Presentation on theme: "Chapter 5 Cell Activities"— Presentation transcript:
1 Chapter 5 Cell Activities 5.1 The Concept of Metabolism5.2 The Roles of Enzymes in Metabolism5.3 Factors Affecting Enzyme Activities5.4 Transporting Materials in and out of Cells
2 What is metabolism?All chemical activities taking place inside the body cells of an organism are collectively called metabolismExamples:Bone and wood: contain living cells carry out metabolismFinger nails and shells: truly dead materials no metabolism
5 Low metabolic rate at rest Metabolic rate = the overall speed of the chemical reactions in the organismsHigh metabolic rate when activeLow metabolic rate at rest
6 Why are enzymes so important? Catalysts: substances that speed up chemical reactionsEnzymes: catalysts which speed up chemical reactions inside the cellsEnzymes = biological catalystsEnzymesmaintain metabolic ratemay work inside or outside of the cells(e.g. digestive enzymes in the gut)
7 What are the properties of enzymes? Made up of proteinsSpeed up the rates of chemical reactionsAre regenerated / reused after reactionEffective in very small quantitiesEasily affected by changes in temperature and pHVery specific in the reactions they catalyse
8 Lock-and-key hypothesis How do enzymes work?Based on experimental evidence, scientists have proposed a hypothesis to explain how enzymes work and why enzymes are so specific in their actions:Lock-and-key hypothesisSubstrate : the reacting molecule in an enzyme-catalyzed reactionActive site : the particular site of the enzyme for reaction to occur; specific for each type of enzymeEnzyme-substrate complex : an unstable structure formed by the enzyme and substrate molecules during reaction
12 Practical 5.1 Investigating the presence of catalase in various plant and animal tissues IntroductionCatalase is an enzyme that speeds up the breakdown of hydrogen peroxide into water and oxygen. It is an example of catabolic reaction.ProcedurePrepare six boiling tubes in a holder.Add 5 cm3 hydrogen peroxide solution into each tube.Add a small piece of potato, apple, meat, liver and boiled liver of similar sizes into five of the tubes respectively. Do not add any tissues into the last tube.
13 Note whether any gas is evolved in each tube Note whether any gas is evolved in each tube. Test the gas with a glowing splint.Measure the highest point reached by the bubbles in each tube.
14 AnalysisWhat is the purpose of testing boiled liver?Ans: To show the effect of boiling on the activity of the enzyme catalyse in liverWhat is the purpose of doing the test in a test tube without any tissue?Ans: It acts as a control set-upCompare the results obtained. Give a conclusion for this experiment.Ans: Different tissues may contain different amounts of catalase so that they have different rates for the same reaction~ End of Practical 5.1 ~
15 Factors Affecting Enzyme Property of Enzyme:Protein has an active site with a particular three-dimensional shape maintained by weak bondingsUnder certain conditions:Breaking of weak bondingsChange in shape of the active siteAffect enzyme activity
16 How does temperature affect enzyme activity? Enzyme activity = the rate of substrate utilization or product formation
17 increase the rate of an enzyme-catalyzed reaction From 0 – 40/50CRise in temperature increase the rate of an enzyme-catalyzed reactionEffect of temperature on enzyme activity
18 Reasonsat higher temperature, the substrate molecules move fasterhigher chance for collision with the active siteshigher chance to form enzyme-substrate complexesgreater amount of product molecules
19 Reaction rate drops rapidly stops completely at 70 - 80C Above 50CReaction rate drops rapidly stops completely at CEffect of temperature on enzyme activity
20 Reasons at high temperature breaking of weak bondings change in shape of the enzymes and their active sites lose the catalytic activity enzyme is denatured
21 Around 0CVery low reaction rateReasonsmovement of the substrate molecules slow down at low temperaturethere is less chance for the substrate molecules to collide with enzyme moleculesenzyme is inactivated
22 Specific to different enzymes Lies around 45C for most enzymes Optimum temperatureThe temperature at which an enzyme-catalyzed reaction occurs most rapidlySpecific to different enzymesLies around 45C for most enzymesEffect of temperature on enzyme activity
23 How does pH affect enzyme activity? the degree of acidity or alkalinity of the reaction mediumSmall changes in pH greatly affect the enzyme activitiesEach enzyme has its optimum pHMost enzymes work best at pH 5 to 9, but some work best at an extreme pH
24 change in enzyme structure decrease in activity When pH optimum pHchange in enzyme structuredecrease in activityEffect of pH on enzyme activity
25 When there is drastic changes in pH denaturation of enzyme a great decrease in catalyzing abilityEffect of pH on enzyme activity
26 Critical Thinking 5.1 The optimum pHs of some enzymes The graph below shows the effect of pH on the activities of three different enzymes.
