KSSM 2019 Form 4 Biology Part 2 PDF

9 CHAPTER Nutrition and the Human Digestive System 3D food printer Do You Know... Can food be designed to meet the nutritional needs of humans? What are the str uctural components of the human digestive system? How is food dig ested and absorbed? How does food assimilation occur? How does defaec ati...

9 CHAPTER Nutrition and the Human Digestive System 3D food printer Do You Know... Can food be designed to meet the nutritional needs of humans? What are the str uctural components of the human digestive system? How is food dig ested and absorbed? How does food assimilation occur? How does defaec ation occur? What is a balance d diet? 142 BioT4(NC)-B9-EN New 7th.indd 142 1/9/2020 12:10:03 PM 9.2 Digestion 9.2.1 Describe the types of digestion: physical digestion chemical digestion 9.2.2 Analyse the process and products of carbohydrate digestion in the mouth. 9.2.3 Analyse the process and products of protein digestion in the stomach. 9.2.4 Describe digestions of carbohydrates, proteins and lipids in the small intestine. 9.2.5 Conduct experiments to study digestions of starch, proteins and lipids in food samples. 9.3 Absorption 9.3.1 Identify the structure of a villus in the ileum. 9.3.2 Communicate about the adaptations of ileum and villus in the absorption of digested food. 9.4 Assimilation 9.4.1 Describe the roles of the circulatory system in the assimilation of digested food. 9.4.2 Discuss the functions of liver in the assimilation of digested food: metabolism of digested food (carbohydrates and proteins) storage of nutrients detoxification 9.5 Defaecation 9.5.1 Explain the functions of the large intestine: absorption of water and vitamins formation of faeces 9.6 Balanced Diet 9.6.1 Conduct an experiment to study the energy values in food samples. 9.6.2 Conduct an experiment to determine the contents of vitamin C in fruit or vegetable juices. 9.6.3 Justify the modification of diets for individuals who: experience obesity experience a specific disease – diabetes mellitus – cardiovascular – cancer 9.7 Health Issues Related to Digestive System and Eating Habits 9.7.1 Predict the effects of modifying digestive organs on human health. 9.7.2 Outline health issues related to defaecation. 9.7.3 Correlate health issues that are related to eating habits. CHAPTER 9 9.1 Digestive System 9.1.1 Identify structures of the human digestive system. 143 BioT4(NC)-B9-EN New 7th.indd 143 1/9/2020 12:10:03 PM 9.1 9.2 salivary gland tongue Digestive System Structure of the human digestive system The human digestive system is made up of a long and muscular alimentary canal that starts from the mouth to the anus (Figure 9.1). The parts of the alimentary canal include the mouth, oesophagus, stomach, small intestine, large intestine and anus. The other organs in the digestive system are liver, gallbladder and pancreas. Salivary, gastric and intestinal glands secrete digestive juices into the alimentary canal. Digestion Types of digestion Digestion is the process that breaks down large and complex pieces of food into smaller and simple pieces that can be dissolved for easy absorption. Digestion is made up of two parts, that is, physical digestion and chemical digestion. mouth pharynx oesophagus bile duct Chemical digestion The mechanical breakdown of food to form small particles The decomposition process of complex molecules into simple molecules Involves chewing and peristalsis Involves enzymes reaction Digestion of carbohydrates in the mouth liver gallbladder Physical digestion stomach The digestive process begins in the mouth. The presence of food in the mouth stimulates the secretion of saliva from the salivary glands. pancreas small intestine large intestine appendix AR rectum anus 144 BioT4(NC)-B9-EN New 7th.indd 144 FIGURE 9.1 Human digestive system 9.1.1 9.2.1 9.2.2 1/9/2020 12:10:05 PM Saliva contains salivary amylase that hydrolyses starch to maltose. The pH of the saliva ranges between 6.5–7.5, which is suitable for salivary amylase to act at its optimum. Starch + water Salivary amylase maltose Saliva helps food to form bolus and makes it easier to be swallowed. When swallowing, the epiglottis will close the trachea opening to prevent food from entering the trachea. In the oesophagus, the food bolus is moved by peristalsis. the muscular walls of the Peristalsis is the rhythmic contraction and relaxation oesophagus relax of muscles along the alimentary canal. Peristalsis pushes the bolus through the oesophagus until it enters the stomach (Figure 9.2). Digestion of protein in the stomach The surface of the stomach wall is lined with epithelial cells that have undergone adaptations in structure and function to form gastric glands (Figure 9.3). These epithelial cells are chief cells, parietal cells and mucous cells. Chief cells secrete pepsinogen. Parietal cells secrete hydrochloric acid. Mucous cells secrete mucus. the muscular walls of the oesophagus contract oesophagus bolus FIGURE 9.2 Peristalsis