Form groups of four. 5. Using a stethoscope listen to each other’s hearts. Record in your notebooks the number of heartbeats per minute and the heart sounds you hear. (If a stethoscope is not available then use the method in figure 5.15) In turns, one learner will be the doctor while another learner will be the patient, the third learner the nurse recording will be what the doctor is observing (hearing), and the fourth learner is the time keeper and patient attendant making sure the patient is comfortable during the doctor�
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�s examination. 6. 7. After the first reading change roles until each learner has had the chance to be a doctor, a nurse, a patient and a patient attendant. NB: Respect the patient’s rights as the doctor and do not touch the patient inappropriately. 141 8. Why do doctors listen to your heartbeat as they examine you at the health facility? 9. What does this information tell them about your health? 10. Touch your left side of the chest. Do you feel the heartbeat? How does that heartbeat transfer to your neck? Single and double circulation The facts studied in Italy, his teacher taught him about dissections and when he returned to England he continued to dissect animals and refused to follow what the textbooks of those days said about the animal circulatory system. He would later publish that blood is pumped by the heart to arteries and is circulated around the body and returns to the heart via the veins. Work to do Further reading You are welcome to read more on this amazing human being by visiting this website link: https:// www.famousscientists.org/williamharvey/ reading, design an the After illustration summarise your to understanding of the discoveries of the functioning of the heart and blood arteries. Fig. 5.17a: William Harvey The facts rapidly around Circulatory system is a blood transport system moving blood cells and blood the body plasma while linking various organ systems. This is important to all multicellular organisms because they have a small surface area to volume ratio to control water loss, and internal organs are far from the organism’s body surface. A circulatory system has the following components: blood as the circulating fluid, heart as the pump, blood vessels as the connecting tubes, and valves to ensure one direction of blood flow. Fig. 5.17b: Single and double circulation William Harvey was the first person to accurately document the functioning of the heart and the blood vessels. While he 142 Types of circulatory systems include; • Open circulatory system found in arthropods and molluscs. The heart pumps blood or haemolymph to a body cavity called haemocoel, then the blood or haemolymph returns via collecting blood vessels. Heart Hemolymph Fig. 5.18: Open circulatory system. • Closed circulatory system found in chordates like birds, fish and mammals. The heart pumps blood to the body via continuous blood vessels and cells. That are not in direct contact with the blood. The blood pressure is higher than in open
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circulatory system and ultrafiltration at the body tissues forms tissue fluid. Table 5.5: Comparison of open circulatory system and closed circulatory system Open circulatory system Blood is pumped into body cavities Closed circulatory system Blood vessels contain the blood throughout Blood flows at lower pressure Blood flow is at higher pressure Animals have slow metabolism Animals have faster metabolism Suitable for all sizes of animals Suitable for animals with a larger surface area to volume ratio Types of closed circulatory systems include: • Single circulatory system as seen in fish. The heart pumps the blood to gills via the afferent branchial arteries then the gill capillaries and efferent branchial arteries transport blood to dorsal aorta. The dorsal aorta branches to supply blood to body organs. The blood leaving the organs is at low pressure and collects in sinuses (large blood spaces) from which the heart can refill. This is a single circulatory system because the blood passes through the heart once to complete a cycle. 143 Respiratory capillaries Atrium Systematic capillaries Body Operculum Heart Sinus venosus Ventricle Fig. 5.19: Fish have single circulatory system. • Double circulatory system as seen in amphibians, reptiles, birds and mammals. The heart pumps the blood to the lungs and back to the heart (pulmonary circuit), then pumps the same blood to the rest of the body and back to the heart (systemic circuit) therefore it takes two blood passes to complete a cycle, hence double circulatory system. Lung capillaries Pulmonary circuit A V A V Right Left Systematic circuit Systematic capillaries Fig. 5.20: Birds and mammals have double circulatory system. 144 Blood circulation in humans and birds Group Activity 5.6 In collaboration with your classmates, form groups of six. Study and evaluate the diagram below then do the task that follows: Fig. 5.21: Human and bird circulatory system diagram. Your task today is to design a game to assist you understand how the blood circulation in birds and human beings work. Student Task: using available materials 1 2 3 Lung capillaries: receive deoxygenated blood from pulmonary artery and passes it on to the pulmonary vein as oxygenated blood. Go to the left atrium. Left atrium: receives oxygenated blood from pulmonary vein and pumps it through bicuspid valve to the left ventricle. Go to the left ventricle. Left ventricle: receives oxygen
