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S E C T I O N 10.3 The Chemical Digestion of Food H 2O HO H 2O E X P E C TAT I O N S List the three types of enzymes associated with chemical digestion. Proteases proteases protein + water Design an activity to show that enzymes are not used up when involved in a reaction. H 2O O O H 2O O O HO O H carbohydrases Carbohydrases H 2O Describe how hormones and the nervous system regulate the release of enzymes. H 2O complex sugar + water proteins, carbohydrates, and lipids is greatly speeded up by enzymes. The smaller molecules produced as a result can pass through cell membranes. fat + water H 2O H 2O As food moves through the digestive tract to be physically broken down into smaller and smaller pieces, it is also being acted upon by digestive chemicals. These chemicals work to break complex molecules into smaller ones that can pass through cell membranes. Chemical Digestion and Enzymes The term digestion is usually applied to the chemical breakdown of food by the process of hydrolysis. During hydrolysis, a water molecule is added at the point where a link in a more complex molecule is being broken (Figure 10.17). Hydrolysis can occur spontaneously at a very slow rate, but it is immediately speeded up by enzymes. These enzymes are biological catalysts which, being proteins, are manufactured in the ribosomes of cells. Wo rd LINK “Hydrolysis” comes to us from two Greek words: hydro, meaning “water,” and lysis, meaning “to loosen.” In other words, hydrolysis means to break apart with water. REWIND For more information about enzymes and their action, return to Chapter 2, Section 2.2. amino acid molecules O H H HO simple sugar molecules HO HO H HO O H O O O H HO HO glycerol molecule H 2O Figure 10.17 Hydrolysis of H H H HO Lipases lipases glycerol + fatty acids H HO H H HO HO fatty acid molecules As shown in Figure 10.17, three kinds of enzymes are associated with digestion: carbohydrases, lipases, and proteinases. Each is named after the class of compounds (carbohydrates, lipids, and proteins, respectively) that it helps to break down. These enzymes are formed by secretory cells and then secreted into the digestive tract. The secretory cells can exist singly, in simple sacs, or in the lining of the walls of glands. A gland is a structure made up of a complex system of tubules (see Figure 10.14). The digestive glands are usually connected to the digestive tract by ducts. Hydrolytic enzymes act very specifically. They catalyze hydrolysis for only particular linkages. For example, the fat-splitting lipase can act on a wide variety of lipid compounds, but in each case the same linkage is hydrolyzed. These digestive enzymes often require special conditions in order to act. Some perform best in acid media, for instance, while others work best in neutral or alkaline media. Other chemicals, such as sodium carbonate and bicarbonate, are often secreted with the hydrolytic enzymes. These chemicals assist in establishing and maintaining the pH level at which the enzymes work best (see Appendix 9 to review pH). Enzymes are adversely affected by high temperatures. Many also require the presence of metallic ions (such as those of cobalt and magnesium), vitamins, or coenzymes in order to function properly. Nutrients, Digestion, and Nutrition • MHR 343 PAUSE Digestive Enzymes RECORD The contents of the stomach are very acidic, with a pH of around 2. A short distance farther on in the duodenum, however, the contents that have left the stomach are slightly basic, with a pH of around 8. What could account for these dramatic differences in pH, and why do you think the body maintains the contents of these organs at these pH levels? DESIGN YOUR OWN Investigation Most of the digestive enzymes that we know today have been named by starting with the substrate they attack and adding an “-ase” ending. A substrate is a molecule on which an enzyme acts. Thus, the enzyme maltase acts on the sugar maltose, its substrate. Other enzymes discovered SKILL FOCUS 1 0 • A Initiating and planning Factors That Affect the Rate at Which Enzymes Act Hypothesizing Identifying variables Catalase is a non-digestive enzyme produced by the liver. It breaks down the toxin hydrogen peroxide in the body according to the Catalase H2O + O2 . The presence of the flammable gas equation H2O2 oxygen can be used to detect this reaction. The volume produced can be used to calculate the rate of the enzyme’s activity. In this investigation, you will design experiments to test for factors that may affect the rate of this reaction. Factors to consider include pH, temperature, the quantity of the substrate hydrogen peroxide, and the quantity of the enzyme. Test for each factor separately. Problem How do different factors affect the rate of enzyme activity? Hypothesis CAUTION: Hydrogen peroxide is a bleaching agent and an irritant. Take care not to get it, the vinegar, or the sodium bicarbonate solutions in your eyes or on your skin or clothes. Wash spills away immediately with lots of water and inform your teacher. Exercise caution when testing for flammable