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  1. Activity Book

  2. Practical 12.1Examination of the mammalian alimentary canal and its associated glands Practical 12.2Investigation of the change in pH in the mouth before and after eating candies Practical 12.3 Design an investigation of the action of digestive enzymes Practical 12.4Investigation of the effect of bile salts on oil

  3. Practical 12.5 Stimulation of digestion and absorption in the small intestine using a dialysis tubing STS connection 12.1 Relation of diet, eating habit and oral hygiene to tooth decay STS connection 12.2 ‘Fluoridated water’ versus ‘fluoride toothpaste with calcium’ Activity 12.3 Fate of food in our body Exercise 12 Home Back Next

  4. A Mouth C Stomach E Pancreas G Iieum I Liver K Rectum B Oesophagus D Duodenum F Appendix H Caecum J Colon L Anus 12.1 Examination of the mammalian alimentary canal and its associated glands Questions 1 Identify structures A to L. ANS: 

  5. 12.1 Examination of the mammalian alimentary canal and its associated glands 2 Which processes of nutrition are carried out by the following structures?

  6. 12.2 Investigation of the change in pH in the mouth before and after eating candies Questions 1 Account for the change in pH after eating the candy. ANS:  The oral bacteria convert sugars in the candy to acids. These acids lower the pH of the plaque.

  7. 12.2 Investigation of the change in pH in the mouth before and after eating candies 2 Explain why people who drink soft drinks throughout the day are more likely to have tooth decay. ANS:  Frequent drinking of soft drinks results in a constant attack of the teeth by acids.

  8. 12.2 Investigation of the change in pH in the mouth before and after eating candies 3 Why does the chewing of sugar-free gum may help prevent tooth decay? ANS:  It stimulates the secretion of saliva which can wash off the acids from the plaque and neutralize the acids.

  9. 12.2 Investigation of the change in pH in the mouth before and after eating candies 4 Suggest three ways to reduce the chance of having tooth decay. ANS:  Eat fewer sugary foods. Brush the teeth after eating to remove any food debris. Avoid frequent snacking.

  10. 12.2 Investigation of the change in pH in the mouth before and after eating candies Conclusion What conclusion about the effect of eating candies on the change in pH in the mouth can you draw from this practical? ANS:  Eating candies can lead to a drop in pH in the mouth when the sugars are converted to acids by the oral bacteria.

  11. 12.3 Design an investigation of the action of digestive enzymes Design and perform an experiment 1 At which temperature are you going to conduct your experiment? Why? ANS:  37。C. To simulate the body temperature at which pepsin works well.

  12. 12.3 Design an investigation of the action of digestive enzymes 2 What are the controlled variables in this experiment? ANS:  Number and size of egg white cubes, temperature and total volume of solution, etc.

  13. 12.3 Design an investigation of the action of digestive enzymes 3 What is the independent variable in this experiment? ANS:  The solutions in the test tubes. 4 What is the dependent variable in this experiment? ANS:  The disappearence of egg white cubes.

  14. 12.3 Design an investigation of the action of digestive enzymes 5 What are the controls in this experiment? ANS:  A test tube with an egg white cube, hydrochloric acid and distilled water. A test tube with an egg white cube, sodium carbonate solution and distilled water. A test tube with an egg white cube and distilled water.

  15. 12.3 Design an investigation of the action of digestive enzymes 6 How are you going to record and present the results? ANS:  (Answer varies with Ss.)

  16. 12.3 Design an investigation of the action of digestive enzymes 7 How can you obtain faster results? ANS:  Provide a higher temperature, use smaller egg white cubes instead of a large one, raise the egg white cube from the bottom of the test tube by using a toothpick, etc.

  17. 12.3 Design an investigation of the action of digestive enzymes 8 How can you make sure that the results are reliable? ANS:  Repeat the experiment a few more times.

  18. 12.3 Design an investigation of the action of digestive enzymes 9 What precautions should be taken? ANS:  Make sure that the egg white cubes are well covered with the added solution. Handle hydrochloric acid and sodium carbonate solution with care because they are corrosive.