27 Questions1. Which enzyme works best in alkaline conditions?Ans: Trypsin2. Which enzyme works best in acidic conditions?Ans: Pepsin3. Which enzyme works best in neutral conditions?Ans: Salivary amylase4. What is the range of pH at which each enzyme is active?Ans:Pepsin: pH 1-3; salivary amylase: pH ; trypsin: pH
28 Practical 5.3 Investigating the effect of temperature on the activity of amylase IntroductionAmylase is a type of digestive enzyme found in saliva and the gut. It speeds up the breakdown of starch.In this experiment, we are going to test the effect of temperature on the activity of amylase.
29 ProcedurePrepare six water baths with the following temperatures: - 0C - room temperature - 40C - 60C - 80C - 100CPut 1 cm3 of amylase solution into each of six test tubes, and place them into the suitable water baths.Put 4 cm3 of starch solution into each of six other test tubes, and place them into the suitable water baths.
30 After 5 minutes, pour the amylase solution from a test tube into the starch solution in the test tube in the same water bath.After 10 minutes, pour 5 cm2 of Benedict’s solution to each tube and shake gently. Boil for 5 minutes.6. Shake the tubes at 1-minutes intervals. Note the colour changes of the mixtures. Compare the amount of brick-red precipitate formed in the six tubes.
32 AnalysisWhat is the purpose to keep the test tubes containing the starch solution and amylase solution in each water baths for about five minutes before mixing?Ans: To ensure that both starch and amylase solutions have reached the desired temperatures before mixing2. What is the optimum temperature for the action of amylase?Ans: At 60C4. Explain the effect of temperature on the activity of amylase.Ans: Amylase is inactive at 0C. The rate of reaction increases steadily with temperature, and reaches the maximum at the optimum temperature of 60C. Beyond the optimum temperature, the reaction rate drops rapidly and finally stops completely due to denaturation of enzyme
33 Practical 5.4 Investigating the effect of pH on the activity of amylase IntroductionIn this experiment, we are going to test the effect of pH on enzyme activity. Amylase is extracted from mung beans for the test.
34 ProcedureSoak 10 mung beans in water for two days.Remove the seed coat. Grind them with 2 cm3 of distilled water.
35 Filter the mixture and collect the filtrate in a test tube.
36 Prepare and label six cavities of a spot tile as follows: A: Amylase extract + 1 drop of distilled waterB: Dilute hydrochloric acid (HCl)C: Amylase extract + 1 drop of dilute HClD: Dilute sodium bicarbonate solution (NaHCO3)E: Amylase extract + 1 drop of dilute NaHCO3F: Distilled waterABCEDF
37 Prepare six small filter paper discs. Put one filter paper disc into each of cavities A to F.ABCEDF
38 Drain away excess liquid from the paper discs, and put them onto a starch-agar plate. Incubate the starch-agar plate at 40C for half an hour.
39 Remove the paper discs from the plate Remove the paper discs from the plate. Flood it with iodine solution for 1 minute and then flush gently with tap water.Observe the colour changes.