Brainstorm! Chew slowly a small piece of bread. Observe the taste when you first started chewing and after a few minutes of chewing. Is there any difference in the taste of the bread? gastric gland oesophagus CHAPTER 9 stomach epithelium duodenum sphincter FIGURE 9.3 Structure of stomach and gastric gland tissues mukosa Pepsinogen is an inactive enzyme that is activated by hydrochloric acid to become pepsin. Pepsin then hydrolyses proteins into polypeptides. Protein + water submukosa 9.2.3 BioT4(NC)-B9-EN New 7th.indd 145 pepsin mucous cells parietal cells chief cells polypeptides 145 1/9/2020 12:10:08 PM The functions of hydrochloric acid are to: (a) prepare a medium with a suitable pH (pH 1.5–2.0) for pepsin to act (b) stop the enzymatic action of salivary amylase (c) kill bacteria in food The function of mucus is to protect the stomach wall from the reaction of hydrochloric acid and digestive enzymes. The food in the stomach is mixed with gastric juice made up of hydrochloric acid and pepsin. Food is churned by the peristaltic action of the stomach wall muscles for a few hours. The contents in the stomach finally change to a semifluid called chyme. Chyme enters the duodenum slowly when the sphincter muscle relaxes. Digestions of carbohydrates, proteins and lipids in the small intestine The small intestine consists of duodenum, jejunum and ileum. Duodenum is the first part of the small intestine which receives chyme from the stomach. Duodenum also receives bile produced by the liver and pancreatic juice secreted by the pancreas (Figure 9.4). liver PANCREAS The pancreas secretes pancreatic amylase, trypsin and lipase into the duodenum through the pancreatic duct. LIVER Produces bile The gallbladder stores bile. The bile flows into the duodenum through the bile duct. Functions of bile – neutralise the acidic chyme – prepare an alkali condition (pH 7.6–8.6) for enzyme action in the duodenum – emulsify lipids by breaking down lipids into tiny droplets to increase surface area for lipase activity. 146 BioT4(NC)-B9-EN New 7th.indd 146 stomach bile duct chyme gallbladder pancreas duodenum pancreatic duct FIGURE 9.4 Components that are involved in digestion that take place in the small intestine DUODENUM Pancreatic amylase hydrolyses starch to maltose pancreatic amylase Starch + water maltose Trypsin hydrolyses polypeptides into shorter peptides. trypsin Polypeptide + water peptides Lipase hydrolyses lipids into fatty acids and glycerols. Lipid + water lipase fatty acid and glycerol 9.2.4 1/9/2020 12:10:09 PM Glands on the ileum wall secrete mucus and intestinal juice that contains maltase, sucrase, lactase, lipase and erepsin. The alkali medium in the ileum allows enzymes to act at its optimum. CARBOHYDRATE DIGESTION Maltase hydrolyses maltose into glucose. Maltose + water maltase glucose Sucrase hydrolyses sucrose into glucose and fructose. sucrase Sucrose + water glucose + fructose Lactase hydrolyses lactose into glucose and galactose. lactase Lactose + water glucose + galactose Lipase hydrolyses lipids into fatty acids and glycerols. lipase Fatty acids Lipid + glycerol + water PROTEIN DIGESTION Erepsin hydrolyses peptides into amino acids. Peptides erepsin amino + water acids Across the fields Chemical digestion involves enzymecatalysed hydrolysis reaction. For example, an enzyme is needed in the decomposition of starch into glucose. Studying the digestion of starch in a food sample Problem statement Hypothesis Amylase hydrolyses starch to a reducing sugar. Experiment thermometer thermometer thermometer A B AA BB What is the effect of amylase on starch? A B Variables Video: Processes of digestion, absorption and defaecation (Accessed on 21 August 2019) CHAPTER 9 tivitcA Activity 1.2sei9.1 ICT 9.1 LIPID DIGESTION 3 ml starch 3 ml of of 1%1% starch suspension + 3 ml suspension + 3 ml of 0.5% amylase of 0.5% amylase solution solution Manipulated: Presence of amylase Responding: Presence of reducing sugar Fixed: Temperature of water bath at 37˚C, concentration of starch suspension and volume of mixture 3 ml of 1% starch 3 ml of 1% starch suspension + 3 ml suspension + 3 ml of distilled water of distilled water water bath water bath (37 °C) (37 °C) bath water (37 °C) Materials 0.5% amylase solution, 1% starch suspension, iodine solution, Benedict’s solution and distilled water Apparatus Tripod stand, Bunsen burner, wire gauze, 500 ml beaker, test tube holder, thermometer, stopwatch, test tube, dropper, glass rod and measuring cylinder 9.2.5 BioT4(NC)-B9-EN New 7th.indd 147 147 1/9/2020 12:10:09 PM Procedure 1 Label 2 test tubes as A and B. 2 Add 3 ml of 1% starch suspension to each test tube. 3 Fill test tube A with 3 ml of 0.5% amylase solution and test tube B with 3 ml of distilled water. 4 Soak both test tubes in a water bath with a temperature of 37 °C for 10 minutes. 5 After 10 minutes, remove 2 ml of the solution from test tube A and put it into a different test tube. Add 3 drops of Benedict’s solution to that test tube and heat the test tube in a boiling water bath for 1 minute. Record the colour of the content. 