Digestion, Absorption and Enzymes

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Secondary 1 Biology lesson materials on topic of Digestion

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  • Question to Students: Why do we need to eat?In which types of food can we find the various nutrients?
  • Question to Students: Why do we need to eat?In which types of food can we find the various nutrients?
  • Question to Students: Why do we need to eat?In which types of food can we find the various nutrients?
  • Digestion, Absorption and Enzymes

    1. 1. Digestion
    2. 2. Learning ObjectivesAt the end of this lesson, you should be able to:• explain what is meant by digestion• explain why food must be digested• define enzymes as biological catalysts that speed up therate of reactions without being chemically changed at theend of the reaction• explain the effects of temperature on enzyme activity• explain the mode of enzyme action in terms of the lock-and-key hypothesis
    3. 3. Why EAT?We need to eat because… Our body needs NUTRIENTS CARBOHYDRATES PROTEINS FATS Types of Nutrients the Body Needs
    4. 4. Why EAT?CARBOHYDRATES PROTEINS FATS Types of Nutrients the Body Needs
    5. 5. Why EAT?CARBOHYDRATES PROTEINS FATS Types of Nutrients the Body Needs
    6. 6. Why DIGESTION?
    7. 7. Why DIGESTION?Digestion is necessary- to break down large insoluble molecules into smallermolecules- so that the body can absorb the nutrients required for itsfunctioning DIGESTION is the process whereby large, insoluble food molecules are broken down into smaller, soluble food molecules
    8. 8. Large Complex Insoluble Molecules DIGESTION Small Simple Soluble Molecules Starch Glucose carbohydrase Proteins protease Amino Acids lipase Fats Glycerol Fatty Acids
    9. 9. DIGESTION These small simple soluble Glucose molecules are used for the following purposes: • Growth of new cells and tissues • Provide energy for Amino Acids growth, movement and for keeping warm • Repair damaged tissues • Keep us healthyGlycerol Fatty Acids
    10. 10. Food Tests• To test whether certain nutrients are present in a certain food, specific tests can be conducted.• Iodine solution can be used to test if there is starch present in food.• Benedict’s solution can be used to test if there is reducing sugar (eg. Glucose) present in food.
    11. 11. FOOD TESTS• STARCH test • Add about 5 drops of iodine solution to the sample to be tested. • If starch is present, the iodine will turn dark blue • If starch is absent, the iodine will remain brown
    12. 12. FOOD TESTS• REDUCING SUGAR test • Add 2cm3 of Benedict’s Solution to 2cm3 of the sample solution in a test-tube. • Heat the test-tube in a boiling water bath for 2-5 minutes. • If reducing sugar is present, the solution produces a brick-red precipitate. • If reducing sugar is absent, the solution remains blue.
    13. 13. ENZYMES Enzymes are biological catalysts.A A Catalysts are substances that speed up the rate of reactions, but themselves remain chemically enzyme unchanged at the end of the reaction. A AA A enzyme enzyme
    14. 14. Lock & Key Hypothesis Substrate A Enzyme Enzyme Substrate B Enzyme Enzyme
    15. 15. ENZYMES- Mechanism substrate LOCK and KEY hypothesis • Specificity: One enzyme binds to Enzyme only one substrate • Reusable: They are chemically unchanged at the end of the reaction products • Required in minute amounts • Sensitive to temperature and pH Enzyme
    16. 16. ENZYMES- Mechanism substrate Enzyme-substrate Enzyme complex products Enzyme
    17. 17. ENZYMES- Mechanism substrate • In an enzyme reaction, the reactants are called substrates. • Every enzyme has an active site, which is the place where the substrate will bind with the enzyme. Enzyme • This active site has a specific 3- dimensional shape. • The active site only allows substrates with the complementary products shape to fit in, just like how a key fits into the lock. • Enzyme is the LOCK and substrate is the KEY. Enzyme
    18. 18. ENZYMES- Mechanism substrate • The enzyme and substrate molecules will combine to form a temporary structure called the enzyme-substrate complex. • When substrate binds to the Enzyme enzyme, the enzyme will then react to convert the substrate into product(s). • The product(s) then separates from products the enzyme leaving the enzyme free to combine again with more substrates. Enzyme
    19. 19. ENZYMES- Mechanism substrate • Product formed no longer fit into the active site and are released. • The active site is now free to receive more substrate molecules. • In conclusion, enzyme action is Enzyme specific due to the shape of the substrate and active site being complementary to each other. products Enzyme
    20. 20. Lock & Key Hypothesis
    21. 21. ENZYMES- Factors Enzymes work best at their optimum temperature.Rate of Enzyme Activity At low At high temperatures, en temperatures, en zymes are zymes are inactivated. denatured. Temperature/ °C
    22. 22. ENZYMES- Factors Enzymes work best at their optimum pH.Rate of Enzyme Activity At extreme pH, enzymes are denatured. pH
    23. 23. Learning ObjectivesAt the end of this lesson, you should be able to:• explain what is meant by digestion• explain why food must be digested• define enzymes as biological catalysts that speed up therate of reactions without being chemically changed at theend of the reaction• explain the effects of temperature on enzyme activity• explain the mode of enzyme action in terms of the lock-and-key hypothesis