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ated blood from the left atrium and pumps it through aortic semilunar valve to the aorta, then arteries and rest of the body. Go to the systemic capillaries. 145 VenulesVenulesArteriolesAortaArteryArteryArteriolesPulmonary arteryPulmonary veinVeinRight heartLeft heartVeinLUNGSLUNGSTissue capillariesTissue capillariesArterial circulationVenous circulation 4 5 6 Systemic capillaries: receive oxygenated blood from the artery system and pass deoxygenated blood on to the veins, then vena cava to right atrium. Go to the right atrium. Right atrium: receives deoxygenated blood from the vena cava and pumps it through tricuspid valve to right ventricle. Go to right ventricle. Right ventricle: receives deoxygenated blood from the right atrium and pumps it via pulmonary semilunar valve and pulmonary vein to the lungs. Go to the lungs. After designing and writing, post them on the wall at random. Using a small tennis ball, hit at any card at random read, copy into your notebook and then follow the instructions given on the particular card. At the next card read, copy and obey instructions then the next until you are back to the first card you hit with the ball. • Read what you have copied at each card. • What do you observe? • Whose path of movement did you trace? • Ask the next member of the group to try a different throw of the ball on another card and repeat the process. Is the pattern the same? • Did you know? Ancient Egyptians believed the heart, rather than the brain, was the source of emotions, wisdom and memory. The facts Blood circulation is needed to distribute dissolved nutrients, heat, metabolic waste products and hormones to the cells of the body. Muscular contractions of the heart pump the blood around the body of birds and human beings. Blood from the veins is received in the heart atria (singular: atrium) also called auricles. 146 Right pulmonary artery Right pulmonary vein Aorta Left pulmonary artery Left pulmonary vein Fig. 5.22: Diagram of the human/bird heart. Deoxygenated blood from the vena cava (largest vein) is received in the right atrium at the same time is received from the pulmonary vein in the left atrium. When the
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left and the right atrium are full of blood the atrium contracts to pump blood past the cuspid valves, which are two: The left cuspid valves are called the bicuspid valves while the right cuspid valves are called the tricuspid valves. The contraction of the atria is simultaneous and is self-generated by the pacemaker (sino-atria node, SAN). The atria contraction pumps blood into the ventricles and the two ventricles fill up with blood as they relax. When full of blood, the cuspid valves close and both ventricles contract. The left ventricle pumps blood past the aortic semilunar valves to the aorta onwards to the other arteries, while the right ventricle pumps blood past the pulmonary semilunar valves into the pulmonary artery onwards to the lungs. The blood from the lungs will return to the heart as oxygenated blood with lower carbon (IV) oxide content via the pulmonary vein into the left atrium. The blood from the aorta will be conveyed to the arteries then arterioles then capillaries (only located in the tissues or organs) then venules and veins leading to the vena cava. The vena cava will deliver the blood to the heart right atrium of the heeart. 147 Diastole Systole Fig. 5.23: Cardiac cycle, blood vessels and heart. Did you know? There are two main sounds (“lub” “dub”) made by your heart and they are the sounds of the cuspid valves and semilunar valves closing. When the cuspid valves close they make a “lub” sound and when the semilunar valves close, they make a “dub” sound. The stethoscope is used to listen to these sounds. Why would this be important to your doctor? Remember William Harvey What made him great? Is it being King Charles’ doctor? Is it his discovery of how blood flows? (a) What do you observe in the part labelled K? (b) Where in the body of a goat do you think the specimens K,M and N were obtained from? (c) What do you observe in the part labelled N? Group Activity 5.7 (d) What do you observe in the part Look at the photograph and the parts labelled M, N and K. Answer
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the following questions. labelled M? (e) Explain how parts K and M, in terms of their functions, are related. (f) What do you think makes K function as well as it does? 148 The facts Structural adaptations of the mammalian heart to its function The heart has valves namely atrioventricular valves (cuspid valves) and the semilunar valves which when opened allow blood to flow in one direction only; and when closed prevent backflow of blood. Position of aortic valve in heart Normal trscupid aortic valve Biscupid aortic valve Fig. 5.24 (i): Heart valves Valves have non-elastic chordae tendineae which prevent the atrioventricular valves from turning inside out into auricles during ventricular systole. Heart has thick muscular walls which contract to pump blood; and ensure its continuous flow. Heart has cardiac muscles, which are myogenic; and contract and relax without fatigue. Heart has sino atrial (SA) node and atrioventricular (AV) node which initiate cardiac muscle impulses and hence stimulate the contraction of the atria and ventricles respectively. Aortic semilunar valve Tricuspid valve Bicuspid valve Pulmonary semilunar valve 149 Fig. 5.24 (ii): Four heart valves. Heart is served by vagus and sympathetic