6 Add 2 drops of iodine solution to the remainder of test tube A. Observe and record the colour of the contents. 7 Repeat steps 5 and 6 for test tube B. Results Test tube Contents A 1% starch suspension + 0.5% amylase solution B 1% starch suspension + distilled water Iodine test Benedict’s test Discussion 1 Explain the reaction that occurs in test tube A. 2 What is the purpose of preparing test tube B? Conclusion Is the hypothesis accepted? Suggest a suitable conclusion for this experiment. Activity 9.2 Studying digestion of protein in a food sample Experiment Problem statement What is the effect of pepsin on protein? Hypothesis Pepsin hydrolyses proteins in the albumen suspension into polypeptides. Variables Manipulated: Presence of pepsin Responding: Clarity or turbidity of mixture after 20 minutes. Fixed: Temperature at 37˚C, concentration of pepsin solution and dilute hydrochloric acid Materials Albumen suspension (egg white), 1% pepsin solution, distilled water and 0.1 M dilute hydrochloric acid Apparatus Test tube, measuring cylinder, 500 ml beaker, water bath at 37 °C, dropper, thermometer and stopwatch. 148 9.2.5 BioT4(NC)-B9-EN New 7th.indd 148 1/9/2020 12:10:09 PM Procedure 1 Prepare an apparatus set-up as follows. Test tube A: 5 ml of albumen suspension + 1 ml of 0.1 M hydrochloric acid + 1 ml 1% pepsin solution Test tube B: B + 1 ml of 0.1 M hydrochloric 5 ml of albumenAsuspension acid + 1 ml distilled water thermometer A B 2 Soak all test tubes in a water bath at 37 °C. 3 Observe the condition of mixtures in test tubes A and B at the beginning of the experiment and after 20 minutes. Results water bath (37 °C) Clarity or turbidity Test tube 0 minute 20 minute A B Discussion 1 Explain the results achieved in test tube A and B. 2 What is the purpose of adding hydrochloric acid into each test tube? Conclusion CHAPTER 9 Is the hypothesis accepted? Suggest a suitable conclusion for this experiment. Activity 9.3 Studying the digestion of lipids in a food sample Experiment Problem statement What is the effect of lipase on lipid? Hypothesis Lipase hydrolyses lipids into fatty acids and glycerols. Variables Manipulated: Presence of lipase Responding: Time taken for the phenolphthalein indicator to turn from pink to colourless Fixed: Temperature at 37°C, volume of cooking oil and combined volume Materials Cooking oil, 0.2 M sodium carbonate solution, dishwashing liquid, phenolphthalein indicator, distilled water and lipase 9.2.5 BioT4(NC)-B9-EN New 7th.indd 149 149 1/9/2020 12:10:09 PM Apparatus Two test tubes, test tube rack, water bath at 37 °C, 5 ml and 1 ml syringes, dropper, stopper and stopwatch thermometer Procedure A label them B 1 Prepare two test tubes and as A and B. A B 2 Fill each test tube A and B with the following: 2 ml of cooking oil 1 ml of 0.2 M sodium carbonate solution 1 ml of dishwashing liquid 3 Close both test tubes with stoppers. Shake both test tubes vigorously after adding the dishwashing liquid. water bath (37 °C) 4 Add 3 drops of phenolphthalein indicator to each test tube and shake the test tube. 5 Add 1 ml of lipase into test tube A and 1 ml of distilled water into test tube B. 6 Soak both test tubes in a water bath at 37°C. 7 Record the time taken for the phenolphthalein indicator to turn from pink to colourless. Results Test tube Contents A 1 ml of lipase B 1 ml of distilled water Time taken for the phenolphthalein indicator to turn from pink to colourless (minute) Discussion 1 Why is a phenolphthalein indicator used in this experiment? 2 What is the purpose of adding dishwashing liquid into each test tube? 3 Explain the reaction that happens in test tube A. 4 Explain the results obtained in test tube B. Conclusion Is the hypothesis accepted? State the suitable conclusion for this experiment. Formative Practice 9.1 1 Explain the importance of the digestion process for humans. 2 Name the structures in the alimentary canal that are involved in food digestion. 4 The small intestine secretes a few types of enzymes to complete the digestion process. Explain how these enzymes complete the digestion process. 3 Name the main cells in the gastric glands and explain the functions of these cells. 150 BioT4(NC)-B9-EN New 7th.indd 150 9.2.5 1/9/2020 12:10:10 PM 9.3 Absorption The adaptations of ileum and villus in the absorption of digested food Simple molecules produced from the digested food are absorbed in the ileum of the small intestine. ILEUM The long ileum is adapted to absorb nutrients because its internal layer is folded and covered by tiny projections called villi (singular: villus) (Figure 9.5). ileum cross section of a small intestine villus VILLUS (PLURAL: VILLI) Villus has the following adaptations to absorb nutrients (Figure 9.5): The epithelial layer of the villus is one cell thick. This helps accelerate nutrient absorption. Goblet cells secrete mucus to aid digestion. The network of blood capillaries helps to transport digestive products to the whole body. Lacteal carries droplets of fatty acids and glycerol. The intestinal glands secrete intestinal juices that have digestive enzymes. epithelial cells blood capillaries CHAPTER 9 lacteal lymph vessel nucleus microvillus basement membrane MICROVILLUS On the surface of the villus epithelium, there are many tiny projections called microvillus. Microvillus provides a large surface area to increase the rate of nutrient absorption (Figure 9.5). 