    24. 24. LEARNING OBJECTIVES You should now know how to: - identify the main organs in the human digestive system - describe the process of digestion within the human body in detail
    25. 25. DIGESTIVE SYSTEM Associated(accessory) organs
    26. 26. The PROCESS Mechanical Digestion Biting  Tearing  Slicing  Chewing (Masticating) Chemical Digestion  Acid  Enzymes
    27. 27. Mouth 1. Mechanical Digestion  Food is broken down into smaller pieces by the chewing, tearing, slicing and biting action of the teeth 2. Enzymatic Digestion  Starch is broken down into maltose by amylase in saliva  No digestion of proteins and fats in the mouth Starch  Maltose
    28. 28. Oesophagus Partially digested food is pushed down from the mouth into the stomach by muscles in the oesophagus that alternately contract and relax. (peristalsis) NO enzymes are present in the oesophagus.
    29. 29. Stomach Complex Proteins  Simpler Proteins Complex proteins are broken down into simpler proteins by proteases found in gastric juices secreted by the stomach. No digestion of carbohydrates or fats occur in the stomach.
    30. 30. Small Intestines Simpler Proteins  Amino Acids Maltose Glucose Fats  Glycerol + Fatty Acids Three digestive juices are secreted into the small intestines to complete digestion: 1. Bile from the Liver  This breaks fats into small droplets for easier digestion 2. Pancreatic Juice from the Pancreas  This contains carbohydrase, protease and lipase for digestion 3. Intestinal Juice from the Small Intestines  This also contains carbohydrase, protease and lipase.
    31. 31. Large Intestines Undigested food that reaches the large intestines will be passed to the rectum and anus for removal by the body as faeces. As it passes through, a lot of water is absorbed by the large intestines and taken back into the body.
    32. 32. INQUIRY time! Some obese people have had part of their small intestines removed. Suggest with reasons the effects of such a surgery? Proteins are digested in the stomach. The stomach wall consists of cells which are made of protein. So why does the stomach wall not get digested?
    33. 33. LEARNING OBJECTIVES You should now know how to: - identify the main organs in the human digestive system - explain the process of digestion within the human body
    34. 34. RECALLYou have learnt about• the meaning of digestion• why food must be digested• enzymes as biological catalysts that speed up the rate ofreactions without being chemically changed at the end ofthe reaction• the process of digestion and where specific nutrientsare digested in the body
    35. 35. Learning Objectives At the end of this lesson, you should be able to: • explain how digested food is absorbed into the bloodstream
    36. 36. ABSORPTION Small IntestineVillicells Blood Capillary
    37. 37. ABSORPTION Absorption is the movement of digested food molecules through the walls of the small intestine. By what process do the food moleculesSmall Intestine move through the intestinal walls? Why does food molecules move intoBlood Capillary the blood stream but not move out?
    38. 38. ABSORPTION Absorption is the movement of digested food molecules through the walls of the small intestine. Why are there so many finger-like projections in the cells of the smallSmall Intestine intestine?Blood Capillary
    39. 39. ABSORPTION Absorption is the movement of digested food molecules through the walls of the small intestine. Digested food molecules move through the walls of the small intestine via diffusion and active transport. Undigested food molecules are too large to move through the walls of the small intestine.Small Intestine Finger-like projections in the wall of the small intestine provide a large surface-area for absorption of digested food molecules.Blood Capillary
    40. 40. ABSORPTION 1. Finger-like projections in the wall of the small intestine provide a large How is the rate surface-area for absorption of digested of absorption food molecules. made faster in the small intestine?Small Intestine 2. The small intestine is long and convoluted, thus increasing the surface area for quicker absorption.Blood Capillary
    41. 41. ABSORPTION 3. The wall of the small intestine How is the rate is only one-cell thick, shortening of absorption the distance between the wall made faster in and blood vessels so absorption the small can be faster. intestine? 4. A constant flow of blood ensures a low concentration ofSmall Intestine food molecules in the capillary, so rate of diffusion of digested food molecules into the blood is increased.Blood Capillary
    42. 42. Learning Objectives At the end of this lesson, you should be able to: • explain how digested food is absorbed into the bloodstream
    43. 43. RECALLYou have learnt about• the meaning of digestion• why food must be digested• enzymes as biological catalysts that speed up the rate ofreactions without being chemically changed at the end ofthe reaction• the process of digestion and where specific nutrientsare digested in the body• how absorption occurs efficiently in the body

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