gas. Make sure there are no cracks in the glassware you use. Materials 344 Analyzing and interpreting dilute hydrogen peroxide solution (substrate) (3%) matches wooden splints Experimental Plan Make hypotheses about three factors you would like to test. 30 mL square bottle one-holed rubber stopper to fit above 100 mL graduated cylinder 10 mL graduated cylinder plaster tray or pneumatic trough forceps 600 mL beaker watch or clock absorbent paper disks Performing and recording stock solution of puréed liver (contains catalase) medicine dropper vinegar (acid) sodium hydrogen carbonate solution (base) graph paper MHR • Internal Systems and Regulation 1. Using the materials and considering the set-up shown in the illustration, prepare a list of possible ways in which you can test your hypotheses. 2. Decide on an approach that you can carry out in your classroom. 3. Make sure your approach will test for only one possible factor (independent variable) at a time. Prepare to collect and record quantitative data for at least three variables on the graph paper, and to summarize this data in a data table (like the one shown here) that can be interpreted by others. Independent variable Elapsed time Volume of gas evolved Gas flammable? many decades ago, such as pepsin, are known by their original, trivial names. Known human digestive enzymes, and their places of origin and activity, substrates, and products are listed in Table 10.1 on the following page. More digestive enzymes will likely be discovered as our knowledge of body chemistry increases. 4. Outline a procedure for your experiment listing each step. Include all necessary safety procedures. Provide a list of materials and the quantities you will require. Obtain your teacher’s approval before starting any reaction. One step you must do is soak as many of the paper disks in the puréed liver extract as you think you will need. Make sure you soak them all for the same length of time. To begin the reaction, the bottle containing the hydrogen peroxide and disks is turned over. Wash your hands thoroughly at the end of the investigation. COURSE CHALLENGE If you have not yet done a dissection (or a virtual dissection) of the digestive system of a vertebrate, this is a good time to do so. A fetal pig dissection guide is presented in Appendix 10. Keep in mind how you might use knowledge and skills gained from this dissection to assist you in your Biology Course Challenge on forensic science. Data and Observations Conduct your investigation and make your measurements. Graph your results first, and then enter your summary data in the table. Analyze 1. Changes in which factors (independent variables) influenced the rate at which gas was produced? Which changes, if any, meant that little or no gas was produced? 2. Changes in which factor produced the greatest amount of gas in the shortest amount of time? forceps catalasesoaked discs hydrogen peroxide 3. Why was it necessary to test only one variable at a time? Conclude and Apply oxygen graduated cylinder turn bottle to 180° to activate Checking the Plan 1. What will be the dependent variable for each of the independent variables you want to test? What will the controlled variables be? 2. What will be your control? 3. What will you measure, and how will you record this information on the graph paper? 4. How will you safely test whether any resulting gas is flammable? 4. Based on your results, which factors affect the rate at which enzymes such as catalase act? 5. Explain how variations in these factors could affect digestive enzymes, and how they could affect the general well-being of a person. Exploring Further 6. Ask a pharmacist at a local drugstore to show you some of the products intended for use by customers with digestive problems. How many of these products contain digestive enzymes, mild acids, or mild bases? Explain why these ingredients might be used in these products, in light of what you have learned about factors that affect the rate at which enzymes work. 7. Why do you suppose the human body is kept at a near constant temperature of 37˚C? Could it have anything to do with enzymes? Do some research to find out more. Nutrients, Digestion, and Nutrition • MHR 345 Table 10.1 Enzymes of the human digestive system Enzyme Place where enzyme acts Substrate Products Origin of enzyme salivary amylase (also called ptyalin) mouth starch, glycogen maltose (a double sugar) salivary glands pepsin stomach protein peptides a product of pepsinogen and hydrochloric acid, both secreted by stomach glands lipase small intestine fats glycerol and fatty acids secreted by stomach glands but not very active in the stomach (too acid) pancreatic amylase (also called amylopsin) small intestine starch maltose pancreas pancreatic lipase (also called steapsin) small intestine fat glycerol and fatty acids pancreas trypsin small intestine peptides simpler peptides product of trypsinogen from the pancreas, and of enterokinase from the walls of the duodenum chymotrypsin small intestine peptides simpler peptides product of trypsin and chymotrypsinogen (from the pancreas) carboxypeptidase