9.3.1 9.3.2 BioT4(NC)-B9-EN New 7th.indd 151 mucus goblet cells FIGURE 9.5 Adaptations of ileum and villi to absorb digested food. 151 1/9/2020 12:10:14 PM Absorption of digested food is summarised in Figure 9.6 and Table 9.1. Petunjuk: Glukosa Indicator: ICT 9.2 Asid amino Asid lemak Glucose Video: View inside the small intestine (Accessed on 21 August 2019) Giserol lacteal Lakteal Amino acids Titisan halus lipid FattyGalaktosa acids Fruktosa Glycerol lacteal Millennial Career Millennial Career blood capillaries Kapilari darah Lipid droplets A gastroenterologist is a medical specialist who specialises in the human digestive system. Galactose Fructose FIGURE 9.6 Absorption of digested food TABLE 9.1 Method of food absorption in the ileum blood capillaries Activity Zone Gather information about the absorption of alcohol and drugs. Digested food Fructose Glucose and galactose Amino acids Vitamins B and C 152 BioT4(NC)-B9-EN New 7th.indd 152 Epithelial cells into blood capillaries Active transport Active transport Absorbed with water Fatty acids and glycerols recombine through the condensation process to form tiny droplets of lipids in the epithelial cells Simple diffusion Epithelial cells into lacteal Simple diffusion 9.2 2 Name the structure in the villus involved in the transporting of the following nutrients: (b) vitamins A and E Facilitated diffusion Osmosis 1 Name the main structures for the absorption of digested food. (a) amino acids Methods of absorption Water Vitamins A, D, E, K dissolve in the lipid Formative Practice Absorbed through 3 Explain the adaptations of the small intestine to increase the surface area for absorption of nutrients. 4 Explain how the following substances can be transported across the plasma membrane. (a) Glucose, galactose and amino acids (b) Fatty acids and glycerol 9.3.2 1/9/2020 12:10:15 PM Biological Lens Liver cirrhosis is a type of liver disease caused by factors such as alcoholic drinks, toxic substances and hepatitis. Liver cells are replaced by scarred cells that can cause failure in the liver functions. Hepatitis is an inflammation of the liver caused by viral infection, toxic substances or autoimmune reaction (Photograph 9.1). The role of the circulatory system The human circulatory system consists of the blood circulation system and the lymphatic system to help transport nutrients to be assimilated. In the assimilation process that occurs in cells, nutrients are used to form complex compounds or structures of components. The blood capillaries in the small intestine combine to form the hepatic portal vein that transports blood to the liver. Lacteals combine to form bigger lymph vessels in the lymphatic system. Then, the contents of the lymph vessels enter the thoracic duct that flows into the left subclavian vein. This lipid is then transported by blood throughout the body. Functions of liver in the assimilation of digested food The liver is the regulator that controls the quantity of nutrients that enter the blood circulatory system. The liver carries out the following functions. METABOLISM OF DIGESTED FOOD Glucose is used for cellular respiration. Amino acids are used for synthesising plasma proteins and enzymes. Through the deamination process, excess amino acids are turned into urea to be excreted through the urine. CHAPTER 9 9.4 Assimilation DETOXIFICATION Activity Zone Conduct a research on the various functions of the liver and produce a scrap book PHOTOGRAPH 9.1 Normal liver and liver of a cirrhosis patient 9.4.1 9.4.2 BioT4(NC)-B9-EN New 7th.indd 153 Liver cells expel toxic substances from the blood. Toxic substances are expelled through the urine. STORAGE OF NUTRIENTS Excess glucose is converted to glycogen to be stored. Normal liver Liver of a cirrhosis patient 153 1/9/2020 12:10:16 PM ASSIMILATION PROCESS IN THE LIVER AMINO ACIDS GLUCOSE The liver synthesises plasma protein and enzymes from amino acids. Excess amino acids cannot be stored in the body and are broken down through the deamination process to form urea which is then expelled. When the glucose supply is insufficient, the liver converts amino acids into glucose. Glucose in the liver is used for cellular respiration when required by the body and the excess is converted to glycogen and stored in the liver. When the glucose level in the blood decreases and the body needs energy, glycogen is converted to glucose. When the glycogen supply reaches a maximum level, the excess glucose is