  19. 12.3 Design an investigation of the action of digestive enzymes Write an experimental report Objective ANS:  To investigate the action of pepsin in protein digestion.

  20. 12.3 Design an investigation of the action of digestive enzymes Procedure 1. Cut the egg white of the hard-boiled egg into 6 small cubes of length 0.5 cm and put 1 in each of the 6 test tubes.

  21. 12.3 Design an investigation of the action of digestive enzymes

  22. 12.3 Design an investigation of the action of digestive enzymes 2. Leave the test tubes in a water bath at 37oC overnight. 3. Observe and note any changes in the size and appearance of the egg white cube in each test tube.

  23. 12.3 Design an investigation of the action of digestive enzymes Results

  24. 12.3 Design an investigation of the action of digestive enzymes Analysis and discussion 1 From the results obtained, deduce where pepsin can be found in the digestive system. ANS:  Stomach. 2 Which class of enzymes does pepsin belong to? ANS:  Protease.

  25. 12.3 Design an investigation of the action of digestive enzymes 3 What are produced as a result of protein digestion by pepsin? ANS:  Peptides. 4 An Albustix paper is dipped into the pepsin solution. Will the result be positive or negative? Why? ANS:  Positive. Pepsin is a protein and it changes the colour of the test end of the paper strip. Home Back Next

  26. 12.3 Design an investigation of the action of digestive enzymes 5 What are the possible sources of errors in this experiment? Suggest ways for improvement. ANS:  (Answer varies with the design.)

  27. 12.3 Design an investigation of the action of digestive enzymes Conclusion ANS:  Pepsin digests proteins in an acidic medium.

  28. 12.4 Investigation of the effect of bile salts on oil Questions 1 Explain the differences in results when the oil is mixed with distilled water instead of bile salt solution. ANS:  Water cannot break down oil into very tiny droplets as the bile salt solution does. Therefore, no emulsion /emulsified fluid is formed and two layers of liquids can be seen. Home Back Next

  29. 12.4 Investigation of the effect of bile salts on oil Conclusion What conclusion can you draw from this practical? ANS:  Bile salts can break down fats into very tiny droplets. It is an emulsifying agent.

  30. 12.5 Simulation of digestion and absorption in the small intestine using a dialysis tubing Questions 1 Why should we wash the outside of the tubing thoroughly with tap water before putting it into the beaker? ANS:  Starch molecules on the outside of the tubing will affect the result. Washing the tubing ensures no such starch molecules are present.

  31. 12.5 Simulation of digestion and absorption in the small intestine using a dialysis tubing 2 Why should a small beaker of water be used to bathe the tubing? ANS:  Less water allows a higher concentration of starch or reducing sugar molecules for easy detection.

  32. 12.5 Simulation of digestion and absorption in the small intestine using a dialysis tubing 3 For the following parts of the model, indicate which parts of the human body they represent.

  33. 12.5 Simulation of digestion and absorption in the small intestine using a dialysis tubing 4 From the results, which substance is found in the water surrounding the tubing? Account for its presence. ANS:  Reducing sugar (maltose) is found. Amylase digests starch into maltose. Maltose molecules are small enough to pass through the tubing and diffuse into the surrounding water, (To be continued.) Home Back Next

  34. 12.5 Simulation of digestion and absorption in the small intestine using a dialysis tubing …… continued from previous page whereas the large starch molecules are retained by the tubing.

  35. 12.5 Simulation of digestion and absorption in the small intestine using a dialysis tubing 5 From the results obtained, why do you think digestion is needed? ANS:  Through digestion, food substances are broken down into small molecules that can diffuse into the blood for use in our body.

  36. 12.5 Simulation of digestion and absorption in the small intestine using a dialysis tubing 6 Comment on the limitations of this model in demonstrating digestion and absorption in the small intestine. ANS:  Maltose molecules are not small enough to pass through the small intestine.The small intestine can secrete enzymes but the model cannot. (To be continued.)