small intestine peptides simpler peptides pancreas ribonuclease small intestine ribonucleic acid nucleotides pancreas deoxyribonuclease small intestine deoxyribo-nucleic acid nucleotides pancreas aminopeptidase small intestine peptides simpler peptides glands in the walls of the small intestine tripeptidase small intestine tripeptides dipeptide and an amino acid glands in the walls of the small intestine maltase small intestine maltose two glucose molecules glands in the walls of the small intestine sucrase small intestine sucrose one molecule of glucose and one of fructose intestinal glands lactase small intestine lactose one molecule of glucose and one of galactose intestinal glands A Summary of Chemical Digestion In humans and other mammals, chemical digestion begins in the mouth, where the enzyme, amylase, breaks down starch to smaller disaccharide sugar molecules. In the stomach, gastric juice contains hydrochloric acid and the enzyme, pepsin. Pepsin begins the breakdown of protein in the stomach while the amylase swallowed from the mouth continues breaking down starch until the pH in the stomach becomes too low for it to act (see Appendix 9 for a review of pH). Pepsin functions well within a pH range of 1 to 2. Amylase requires a high pH to function. The thick liquid chyme then passes into the small intestine, a muscular tube about 6 m in length. The first 25 cm, called the duodenum, secretes enzymes from its lining, and the pancreas and liver both empty their enzymes into the duodenum to complete the process of digestion. 346 MHR • Internal Systems and Regulation Pancreatic juice is alkaline and thus neutralizes the acidity of partially digested food coming from the stomach, stopping any further action of pepsin. (Again, refer to the table above to see the wide variety of enzymes secreted and used to digest food.) As noted previously, no enzymes are produced in the large intestine; water is simply absorbed from indigestible material through its walls. Anaerobic bacteria living there, however, do digest more of this material, and some of it is absorbed for use by the body, as well. These bacteria also synthesize some B vitamins and Vitamin K which is then used by the body. The total digestion of a large meal takes about 24–33 h. The Regulation of Digestive Secretions The secretion of digestive enzymes is regulated by both nerves and hormones. A hormone is a returning gastrin stimulates gastric glands to release more gastric juice vagus nerve fiber nerve impulses stimulate the release of gastric juice from gastric glands impulses also stimulate the release of gastrin, which is transported in the bloodstream Figure 10.18 The secretion of gastric juices is controlled by nerve impulses and the hormone gastrin. chemical regulator that is secreted in one part of the body and transported by the bloodstream to another part, where it causes a response. For instance, the digestive glands lining the walls of the stomach are stimulated by nerves and by a hormone called gastrin (Figure 10.18). In response, individual glands secrete mucin (which both lubricates food and protects the walls of the stomach), pepsin, hydrochloric acid, and lipases. The glands that produce gastrin are located in the lower part of the stomach. Because these glands are ductless, however, the hormone must be transported by the bloodstream until it arrives at the upper part of the stomach before it is able to stimulate the digestive glands to secrete their products (Figure 10.19). carbonate and sodium bicarbonate. This fluid raises the pH of the chyme from 2 to approximately 8. gastrin liver secretin CCK gallbladder duodenum stomach pancreas blood vessel BIO FACT Secretin, identified by William Bayliss and Ernest Starling in 1902, has the honour of being the first hormone ever discovered. Find out how Bayliss and Starling made this discovery by doing library and/or web-based research. Start at the following web site. www.school.mcgrawhill.ca/resources/ In a similar way, the presence of the chyme in the duodenum stimulates ductless glands in the walls of the duodenum to secrete the hormone secretin into the bloodstream. Arriving at the pancreas, secretin stimulates duct cells there to release an alkaline fluid containing sodium Figure 10.19 Gastrin, secretin, and CCK are hormones produced by ductless glands. All must be transported by the bloodstream from their place of origin to the place where they can stimulate the release of digestive juices. Trypsin, one of the enzymes produced by the pancreas, requires a pH of approximately 8 to function efficiently. At this pH, pepsin is no longer functional. Secretin, along with the hormone cholecystokinin (CCK, which is also produced in the walls of the duodenum), also causes the pancreas to secrete its enzymes and the gall bladder to secrete bile. Nutrients, Digestion, and Nutrition • MHR 347 Investigation SKILL FOCUS 1 0 • B Predicting Digestion of a Protein Performing and recording Digestion involves the breakdown of a substance to the point where its nutrient products can be absorbed into the bloodstream and carried to the