nerves which regulate the rate of the heart beat depending on body’s physiological requirements. Cardiac muscles are served by coronary arteries, blood vessels, to supply oxygen and nutrients required by heart muscle cells to respire and by coronary vein which transports away carbon (IV) oxide and metabolic wastes. Heart has specialised interconnected cardiac Pürkinje fibres, which spread the wave of excitation throughout the heart muscles. The heart has four chambers, which hold blood briefly before it is pumped to the rest of the body and the lungs. Heart septum separates oxygenated blood on the left side of the heart from the deoxygenated blood on the right side increasing the efficiency of the heart as a double pump. Vena cava and pulmonary vein transport blood to the heart auricles from the rest of the body and lungs respectively. The pulmonary artery and the aorta transport blood from the heart ventricles to the lungs and the rest of the body respectively. The entire heart is enclosed by a tough double-layered protective sac, pericardium, which prevents the heart from being overstretched
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as it pumps blood. The pericardium secretes pericardial fluid, which lubricates its interior and reduces friction between the pericardial membranes as the heart moves within the inner membrane. The deposit of spongy fatty layer on the pericardium mechanically protects and cushions the heart. Work to do • Read the section about the adaptations of the heart to its function. • Create a table with three columns titled; structure, modification and function. • Complete the table by summarising what you understood after reading the section. Group Activity 5.8 1. Observe Figure 5.25(ii). What do you see? 2. Suggest what you think the red arrows represent. 3. Suggest what you think the blue arrows represent 150 Arteriole Venule b. capillary Valve Endometrium Smooth muscles Connective tissue a. Artery c. Vein Fig. 5.25 (i): Diagram of the blood vessels. Open your notebook and after reading the facts section label and write the function of each of the parts shown in Figure 5.21. • Veins which transport blood towards the heart and have the widest lumen (internal diameter) with semilunar valves preventing backflow of blood. The facts There are three main types of blood vessels: • Arteries which transport blood away from the heart. The largest artery is the aorta and the smallest is the arteriole. • Capillaries which transport blood from arterioles to venules. They are the smallest blood vessels, their walls are one cell thick and they offer the greatest resistance to blood flow. Capillaries are the sites of ultrafiltration and site of tissue fluid formation. vein artery capillaries Fig. 5.25(ii): Arteries, veins and capillaries. Do you remember William Harvey story? What did he say about the blood vessels? 151 Table 5.7: Structural differences between arteries and veins Arteries Have a small lumen Veins Have large lumen Have no valves except at the base of major arteries Have semilunar valves Have thick muscular walls which are elastic Have thin walls which are less elastic Located deeper away from the body surface Located nearer to the skin • Arteries have a high blood pressure compared to veins. • Arteries have a narrower lumen, which maintains high pressure while veins have a wider lumen that reduces pressure. • Blood is pumped directly into the arteries at high pressure by the heart. • Blood
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pressure in the veins is reduced by capillary resistance before it enters the veins. Did you know? A red blood cell’s diameter is slightly smaller than the internal diameter of the blood capillaries, therefore, they form a single-file line to fit through the blood capillaries in the body. Table 5.6: Functional differences between arteries and veins Arteries Veins Transport blood away from the heart Convey oxygenated blood except pulmonary artery Convey blood rich in nutrients Convey blood low in nitrogenous waste materials Blood is at high pressure Transport blood towards the heart except hepatic portal vein which transports blood from the intestines to the liver Convey deoxygenated blood except pulmonary vein Convey blood low in nutrient content except the hepatic portal vein and vena cava Convey blood high in nitrogenous waste materials except renal vein and vena cava Blood at low pressure Blood flow is in pulses Blood flow is smooth Have thick muscular elastic walls. Have a narrow lumen. Are located deep in the body. Walls are thin, less muscular and inelastic. Have a wider lumen. Are located nearer the skin. 152 Role of hormones in regulation of blood pressure Group Activity 5.9 • Observe Figure 5.26. What do you see? Fig. 5.26: A Patient being examined by a doctor. • Research in the library or • Internet how to read the blood pressure. If the patient was a healthy person, what readings do you suggest the doctor will make? • Explain the reading you have • suggested. If you were the patient, how would you influence the readings? The facts The blood pressure may increase or decrease if there are changes in the following: • The heartbeat rate increases, that increasing the volume of blood pumped to the artery per minute hence increasing blood pressure in the arteries. • Vasoconstriction and vasodilation of arteries and arterioles hence increase and decrease of blood pressure respectively. • Change in blood viscosity too would vary the blood pressure. The medulla oblongata has a cardiovascular centre responsible for controlling blood pressure by regulating the heartbeat rate and the vasoconstriction or vasodilation of blood arterioles. The following hormones influence the blood pressure regulation: • By controlling the blood volume, Renin hormone released from the kidney regulates blood pressure through Angiotensin II which in turn influence the action of aldosterone. • Antidiuretic hormone also increases blood pressure by causing more water retention by the kidney. • The at