converted to fats. body cell cellular respiration liver amino excess li acids excess glycogen is stored glucose synthesis of plasma proteins and enzymes urea synthesis of protoplasm (in the cell) excreted by hepatic the kidneys portal vein amino acid glucose lipid rol fatty acids + glyce small intestines carbohydrates protein plasma membrane synthesis FIGURE 9.7 Transportation of nutrients and the assimilation in the liver and cells lipid ASSIMILATION PROCESS IN CELLS AMINO ACIDS GLUCOSE Amino acids are used to synthesise new protoplasm and also repair damaged tissues. Amino acids are used to synthesise hormones and enzymes. Glucose is oxidised through cellular respiration to release energy, water and carbon dioxide. Excess glucose is kept as glycogen in muscles. Energy is used for cell processes such as protein synthesis. Formative Practice 9.3 1 State the meaning of assimilation. LIPIDS Lipids such as phospholipid and cholesterol are the primary components that build the plasma membrane. Excess fats are kept in adipose tissues found underneath the skin as stored energy. Fat is oxidised to release energy when there is insufficient glucose. I understand the difference between p 2 Explain the functions of the liver in the assimilation of digested food. 154 BioT4(NC)-B9-EN New 7th.indd 154 9.4.2 1/9/2020 12:10:16 PM 9.5 Biological Lens The large intestine has a huge population of bacteria. There are more than 1000 different species of bacteria in the large intestine and a healthy balance between beneficial and less beneficial bacteria is very important for health and a stable environment in the alimentary canal. Defaecation Functions of the large intestine After the absorption of nutrients is completed in the ileum, undigested food, dead cells, epithelial cells, fibre and water enter the large intestine and move slowly through peristaltic action. Fibre consists of cellulose walls of plant cells. The large intestine carries out two main functions: absorption of water and vitamins colon formation of faeces ABSORPTION OF WATER AND VITAMINS caecum appendix rectum anus CHAPTER 9 Substances absorbed are water and mineral salts metabolic byproducts of some bacteria such as vitamin B, vitamin K and folic acid. FIGURE 9.8 Large intestines FORMATION OF FAECES After the water is absorbed, the remaining waste is a semisolid called faeces. Faeces contains dead cells from the inner layer of the intestine, waste products such as bile pigments, bacteria and toxic substances. The walls of the large intestine secrete mucus to smoothen the movement of faeces until the anus. The movement of faeces takes about 12 to 24 hours before entering the rectum. The faeces will accumulate in the rectum until the pressure in the rectum increases and triggers the need to expel faeces from the body. The rectum muscles will contract to expel faeces from the anus. This process is called defaecation. Brainstorm! What is the effect of antibiotics on the large intestine’s bacterial population? 9.5.1 BioT4(NC)-B9-EN New 7th.indd 155 Formative Practice 9.4 1 State the main function of the large intestine. 2 What are the substances absorbed in the large intestine? 3 Explain the importance of water absorption and vitamins in the large intestine. 4 Explain the formation process of faeces. 155 1/9/2020 12:10:16 PM 9.6 Biological Lens Balanced Diet Energy value in a food sample A balanced diet refers to a diet that consists of all seven food classes (carbohydrates, lipids, proteins, vitamins, mineral salts, fibre and water) in the correct proportion and balanced quantity according to individual needs so that optimal health can be maintained. 1 calorie (cal) = 4.2 joule (J) ENERGY VALUE 1 kilojoule = 1000 joule Across the fields 4.2 J g-1 °C-1 refers to the specific heat capacity of water, that is, the energy required to increase the temperature of 1 g of water by 1 °C. sActivity eit1i.v2itcA9.4 Energy value is the total amount of energy released when one gram of food is oxidised completely. The energy value in food is measured in the form of heat energy, that is, in kilojoule per gram (kJ g-1). Another unit of heat energy is calorie. 1 calorie or 4.2 joule is defined as the quantity of heat energy needed to raise the temperature of 1 gram water by 1 degree Celsius (°C) at a pressure of 1 standard atmosphere. Energy value of food (kJ g-1) = Water mass (g) × 4.2 J g-1 °C-1 × Increase in water temperature (°C) Mass of food sample (g) × 1000 Studying the energy value of food samples Experiment barrier Problem statement Which food sample has the highest energy value? Hypothesis Groundnuts have a higher energy value compared to cashew nuts. thermometer Variables cotton wool Manipulated: Types of food samples Responding: Energy value of food sample Fixed: Water mass Materials Distilled water, food samples (cashew nuts and groundnuts), cotton wool and plasticine Apparatus Retort stand with a clamp, thermometer, boiling tube, long needle, electronic weighing scale, barrier, measuring cylinder and Bunsen burner 156 BioT4(NC)-B9-EN New 7th.indd 156 retort stand boiling tube distilled water food sample needle plasticine 9.6.1 1/9/2020 12:10:17 PM Procedure 1 Weigh a cashew nut using an electronic weighing scale and record its mass. 2 Measure 20 ml of distilled water using a measuring cylinder and pour it into a boiling tube. 3 Clamp the boiling tube to the retort stand and put in the thermometer. 