  37. 12.5 Simulation of digestion and absorption in the small intestine using a dialysis tubing …… continued from previous page The small intestine shows peristalsis but the model does not.There are many types of food molecules in the small intestine apart from starch.The food molecules have to pass through more than one layer of cells instead of only one layer of tubing.The blood is enclosed in blood vessels.

  38. 12.5 Simulation of digestion and absorption in the small intestine using a dialysis tubing 7 Suggest some methods to obtain faster results. ANS:  Diffusion rate of the reducing sugar molecules can be increased by stirring the surrounding water and using a water bath at a higher temperature. (To be continued.)

  39. 12.5 Simulation of digestion and absorption in the small intestine using a dialysis tubing …… continued from previous page More concentrated solutions of starch and amylase can be used to speed up the reaction rate.

  40. 12.1 Relation of diet, eating habit and oral hygiene to tooth decay Task 1 1 Tooth decay is more common in molars. Why? ANS:  It is because food debris is easily trapped between the cusps and in the pits. Moreover, the toothbrush is difficult to reach the molars at the sides of the jaws to brush off the food debris.

  41. 12.1 Relation of diet, eating habit and oral hygiene to tooth decay 2 Will foods rich in starch, such as bread and crackers, cause tooth decay? Explain your answer. ANS:  Yes. Starch is broken down into sugars by the salivary amylase. These sugars can be used by the oral bacteria to produce acids.

  42. 12.1 Relation of diet, eating habit and oral hygiene to tooth decay 3 The dentist suggested Kenny not to eat too many raisins. Do you know the reasons? ANS:  Raisins contain sugars which can be used by the oral bacteria to produce acids. Raisins are sticky and they tend to stay on the teeth. The longer the exposure of the sugary food to the oral bacteria, the more the acids will be produced. Home Back Next

  43. 12.1 Relation of diet, eating habit and oral hygiene to tooth decay 4 How should Kenny change his snacking habit to prevent tooth decay? ANS:  Snack on foods such as milk, cheese or apple that are good for teeth. Limit the period of time taking the snack. Reduce the number of snacking between meals, serve as desserts during meals as far as possible.

  44. 12.1 Relation of diet, eating habit and oral hygiene to tooth decay 5 If you were the dentist, what would you suggest to Kenny for keeping good oral hygiene? ANS:  Use dental floss to remove food debris that is not easily brushed off by the toothbrush. Have a dental check-up twice a year.

  45. 12.2 ‘Fluoridated water’ versus ‘fluoride tooth paste with calcium’ Task 1 Suggest why fluoridated water is particularly beneficial to the low-income people. ANS:  The low-income people are less likely to have regular dental check-up and practise good oral hygiene by using the oral care products. (To be continued.)

  46. 12.2 ‘Fluoridated water’ versus ‘fluoride tooth paste with calcium’ …… continued from previous page Drinking fluoridated water is an inexpensive way to prevent tooth decay.

  47. 12.2 ‘Fluoridated water’ versus ‘fluoride tooth paste with calcium’ 2 In a study carried out in 1999, tooth decay was shown to decline in both communities with and without fluoridated water. Can you suggest an explanation? ANS:  The widespread use of fluoride toothpaste. / Increased awareness of dental health among people.

  48. 12.2 ‘Fluoridated water’ versus ‘fluoride tooth paste with calcium’ 3 Do you think the addition of calcium to fluoride toothpaste can offer ‘extra’ protection? ANS:  Yes. It increases the amount of calcium in the saliva. This drives the equilibrium towards the replacement of the mineral to the enamel. (To be continued.)

  49. 12.2 ‘Fluoridated water’ versus ‘fluoride tooth paste with calcium’ …… continued from previous page / No. The calcium does not stay long in the mouth to produce an effect.

  50. 12.2 ‘Fluoridated water’ versus ‘fluoride tooth paste with calcium’ 4 Would you suggest fluoridated water or fluoride toothpaste with calcium to a 3-year old child? Explain your choice. ANS:  Fluoridated water. It offers longer-lasting protection and is cheap. The child may swallow the toothpaste if he brushes his teeth with toothpaste. (To be continued.) Home Back Next