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ria of the heart secrete a hormone called atrial natriuretic peptide responsible for lowering blood pressure through vasodilation and increase water loss by the kidney. Flight hormones released by the adrenal gland increase blood pressure too by increasing vasoconstriction and pulse rate. • Role of the heart in blood flow How does the heart regulate the rate of blood flow within the body of organisms? 153 The facts impulse within the ventricular muscle. A human female heart beats about 77 times per minute while a male heart beats about 70 times per minute. Every heatbeat pumps about 140 cm3 of blood out of the heart, therefore, in a day it pumps about 7,000 litres of blood around the circulatory system. Group Activity 5.10 How many beats does your heart make in a day? How would you increase the number of heartbeats your heart is making? How many beats does an average human heart make in a day? How many beats does an average human heart make in a lifetime? The facts The heartbeat rhythm is maintained by the pacemaker (also called the sino atrial node). The pacemaker has spontaneously active cells, that is they are myogenic cells and generate an impulse which is spread around the heart muscle–to the atria muscle first causing the contraction of the atria, then to the ventricle muscle via the heart conducting systems. The impulses are prevented from spreading directly to the ventricles by a fibrous layer between the atria and ventricles therefore, the heart conducting system of atrioventricular node and Bundle of His carry the impulse to the base of ventricular muscle at extremely high speed. From the base of the ventricular muscle the Pürkinje fibres transmit the 154 SA node Fig. 5.27: Coordination of a heartbeat. Group discussion In your discussion group, discuss: If you were the one designing your heart, why would you design it for the contractions to be coordinated as described above? Individual Activity 5.15 Draw Figure 5.27 in your notebook. Then reread the passage before the figure and then label the parts mentioned in the passage. The facts The contraction of the ventricles pumps blood into the pulmonary artery and aorta. The left ventricle pumps blood a longer distance, therefore, has a thicker wall to generate more pumping power and pressure. Did you know? Why your heartbeat feels like it is on the left side of your chest yet it is on the central position but slightly to the left?
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Because the left ventricle makes more powerful contractions than the right side. Hormones and heart rate the Your heartbeat speed may be increased autonomic or decreased by nervous system. There are two types of autonomic nervous systems, namely the sympathetic nervous system and the parasympathetic nervous system. The sympathetic system secretes hormones epinephrine (also called adrenaline) and norepinephrine to increase the heartbeat speed. After which the parasympathetic nervous system secretes hormone acetylcholine to decrease the heartbeat rate. Adrenal glands secrete the hormone adrenaline when you are afraid or angry causing an increase in heartbeat rate hence blood pressure and rate of use of glucose in the muscles. These hormones stimulate the pacemaker to release impulses at a faster rate hence increase heart muscle contractions. Blood components and functions Plasma (55%) White blood cells + platelets ( <1%) Red blood cells (45%) Fig. 5.28: Components of blood. Blood components Individual Activity Study the diagrams in Figure 5.28 showing the blood components, then draw a table showing a component and its function. 155 Fig. 5.29: Blood components mind map. The facts The red blood cells contain haemoglobin which has a high affinity for oxygen and combines with oxygen in areas of high oxygen tension to form oxyhaemoglobin. Haemoglobin also reacts with carbon (IV) oxide forming carbaminohaemoglobin. The red blood cell is biconcave in shape to increase its surface area for diffusion of oxygen and carbon (IV) oxide in and out of the cell. The mature red blood cell lacks a nucleus and other cell organelles to provide adequate spaces for packing haemoglobin involved in transport of the oxygen and carbon(IV) oxide. Inside the red blood cells the rate of reaction between water and carbon (IV) oxide is increased by carbonic anhydrase to form carbonic acid. The haemoglobin reacts with hydrogen ions from the dissociation of carbonic acid therefore buffering the plasma pH. The red blood cells are the most numerous 156 blood cells to ensure efficient transport of oxygen and carbon (IV) oxide to the respiring tissues and from the tissues respectively. White blood cells fight infections in a number of ways, namely neutrophils and monocytes phagocytise (ingest) pathogens; eosinophils phagocytise antigen-antibody complexes and allergens; basophils release histamine which promotes blood flow to injured tissues and lymphocytes are involved
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