4 Fix the position of the thermometer using cotton wool. 5 Record the initial temperature of the distilled water. 6 Stick the cashew nut on the needle and hold the needle upright using plasticine. 7 Place the barrier around the apparatus set-up. 8 Light the cashew nut using a Bunsen burner and place it below the boiling tube. 9 Stir the water in the boiling tube slowly and record its highest temperature after the cashew nut has completely burned. 10 Replace the water in the boiling tube. 11 Repeat steps 1 to 9 using groundnuts. 12 Calculate the energy value for each food sample using the following formula: Energy value of = Water mass (g) × 4.2 J g-1 °C–1 × Increase in water temperature (°C) food (kJ g–1) Food sample mass (g) × 1000 13 Record your results in the table below. Results Food sample mass (g) Initial temperature of water (°C) Final temperature of water (°C) Increase of Temperature (°C) Energy value of food (kJ g–1) CHAPTER 9 Food sample Cashew nuts Groundnuts Discussion 1 Which food sample shows the highest energy value? 2 State two precautionary steps for this experiment. 3 Compare the energy value of food samples obtained from this experiment with their theoretical energy values. Are there any differences? If yes, explain why. Conclusion Is the hypothesis accepted? Suggest a suitable conclusion for this experiment. The contents of vitamin C in fruit or vegetables juices The nutrient content in various types of food is different. For example, the vitamin C content in fruits and vegetables are different. 9.6.2 BioT4(NC)-B9-EN New 7th.indd 157 157 1/9/2020 12:10:17 PM s1 e.i2 tivit9.5 cA Activity Determining the contents of vitamin C in fruit juice and vegetable juice. Experiment Problem statement Which fruit juice or vegetable juice has the highest content of vitamin C? Hypothesis Orange juice has the highest content of vitamin C compared to lime juice and carrot juice. Variables Manipulated: Types of fruit and vegetable juices Response: Volume of fruit juice or vegetable juice needed to decolourise DCPIP solution Fixed: Concentration of DCPIP solution and concentration of an ascorbic acid solution Materials Orange juice, lime juice and fresh carrot juice, 0.1% ascorbic acid solution, 1% DCPIP solution and distilled water Apparatus Syringe needles (1 ml and 5 ml), knife, 50 ml beaker, specimen tube, juicer and sieve Procedure 1 Put 1 ml of 1% DCPIP solution in a specimen tube. 2 Fill the 5 ml syringe needle with a 0.1% ascorbic acid solution. Ensure that there are no air bubbles trapped in it. 3 Insert the tip of the syringe needle into the specimen tube and drip ascorbic acid drop by drop into the DCPIP solution while stirring slowly until the blue colour of the DCPIP solution is decolourised. ascorbic acid specimen tube 4 Record the volume of the 0.1% ascorbic acid solution needed to decolourise the blue colour of the DCPIP solution. DCPIP solution 5 Repeat steps 1 to 4 twice to get the average volume for each different juice. 6 Record the volume of each juice in the table below. 7 Calculate the concentration of vitamin C of each juice using the following formula. volume of ascorbic acid solution × 0.1% volume of juice used volume of ascorbic acid solution Vitamin C concentration (mg ml-1) = × 1.0% volume of juice used Percentage of vitamin C = Results Volume of solution/juice Solution / Juice required to decolourise DCPIP solution (ml) 1 2 3 Average 0.1% ascorbic acid solution Orange juice Lime juice Carrot juice 158 BioT4(NC)-B9-EN New 7th.indd 158 Vitamin C concentration (%) Vitamin C concentration (mg ml-1) 0.1 9.6.2 1/9/2020 12:10:17 PM Discussion 1 Which juice has the highest content of vitamin C? 2 Why is a 0.1% ascorbic acid solution used as the standard? Conclusion Is the hypothesis accepted? Suggest a suitable conclusion for this experiment. One of the factors that affect the loss of vitamin C content is temperature. Therefore, fruit or vegetables must be kept at a suitable temperature range to preserve vitamin C. the effect of temperature on vitamin C in ivitcStudying A Activity 1.2seit9.6 orange juice Experiment Problem statement What is the most suitable ambient temperature to keep orange juice? Hypothesis Orange juice stored at a low ambient temperature has the highest content of vitamin C. Manipulated: Ambient temperature Responding: Volume of orange juice required to decolourise DCPIP solution Fixed: Volume of DCPIP solution Materials Oranges, 1% DCPIP solution and ice CHAPTER 9 Variables Take Note! Ensure that the juice is not exposed too long to avoid oxidation. Apparatus Specimen tube, knife, syringe needles (1 ml and 5 ml), beakers (50 ml and 100 ml), Bunsen burner, tripod stand, sieve and wire gauze Procedure 1 Prepare 60 ml of orange juice. 