individual cells where they can be used. Proteins are complex molecules, and several enzymes and other chemicals are involved in their digestion. Two protein-digesting enzymes are pepsin, secreted in the stomach, and trypsin, secreted in the pancreas. Trypsin is a component of pancreatin, along with pancreatic amylase and lipase. In this investigation, you will explore some of the conditions under which these digestive enzymes work. As with fats and carbohydrates, the chemical digestion of protein takes place by means of hydrolysis. Pre-lab Questions Analyzing and interpreting Procedure What happens during hydrolysis? What kind of molecules are formed when proteins undergo hydrolysis? Problem 1. Coagulate a small quantity of egg white by placing it in a beaker of boiling water. Divide the coagulated product into 9 small cubes. Place the egg white cubes into separate test tubes, and number the tubes 1 through 9. How can you demonstrate that pepsin and trypsin (in pancreatin) will digest protein? cubes boiled egg white Prediction Predict the kind of environments that pepsin and trypsin require in order to digest egg white, which is essentially protein. CAUTION: Hydrochloric acid is a strong acid and sodium hydroxide is a strong base. Both are very corrosive and must not be mixed together. Other chemicals used may be toxic. Be extra careful not to get them in your eyes, on your skin, or on your clothes. Flush spills away immediately with lots of water and inform your teacher. Exercise care with boiling water and hot objects. Materials 4 beakers (250 mL) Bunsen burner ring clamp wire gauze retort stand 12 test tubes egg white pepsin solution (1%) pancreatin solution (1%) acid-base indicator (bromthymol blue, litmus, or congo red) 348 dilute hydrochloric acid (1%) distilled water sodium hydrogen carbonate solution (1%) copper (II) sulfate solution (1%) dilute sodium hydroxide solution (1%) MHR • Internal Systems and Regulation 2. Test the egg white samples in the test tubes by adding the following substances: Test tube 1 — 5 mL of distilled water Test tube 2 — 5 mL of distilled water and 1 mL of 1% sodium hydrogen carbonate solution Test tube 3 — 5 mL of distilled water and 1 mL of hydrochloric acid Test tube 4 — 5 mL of 1% pepsin solution Test tube 5 — 5 mL of 1% pepsin solution and 1 mL of 1% sodium hydrogen carbonate solution Test tube 6 — 5 mL of 1% pepsin solution and 1 mL of dilute hydrochloric acid Test tube 7 — 5 mL of 1% pancreatin solution Test tube 8 — 5 mL of 1% pancreatin solution and 1 mL of 1% sodium hydrogen carbonate solution Test tube 9 — 5 mL of 1% pancreatin solution and 1 mL of dilute hydrochloric acid (1%) 3. Set the test tubes aside for 24 h in a place where the temperature can be kept as close to 37˚C as possible. Observe their contents after the elapsed time, and then add a few drops of an acid-base indicator. Record the approximate pH in a data table like the one shown here. Test tube Observed results and pH Biuret colour change? 1 2 3 etc. 4. Although the end products of protein digestion cannot be obtained through a single enzyme reaction, you can confirm that intermediate products have been produced by testing for them with a Biuret solution. Make this solution just before using it by adding two or three drops of a 1% copper (II) sulfate solution to 3 mL of a 1% sodium hydroxide solution. Carefully pour approximately 3 mL of liquid from each of the test tubes and replace it with approximately 3 mL of the Biuret solution. Test tubes whose contents change colour contain partially digested protein. Make sure to record your observations in the table. Wash your hands thoroughly at the end of the investigation. Post-lab Questions 1. What was the purpose of adding sodium hydrogen carbonate solution to test tubes 2, 5, and 8? 2. According to the Biuret solution test, which test tubes showed evidence of protein digestion? 3. In which test tube was the digestion of protein most evident? What does this suggest about the action of protein digestion enzymes in our stomachs? 4. In what pH range does the digestion of protein occur most favourably? By inference, what must be the approximate pH of the chyme in our stomachs? 5. Explain why is it necessary to have more than one enzyme in order to fully digest a protein. Conclude and Apply 6. What were the controls in this investigation? Why were they necessary? Exploring Further 7. You can demonstrate the presence of protein-digesting enzymes in plant material by adding 10 mL of fresh or frozen pineapple juice to a test tube containing a small piece of egg white and allowing it to stand for 24 h. Set up a second test tube using distilled water in place of the fresh or frozen juice, and a third test tube using boiled pineapple juice. What effect did boiling the pineapple juice have on its effectiveness as a protein digester? What was the purpose of the second test tube? 8. Cuts of meat that would otherwise be tough are often treated with meat tenderizers before they are cooked and served. Do some research to find out more about meat tenderizers and how they work. 9. You arrive home after a