Chapter 4: Chemical Composition of the Cell

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Experiment for biology form 4 chapter 4

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Chapter 4: Chemical Composition of the Cell

  1. 1. Biology |Form 4 | Chapter 4: Chemical Composition in Cell 10Activity 4.1Aim To differentiate between reducing and non-reducing sugars.Materials 5% glucose solution, 5% fructose solution, 5% galactose solution, 5% maltose solution, 5% lactose solution, 5% sucrose solution, dilutehydrochloric acid, water, sodium hydrogen carbonate powder and Benedict’s solutionApparatus Test tubes, beaker, Bunsen burner, tripod stand, wire gauze and test tube holderA.Testing for reducing sugarsProcedure1. 2 ml of Benedict’s solution are added to 2 ml of glucose solution in a test tube2. The test tube is placed in a water bath of boiling water for 5 minutes.3. The colour of the precipitate that is formed (if any) is recorded in the table below.4. Steps 1 to 3 are repeated for all the other sugar solutions.Results Sugar solution Benedict’s solution Sugar solution Benedict’s solutionGlucose Brick-red precipitate Maltose Brick-red precipitateFructose Brick-red precipitate Lactose Brick-red precipitateGalactose Brick-red precipitate Sucrose Blue solutionDiscussion 1. Glucose, fructose, galactose, maltose and lactose are reducing sugars because they give a positive Benedict’s test.2. Sucrose is a non-reducing sugar because it gives a negative Benedict’s test.B.Testing for non-reducing sugarProcedure 1. 2 ml of sucrose solution and 1 ml of dilute hydrochloric acid are added to a test tube2. The test tube is placed in a water bath and boiled for 5 minutes.3. The test tube is cooled under a tap and sodium hydrogen carbonate powder is added to neutralize the excess acid.4. When it stops fizzing, 2 ml of Benedict’s solution are added to the mixture in the test tube。5. The test tube is placed in the water in the water bath again and boiled for 5 minutes.Observation A brick red precipitate is formed in the test tube.
  2. 2. Biology |Form 4 | Chapter 4: Chemical Composition in Cell 11Discussion 1. Sucrose is hydrolysed into glucose and fructose by boiling the sucrose solution with dilute hydrochloride acid.2. When the solution containing glucose and fructose is boiled with Benedict’s solution, it produces a brick-red precipitate.Conclusion Glucose, fructose, maltose are reducing sugars. Sucrose is non-reducing sugar.
  3. 3. Biology |Form 4 | Chapter 4: Chemical Composition in Cell 12Experiment 4.1Aim To study the effects of temperature on the activity of salivary amylase.Problem statement What are the effects of temperature on the activity of salivary amylase?Hypothesis The optimum temperature for salivary amylase is 37oC.Variables (a) Manipulated variable: Temperature(b) Responding variable: Rate of reaction(c) Fixed variable: Volume and concentration of starch suspension, volume and concentration of saliva suspension, pH of starch andsaliva suspensions.Apparatus Beakers, test tubes, tripod stand, wire gauze, Bunsen burner, thermometer, dropper, glass rod, syringes, stopwatch, spotting tile and testtube rackMaterials 1% starch starch suspension, saliva, iodine solution, ice cubes and distilled waterTechnique Recording the time taken for the complete hydrolysis of starch with a stopwatch. The presence of starch is indicated by the iodine test.
  4. 4. Biology |Form 4 | Chapter 4: Chemical Composition in Cell 13Procedure1. The mouth is rinsed with distilled water.2. The saliva suspension is prepared by spitting into a small beaker and diluting the saliva with an amount of distilled water equal tothe amount of saliva.3. Five water baths are prepared at the following temperatures: 0oC, 20 oC, 37 oC, 50 oC and 60 oC.4. Two test tubes are labelled P and Q.5. 4 ml of starch suspension are placed in test tube P and 1 ml of saliva suspension in test tube Q.6. Both test tubes are placed into the first water bath (at 60 oC) for 5 minutes.7. A drop of iodine solution is placed into each groove of a clean spotting tile.8. A drop of suspension from test tube P is poured into the saliva suspension in test tube Q. The stopwatch is started immediately.9. A drop of suspension is taken out from the test tube Q every minute and tested with iodine solution on the spotting tile.10. Test tube Q is kept in the water bath thoughout the experiment.11. The time taken for the complete hydrolysis of starch is recorded in the table, that is, when the iodine solution does not turn blueanymore..
  5. 5. Biology |Form 4 | Chapter 4: Chemical Composition in Cell 1412. Steps 4 to 9 are repeated for temperatures 20 oC, 37 oC, 50 oC and 60 oC.13. The results are recorded in the table below.14. A graph of rate of reaction against temperature (oC) is plotted.ResultsTemperature of waterbath (oC)Time taken for completehydrolysis of starch, t (minute)Rate of reaction,(minute-1)0 >30 <0.0320 8 0.1337 0.33 350 6 0.1760 >30. <0.03Discussion 1. The test tubes P and Q are kept in the water bath for 5 minutes to stabilize the temperature of the suspensions in the two test tubes.2. When the amylase in the saliva has completely hydrolysed the starch, the dark blue colour does not form in the iodine test.3. At low temperatures, the reaction progresses slowly. As the temperature increases, the rate of reaction increases until the optimumtemperature of 37oC is reached. Above the optimum temperature, the rate of reaction falls rapidly.Conclusion The rate of reaction is highest at the temperature 37oC. the hypothesis is accepted.