40 Ans: They act as control set-ups AnalysisWhy do we carry out the tests for the liquids in the cavities A, C and E in the spot tile?Ans: To investigate the amylase activity at neutral, acidic and alkaline conditions respectivelyWhy do we carry out the tests for the liquids in cavities B, D and F in the spot tile?Ans: They act as control set-ups3. Why do we incubate the agar plate at 40C instead of room temperature?Ans: It provides an optimum temperature for most enzyme-catalyzed reactionsIn which medium does amylase work best?Ans: In an alkaline mediumFrom the results, give a conclusion for this experiment.Ans: Amylase works best in an alkaline medium~ End of Practical 5.4 ~
41 Practical 5.5 Comparing the protease activities in different fruit juices IntroductionIn some fruit juices, there are enzymes that can break down proteins.We will use a milk-agar plate to compare the protease activities of different types of fruits.
42 ProcedurePrepare a milk-agar plate.Prepare a small amount of juice from each of several types of fruits (e.g. pineapple, kiwi fruit, papaya, guava and mango) by using a mortar and a pestle.Collect the filtrate and dilute with distilled water (2cm3 of filtrate with 8cm3 distilled water).
43 Remove 6 circular discs of agar from the agar plate. Fill a well in the milk-agar with two drops of a fruit juice.Incubate the plate at 40C for 1 to 2 hours.Note and measure the diameter of the clear zone around each well.
44 AnalysisSuggest a sample for the control experiment.Ans: Distilled waterHow are the clear zones formed in the milk agar?Ans: In some fruits, there are enzymes (proteases) that can break down proteins. If the milk protein in the milk-agar plate is digested, a clear zone will appear in the agar plate3. What is the relationship between the diameter of the clear zone and protease activity?Ans: The higher the protease activities, the larger the diameter of the clear zone
45 Further Investigation You may do a similar experiment to compare or study the protease activities of the following solutions:biological washing powder,meat tenderizer,protein-removal tablets for contact lenses.~ End of Practical 5.5 ~
46 Enrichment Reading 5.1Making use of enzymes in everyday lifeQuestions for DiscussionWhy are commercial enzymes mainly obtained from microorganisms?Ans: It is because the reproductive rate of microorganisms is fast and the yield of commercial enzymes is high2. Why is it possible to obtain maltose from starch?Ans: Starch is converted to maltose by amylase
47 3. Why can proteases be used to make meat more tender? Ans: Proteases partially break down proteins in the meat tissues that are originally responsible for its tough nature4. Why can proteases be used to remove egg stains and blood stains from clothes?Ans: Proteases can break down the proteins present in egg stains and blood stains~ End of Enrichment Reading 5.1 ~
48 Activities of the cellVarious substancesCellsWaste productCarry out various life processes, such asreleasing energybuilding up cellular structuressupplied toremoved from
49 Cell membraneHas many tiny poresSelectively permeableAllows some particles to pass through but not othersProcesses involved in transport of materialsDiffusionOsmosisActive transport
50 What is diffusion?The net movement of the particles of a substance from a region of higher concentration to a region of lower concentrationThe net movement continues until the concentration of the substance in the two regions are the sameIt is a passive process
51 Concentration gradient The difference in concentration between two regions where diffusion occursDetermines the rate and the direction of diffusion
52 Critical Thinking 5.2 The diffusion of ink in water A small amount of blue ink was put in a beaker containing water. The photographs below show the colour change of the water immediately, 10 minutes later and 20 minutes later.