2 Label the beakers A, B and C. Pour 20 ml of orange juice into each beaker. 3 Soak beaker A in ice, leave beaker B at room temperature and soak beaker C in boiling water for 30 minutes. 4 After 30 minutes, determine the vitamin C content in the orange juice as shown in Activity 9.5. 5 Calculate the concentration of vitamin C in the orange juice at each different temperature. Results Record your results in an appropriate table. 9.6.2 BioT4(NC)-B9-EN New 7th.indd 159 159 1/9/2020 12:10:17 PM Discussion 1 Is there a difference in the vitamin C content for the juice at different temperatures? 2 What is the effect of temperature on vitamin C in the orange juice? 3 Based on the results, suggest the best way to ensure that you get a high content of vitamin C from fruit juice or vegetable juice. Conclusion Is the hypothesis accepted? Suggest a suitable conclusion for this experiment. Diet modifications for specific individuals A balanced diet for each individual will vary according to lifestyle, health conditions and specific nutritional requirements. Each individual must make wise choices based on a nutrition guide. For example, suggestions for nutritional needs can be made based on Pinggan Sihat Malaysia. Pinggan Sihat Malaysia illustrates the relative quantity of various food classes in a balanced diet (Photograph 9.2). Excessive food intake that is rich in saturated fats can cause health problems such as obesity and cardiovascular diseases. PHOTOGRAPH 9.2 A sample serving based on Pinggan Sihat Malaysia The cause of obesity Obesity is caused by the storage of excess fats as a result of imbalanced food intake and use of energy. Millennial Career Millennial Career Nutritionists are specialists in the field of nutrition who advise specific individuals on suitable diets. Activity Zone Plan meals based on Pinggan Sihat Malaysia for different individuals such as obese individuals, cancer patients and heart patients. 160 BioT4(NC)-B9-EN New 7th.indd 160 Effects of obesity Individuals who are obese need to reduce the intake of carbohydrates and fats as well as increase the intake of vegetables and fruits. Otherwise, a diet with excessive saturated fats and high cholesterol may cause diabetes mellitus and various cardiovascular diseases such as atherosclerosis and hypertension which may result in heart attacks (myocardial infarction) or stroke if not treated. Cancer patients who are undergoing cancer treatment, need to modify their diet to ensure they receive sufficient energy, reduce the risk of infections and enable quick recovery. 9.6.3 1/9/2020 12:10:19 PM 9.7 Health Issues Related to the Digestive System and Eating Habits Adaptation of digestive organs Obesity is a health issue on the rise throughout the world. Although obesity can be controlled through diet management and routine exercise programmes, at times, obesity requires medical treatment. Specialist doctors may suggest surgical procedures to reduce body weight such as gastric bypass (Figure 9.9). A gastric bypass involves a reduction of the stomach size using various methods of surgery. Among the short-term side effects of this surgery are acid reflux, nausea, vomiting, expanded oesophagus, certain food prohibitions and risk of infection. The long-term side effects are dizziness, low blood sugar level, malnutrition, stomach ulcer and defaecation problems. duodenum jejunum gastric sac Part of the stomach that has been bypassed jejunum Part of the duodenum that has been bypassed food digestive juice FIGURE 9.9 Gastric bypass 9.7.1 9.7.2 BioT4(NC)-B9-EN New 7th.indd 161 The food class that is most important in the defaecation process is fibre. Intake of diet that is high in fibre such as fruits and vegetables can smoothen bowel movements. This can prevent health problems such as constipation, colon cancer, rectum cancer and haemorrhoid. Some of the functions of fibre are to: stimulate peristalsis absorb and expel toxic substances regulate the absorption of glucose especially for diabetes mellitus patients increase the population of beneficial bacteria in the large intestine Besides, the intake of a large amount of water can ensure that the faeces stay soft and move easily along the large intestine to aid the process of defaecation. CHAPTER 9 Health issues related to defaecation 161 1/9/2020 12:10:20 PM Health issues related to eating habits Apart from a balanced diet, eating habits also play an important role in fulfilling our energy requirements and maintaining our health. Poor eating habits and an imbalanced diet can cause numerous health problems such as gastritis, muscle dysmorphia, anorexia nervosa and bulimia nervosa. ANOREXIA NERVOSA GASTRITIS Gastritis refers to the inflammation and corrosion of the stomach epithelial layer by gastric juice when there is no food in the