  6. 6. Biology |Form 4 | Chapter 4: Chemical Composition in Cell 15Experiment 4.2Aim To study the effects of pH on the activity of pepsin.Problem statement What are the effects of pH on the activity of pepsin?Hypothesis The enzyme pepsin works best in acidic conditions.Variables (a) Manipulated variable: pH of medium(b) Responding variable: Rate of reaction(c) Fixed variable: Volume and concentration of egg albumen suspension, volume and concentration of pepsin solution, temperature ofmediumMaterials Egg albumen suspension, dilute hydrochloride acid, dilute sodium hydroxide solution, 1% of pepsin solution, pH paper and distilledwaterApparatus Beaker, tripod stand, wire gauze, Bunsen burner, thermometer, dropper, test tubes, test tube rack and syringesProcedure1. The egg albumen suspension is prepared by adding 1g of dried egg albumen to 100 cm3of water. The mixture is then heated to90oC.2. Three test tubes are labelled P,Q and R.3. 5 ml of egg albumen suspension and 1 ml of pepsin solution are placed in each test tube.4. 5 drops of distilled water are added to test tube P.5. 5 drops of dilute hydrochloric acid are added to test tube Q.6. 5 drops of dilute sodium hydroxide solution are added to test tube R.7. All the three test tubes are placed into a water bath at 37oC for 20 minutes.8. The appearance of the contents in each test tube is recorded at the beginning and the end of the experiment.9. The contents in each test tube are tested with pH paper.10. The results are recorded in a table.
  7. 7. Biology |Form 4 | Chapter 4: Chemical Composition in Cell 16Results TesttubepH ContentsAppearance of contentsAt the beginning of the experiment At the end of the experimentP 7 Albumen + pepsin + distilled water White suspension White suspensionQ 2Albumen + pepsin + dilutehydrochloric acidWhite suspension Clear solutionR 9Albumen + pepsin + dilute sodiumhydroxide solutionWhite suspension White suspensionDiscussion 1. The test tubes are kept in a water bath maintained at 37oC because that is the optimum temperature for pepsin.2. The mixture in test tube Q is clear at the end of the experiment because the albumen has been hydrolysed.3. Pepsin does not catalyse the hydrolysis of albumen in the neutral and in alkaline conditions.Conclusion Pepsin catalyses the hydrolysis of protein only in acidic conditions. The hypothesis is accepted.
  8. 8. Biology |Form 4 | Chapter 4: Chemical Composition in Cell 17Experiment 4.3Aim To study the effects of substrate concentration on salivary amylase activity.Problem statement What are the effects of substrate concentration on salivary amylase activity?Hypothesis The rate of enzymatic reaction increases with the increase in substrate concentration until it reaches a maximum rate.Variables (a) Manipulated variable: Substrate concentration(b) Responding variable: Rate of concentration(c) Fixed variable: Enzyme concentration, temperature, pH of starch and saliva suspension, volume of starch and saliva suspensionMaterials 0.1%, 0.2%, 0.3%, 0.4%, 0.5% and 0.6% starch suspensions, saliva, iodine solution and distilled waterApparatus Beakers, test tubes, tripod stand, wire gauze, Bunsen burner, thermometer, dropper, glass rod, syringes, stopwatch, spotting tile and testtube rackTechnique Recording the time taken for the complete hydrolysis of starch with a stopwatch. The presence of starch is indicated by the iodine test.Procedure 1. The mouth is rinsed with distilled water.2. The saliva suspension is prepared by spitting into a small beaker and diluting the saliva with an amount of distilled water is equal tothe amount of saliva.3. Six test tubes are labelled P, Q, R, S, T and Uare filled with the following starch suspensions using different syringe.Test tube Type of starch suspensionP 4 ml 0.1% starch suspensionQ 4 ml 0.2% starch suspensionR 4 ml 0.3% starch suspensionS 4 ml 0.4% starch suspensionT 4 ml 0.5% starch suspensionU 4 ml 0.6% starch suspension4. 1 ml of saliva suspension is placed in a test tube.5. A drop of iodine solution is placed into each groove of a clean spotting tile.6. Test tube P and the test tube containing the saliva suspension are placed into a water bath at 37oC.7. After 5 minutes, the saliva suspension is poured into the starch suspension in test tube P. the stopwatch is started immediately.8. A drop of suspension is taken from test tube P every minute and tested with iodine solution on the spotting tile.9. Test tube P is kept in the water bath throughout the experiment.10. The time taken for the complete hydrolysis of starch is recorded in the table, that is, when the iodine solution does not turn blueanymore.11. Steps 4 to 10 are repeated for test tubes Q, R, S, T and U.12. The results are recorded in the table below.13. The graph of rate of reaction (% minute-1) against concentration of starch suspension (%) is plotted.
  9. 9. Biology |Form 4 | Chapter 4: Chemical Composition in Cell 18Results Concentration of starchsuspension, C (%)Time taken for the complete hydrolysis of starch,t Rate of reaction = C/t(% minute-1)(seconds) (minutes)0.1 300 5.00 0.020.2 300 5.00 0.040.3 300 5.00 0.060.4 300 5.00 0.080.5 375 6.25 0.080.6 450 7.50 0.08Discussion 1. The rate of reaction increases with the increase in the concentration of the substrate (starch) concentration, that is from 0.1% to0.4% starch suspension.2. The maximum rate is reached at 0.4% starch suspension. At this point all the active sites of the enzymes are filled at anyone onetime. This is referred to as saturated point.3. Beyond the saturation point, the rate of reaction does not increases even through the substrate concentration is increased because theconcentration of enzyme becomes a limiting concentration.Conclusion The rate of enzymatic reaction increases with the increase in substrate concentration until it reaches a maximum rate. The hypothesis isaccepted.

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