few days away during a heat wave to find you had left fresh fish fillets uncovered on the kitchen counter. What you see and smell is hardly appealing or palatable, but decay organisms seem to be having a feast. How are these organisms able to do what they do? Why would the story have been different if you had remembered to put the fish in the refrigerator? Nutrients, Digestion, and Nutrition • MHR 349 PAUSE RECORD You are walking down the street at dinnertime. You begin to smell the pleasent aroma of cooking food. Suddenly, your mouth starts to water. Explain what you think might be causing this reaction. How Do We Know What We Know? The process of digestion in human beings is now well known and well understood. This was not always the case. Of the early research that was done, we only know about that which was published. In 1833, an innovative physician took advantage of a patient’s situation to provide some important early information about how digestion occurs. William Beaumont (1785–1853) had, as a patient, a man who had been shot in the stomach. When his gunshot wound healed, it did so improperly. The lining of his stomach fused to the outer wall of his body, leaving a small opening (or fistula) to his stomach. Beaumont used this man for a series of studies of digestive processes. He introduced specific foods directly into the stomach through the opening, always with a string attached. Beaumont was able to ascertain from this the relative rates of digestion for different kinds of foods. He also noted that the stomach produces gastric juice, and identified the acid in it as hydrochloric acid. He noted the movements of the stomach and was probably the first person to report the effects of the emotions on the secretion of gastric juice. Beaumont’s experiments stimulated many others to begin to investigate digestion and nutrition. Most of these used other animals as subjects, and over the next two hundred years, led to our present understanding of how digestion occurs. The Roles of Related Organs Three other organs associated with the digestive tract are the liver, pancreas, and gall bladder. These organs play vital roles in the digestive process. The liver also carries out many other functions essential to the body’s general good health, some of which have an impact on the digestive process. The Liver In its digestive role, the liver is responsible for producing bile salts from cholesterol. These bile salts are released into the small intestine as needed, where they break up fat globules into tiny fat droplets. This allows a stable emulsion of the droplets to form in the contents of the intestines. 350 MHR • Internal Systems and Regulation The action is similar to the action of detergent on greasy pots and pans — the detergent breaks up the grease into fine droplets that form an emulsion with water, allowing the emulsion to be washed away. The tiny fat droplets in the small intestine are much more readily acted on by the water-soluble enzyme lipase, which the bile salts also activate. Evidence suggests that the fatty acid and glycerine molecules that result are engulfed through pinocytosis by the epithelial cells of the villi. Once inside the villi, the fatty acid and glycerine molecules enter the very porous lacteal vessels, where they frequently reunite to make fat molecules. These molecules are then transported by the lacteal vessels through the lymphatic circulatory system and into the main bloodstream near the left shoulder. A high percentage of fats may even be emulsified and absorbed directly, without the need for lipase action. BIO FACT The liver is the largest organ in the body and has been identified as having over 500 different functions. The liver also functions as a demolitions expert, recycler, storehouse, and detoxification centre in addition to performing many other tasks. As a demolitions expert, it breaks down old red blood corpuscles, after which the hemoglobin component of the old cells is further broken down. Then, in its function as a recycler, parts of the decomposed hemoglobin molecules are used to make bile salts. As a storehouse the liver collects from the bloodstream chemicals that are in excess of the amount needed by the body at any given time. All monosaccharides except glucose, for instance, are removed and converted into glycogen by the liver. This glycogen is stored, then reconverted as needed to keep the glucose level in the bloodstream constant. The fat-soluble vitamins A, D, E, and K are also stored in the liver. Because the body cannot store amino acids, any excess must be de-aminized or broken down into smaller molecules. Some of these molecules are converted to fats, while others are eliminated from the body (see Figure 10.20). As a detoxification centre, the liver works to detoxify various poisons ingested with food and drink in addition to those produced in the intestines. The liver is, in short, a marvellous and highly evolved organ that performs a wide range body cells respiration fat cells enzymes structural proteins fats respiration glucose (as needed) fatty acids and glycerol pyruvic acid and