53 Questions1. How does the colour of the water change within 20 minutes?Ans: The blue colour spreads out gradually in water2. Explain the colour change.Ans: Ink particles spread from a region of high concentration to a region of low concentration by diffusion
54 Questions3. What do you expect to see if the solution is allowed to stand for a long time? Are the ink particles still moving at this state?Ans: The water will become blue evenly; ink particles are still moving randomly4. Will the result be different if the demonstration is carried out at a higher temperature? Why?Ans: The blue colour will spread out much faster, because the ink particles possess more kinetic energy
55 What factors affect the rate of diffusion? Molecular size – Small particles diffuse faster than larger particlesConcentration gradient / difference – Diffusion occurs more rapidly if there is a larger difference in concentration between two regionsDistance of diffusion – Diffusion occurs more slowly if the distance betweem the two regions is longer
56 Surface area –. For substances diffusing through a membrane, Surface area – For substances diffusing through a membrane, a larger surface area promotes a faster rate of diffusionTemperature – Diffusion occurs more rapidly with a rise in temperature (because the kinetic energy of particles increases)
57 Why is diffusion important to organisms? It is important in the exchange of useful and wasteful substances between:cells and body fluidsthe organism and its surroundingsExamples:Gas exchange in the breathing organs of animalsGas exchange on the leaf and stem surfaces of plantsAbsorption of digested food in the small intestine
58 What is osmosis?Osmosis refers to the diffusion of water from the dilute solution to the concentrated solution across a selectively permeable membrane
59 Why does osmosis occur?What will happen when a concentrated sucrose solution is separated from a dilute sucrose solution by a selectively permeable membrane?Note:The membrane has numerous tiny pores that allow small particles (e.g. water molecules) to pass through, but not larger particles (e.g. sucrose molecules)
60 Region B contains a higher proportion of sucrose molecules and a lower proportion of freely moving water moleculesIn a sucrose solution, the sucrose molecules and water molecules are in continuous, random motion
61 Only water molecules can pass through the membrane in both directions and more pass from region A to region BThere is a net movement of water molecules from dilute to concentrated solution across the membrane
62 Osmosis is a special type of diffusion Takes place only when a selectively permeable membrane is presentDefinition: the diffusion of water molecules from a dilute solution to a more concentrated solution across a selectively permeable membrane
63 What is water potential? Water potential is the total energy for the water molecules in a solution to move aboutNet movement of water molecules: from a region of higher water potential to a region of lower water potentialPure water has the highest water potential, its water potential is defined as zeroWhen substances are dissolved in water, water potential become less than zeroConcentrated sucrose solution has a lower water potential than dilute sucrose solution
64 How does osmosis affect organisms? Water molecules may move into or out of the cell by osmosis depending on the concentration of substances dissolved in the fluid around a cell3 terms to describe the relative concentration of solutions:HypertonicHypotonicIsotonic
65 Hypertonic solutionA solution with a water potential lower than that of another solution, e.g. the water potential of the solution in the cellWhen animal cells are placed in a hypertonic solution: water leaves the cell by osmosis shrinkingWhen plant cells are placed in hypertonic solution: water leaves the cell by osmosis shrinking of cytoplasmcytoplasm becomes separated from cell wall (i.e cell is plasmolysed)plant tissue becomes flaccid
66 Red blood cells shrink (4 000) Plant cells become plasmolysed
67 Hypotonic solutionA solution with a water potential higher than that of another solution, e.g. the water potential of the solution in the cellWhen animal cells are placed in hypotonic solution: water enters the cell by osmosis expand or even burstWhen plant cells are placed in hypotonic solution: expand, but swelling is limited by the cell wall become turgid
68 Red blood cells swell (4 000) Plant cells become turgid
69 Isotonic solutionA solution with the same water potential as that of another solutions, e.g. the water potential of the solution in the cellImportant to maintain a suitable water potential of body fluids (e.g. the blood)
70 The cell shrinks and becomes plamolysed Water leaves the cellThe cell shrinks and becomes plamolysedNo net movement of water into or out of the cellImmersed in hypertonic solutionImmersed in isotonic solutionImmersed in hypotonic solutionWater enters the cellThe cell swells and becomes turgidA plant cell
71 The cell swells and eventually burst The cell shrinks An animal cellImmersed in hypertonic solutionImmersed in hypotonic solutionWater enters the cellWater leaves the cellImmersed in isotonic solutionNo net movement of water into or out of the cell
72 Importance of osmosis to plants For water absorption- water potential of the root epidermal cells is lower than that of soil water- water moves from the soil (higher water potential) into the root epidermal cells (lower water potential)For support- young, non-woody plants depend entirely on turgidity for support- if water loss is significant, plant tissue will become flaccid and the plant will wilt
73 Practical 5.6 Studying osmosis by using a dialysis tubing IntroductionThe phenomenon of osmosis can be demonstrated by:using a selectively permeable membraneusing two solutions of different concentrations
74 ProcedureSoak a dialysis tubing in water.Open up and tie a knot close to one end of the dialysis tubing.Fill the dialysis tubing with 20% sucrose solution.Tie the other end of the dialysis tubing to a 1 cm3 pipette.Wash the dialysis tubing with distilled water.Place the dialysis tubing into a beaker of distilled water.Measure & record the change in liquid level.Set up a control.