stomach. Untreated gastritis can result in gastric ulcers. The causes of gastritis include eating irregular quantities of food at irregular hours and excessive intake of alcohol or painkillers. Anorexia nervosa is quite common amongst teenage girls who are obsessed with their body weight. Anorexics will avoid food to achieve their ideal body weight. They also suffer from psychological problems and nutrient deficiency because of their normal digestive system is affected. MUSCLE DYSMORPHIA BULIMIA NERVOSA For people with bulimia nervosa who are also obsessed with controlling their body weight, they will eat a lot and vomit out the food that they have eaten or take laxatives that cause diarrhoea. In the long run, the patient may suffer from dehydration, nutritional problems and eventually cardiovascular disease or kidney failure. Some individuals feel that their size is small with not enough growth. So, they subject themselves to extreme weightlifting training and exercise. Sometimes, they consume steroids or muscle building supplements. This health issue is called muscle dysmorphia. Activity Zone Do a case study about the following health issues related eating habits: diabetes type 2 obesity acid reflux pica 162 BioT4(NC)-B9-EN New 7th.indd 162 Formative Practice 9.5 1 In your opinion, why is fibre important in the defaecation process. Explain your answer. 2 Predict the effect of modifying digestive organs such as gastric bypass on human health. 9.7.3 1/9/2020 12:10:23 PM Summary NUTRITION AND THE HUMAN DIGESTIVE SYSTEM Digestion Absorption Assimilation Defaecation Balanced Diet Energy value Contents of vitamin C in fruit or vegetables juices Diet modifications for specific individuals Health Issues Related to the Digestive System and Eating Habits The effects of modifying digestive organs on human health Health issues related to defaecation Health issues related to eating habits CHAPTER 9 Digestive System Self Reflection Have you mastered the following important concepts? Structure of the human digestive system Mechanism of digestion Process and products of carbohydrate digestion in the mouth Process and products of protein digestion in the stomach Digestions of carbohydrates, proteins and lipids in the small intestine Adaptations of ileum and villus in the absorption of digested food Assimilation of digested food and liver functions Defaecation Balanced diet and energy value in food samples Diet modifications for specific individuals Health issues related to the digestive system and eating habits 163 BioT4(NC)-B9-EN New 7th.indd 163 1/9/2020 12:10:23 PM Summative Practice 9 1 Some people cannot drink milk because it causes diarrhoea and a bloated stomach. Explain why. 2 Amin had some meat dishes for lunch. Explain how the protein is digested in Amin’s stomach. 3 An individual has the following eating habits: Overeating in a short period of time followed by intentional throwing up on purpose after each meal. Explain how this eating habit can affect the health of this individual. 4 Figure 1 shows the alimentary canal in humans. Z X Y FIGURE 1 (a) Name structures X and Y. (b) (i) The enzymes in X are only effective in an alkaline environment. Explain how an alkaline environment is maintained in X. (ii) Explain how Y is involved in the digestion of carbohydrates in X. (c) Name the enzyme found in Z. Explain how this enzyme functions in the digestion of proteins. (d) A student enjoys eating a lot of oranges. Explain the effect of eating too many oranges on the digestion of starch in X. 164 BioT4(NC)-B9-EN New 7th.indd 164 1/9/2020 12:10:24 PM Essay Questions 5 Explain the processes that fat molecules undergo starting from the duodenum until it is finally used by body cells. 6 A teenager had the following for his breakfast. Buttered bread – 2 pieces Hard-boiled eggs – 2 Fresh milk – 1 glass Apple – 1 Explain what happens to the final digested products of his breakfast in his body cells. 7 (a) Explain why a diet rich in fats is not good for health. (b) Suggest suitable types of food for someone who wants to reduce weight and reduce the risk of contracting cardiovascular disease. Explain your answer. (c) Explain the processes of starch digestion, absorption and assimilation in the human body. Enrichment CHAPTER 9 8 Medicines in the form of capsules are not broken down in the stomach but absorbed easily by the small intestine. When the blood sample of the patient is taken and analysed, it is found that the molecular structure of this medicine is different from its original molecular structure. Explain why. 9 How are drinks with added artificial sweeteners produced and marketed? 10 Nowadays, many individuals prefer ready-to-eat or frozen food products due to their busy lifestyles. Predict the health risks that may arise if these foods are taken continuously for a long period of time and in large quantities. Complete answers are available by scanning the QR code provided 165 BioT4(NC)-B9-EN New 7th.indd 165 1/9/2020 12:10:25 PM