other products glycogen fats urea to kidneys excess amino acids excess glucose blood flow amino acids glucose blood vessel small intestine Figure 10.20 The liver plays many roles in the digestive process. Shown here are some of the paths taken by the products of carbohydrate and protein digestion that enter the liver. of important, specialized functions for the body as a whole. The Pancreas Like the liver, the pancreas is an important member of “Team Digestion.” As shown in Table 10.1, the pancreas is the source of several enzymes that act on carbohydrates, fats, and peptides, all of which are sub-units of proteins. As mentioned earlier, the pancreas also produces and releases a basic solution that changes the pH of chyme (from a strongly acid mixture to a weakly basic one) after it enters the duodenum. The Gall Bladder Like every successful team, the contributions of each and every member matter. The gall bladder, although not involved in enzyme production, serves as the storage warehouse for bile produced in the liver. Bile contains a number of chemicals that include cholesterol and the bile salts so important to the digestion of fats. The release of bile from the gall bladder is triggered by a hormone that stimulates the contraction of the smooth muscle cells of the gall bladder and makes the sphincter muscle at the neck of the gall bladder relax. This relaxing of the sphincter muscle allows the bile to enter the duodenum via the bile duct. As this is happening the hormones CCK and secretin, produced in the duodenum, inhibit the contraction of the stomach muscles, thus putting the stomach into a temporary resting condition. As lipids are absorbed by the intestine, so are the components of bile. They are picked up in blood vessels, carried back to the liver, and recycled to make more bile. Back to the Plants This section has concentrated on digestion in human beings. Other heterotrophs similarly must have digestive systems to break down their food. Even green plants (which, as autotrophs, are capable of producing their own starch, proteins, and fats) need some way to digest or convert these substances into a soluble form for transport to the rest of their cells. For example, food stored as insoluble starch in the cotyledons (embryonic leaves) of a very young seed-bearing plant must first be converted to soluble sugar before it can be transported to an actively growing part of the plant (see Figure 10.21). Thus, although the solution for how to obtain food varies, the problem of deriving Nutrients, Digestion, and Nutrition • MHR 351 and transporting nutrients to the cells remains the same for all living organisms. In fact, every living organism must either bring its cells to the source of its life-supporting nutrients or carry those nutrients to its cells. first true leaves cotyledon hypocotyl seed coat FAST FORWARD For more about plant nutrition and growth, turn to Chapter 16, Section 16.1. Figure 10.21 Food stored as starch in the cotyledons of this bean seed is being converted to sugar for the use by the growing leaves and roots. SECTION 10. K/U What kinds of conditions affect the action of enzymes? C Create a concept map that shows the relationship among the three accessory organs of the digestive system. 11. K/U How are hormones transported and what do they do? K/U Describe at least four different functions of the liver. 12. 1. K/U Name the three kinds of enzymes associated with digestion. 2. 3. 4. K/U Describe the role played by the nervous system in the secretion of gastric juices. 5. K/U Why are most digestive enzymes not found in the stomach? 6. Create a line graph showing the comparative length of the esophagus, small intestine, and large intestine. Under each segment, offer explanations for why it is longer or shorter than its neighbours. 7. 352 REVIEW C MC A condition called heartburn afflicts many people occasionally. What causes this malady, and what can people do about it? 8. I A student has placed the enzyme lipase in a test tube along with a solution of hydrochloric acid and a protein. Explain why digestion will or will not take place. 9. I Describe an activity that could be used to test whether or not an enzyme is used up in a reaction. MHR • Internal Systems and Regulation K/U What does the gall bladder do? 13. MC Cirrhosis of the liver is a serious disease. What environments and lifestyle choices can put someone at risk for this condition? How would it affect the person’s health? 14. C Some foods we eat contain toxins, or poisons. Explain why we do not normally suffer from the effects of these toxins. 15. C Create a diagram showing the accessory organs and their ducts in relation to the stomach and small intestine. 16. MC As a result of a major car accident, the pancreas of an injured driver has been badly damaged. What role does the pancreas play in the digestive system? What will happen to the driver if he loses his pancreas? Could a person live without one? Explain, giving reasons. 17. MC An older friend of the family has just had her gall bladder removed. Describe the kind of diet you think she would be wise to follow.