75 1. Why do we rinse the outer surface of the dialysis tubing? Analysis1. Why do we rinse the outer surface of the dialysis tubing?Ans: To avoid introducing sucrose solution to the surrounding medium2. How does the volume of sucrose solution in the dialysis tubing change with time?Ans: It rises with time, indicating that the volume of sucrose solution in the dialysis tubing increases3. Explain the result of this demonstration.Ans: There is a net movement of water molecules into the sucrose solution from surrounding through the selectively permeable membrane by osmosis~ End of Practical 5.6 ~
76 Practical 5.7 Studying osmosis in a living plant tissue IntroductionInstead of using a dialysis tubing, a living tissue (potatoes) can be used to demonstrate osmosis.
77 ProcedurePeel off the skins of potatoes and make 3 potato cups.
78 2. Place the potato cups into three petri dishes containing distilled water, and label as: - A (unboiled, cavity filled with distilled water)- B (unboiled, cavity filled with sucrose solution)- C (boiled, cavity filled with sucrose solution)Observe the change in the level of the solution in each potato cup 24 hours later.
79 Analysis1. Describe your observation.Ans:There is an increase in the liquid level in B.The liquid level remains more or less unchanged in A.The level of the sucrose solution in C drops until it is equal to the level of distilled water outside.
80 2. Explain the changes in liquid level in A, B and C. Ans: A: no osmosis occurs, because there is no concentration difference between distilled water in the cavity and that in the petri dish;B: osmosis occurs, because distilled water has a higher water potential than that of the sucrose solution. Water molecules diffuse across potato cells into the cavity;C: no osmosis occurs, because strong heat kills the potato cells and destroys their cell membrane which become freely permeable. The sucrose solution moves out of the cavity until its level is equal to the level of water outside
81 3. At the end of the experiment, in which set-up, B or C, may we find sucrose in the water outside the potato cup? Explain briefly.Ans: We may find sucrose in the water outside the potato cup in set-up C because the cell membrane of potato cells in C become freely permeable after strong heating. Thus, the sucrose molecules move out of the cell into the distilled water outside.~ End of Practical 5.7 ~
82 What is active transport? It is need, for instance, to transport substances against a concentration gradientIt is a process of transporting substances across the cell membrane with the use of energyIt can only take place in living cellsIt involves carriers (special protein molecules) located on the cell membrane
83 The action of the carrier protein in active transport Low concentration outside the cellSubstance to be transportedMovement of substances against the concentration gradientCarrier moleculeCell membraneHigh concentration inside the cell1. The substance enters the carrier molecule2. The carrier molecule combines with the substance and changes its shape. The energy needed for this comes from respirationThe action of the carrier protein in active transport3. The change of shape of the carrier molecule releases the substance into the cell
84 Why is active transport important to organisms? Enables a cell to take in useful substances / remove waste substances against the concentration gradientAllows the transport of substances across the membrane when:- diffusion is too slow- there is no concentration gradient
85 Examples:In the human body:Absorption of glucose by the cells lining the small intestineAbsorption of minerals by the cells lining the kidney tubulesIn plants:Absorption of minerals from the soil