Aqa As Required Practicals Methods Questions And Mark Schemes-Books Pdf

AQA AS Required Practicals Methods Questions and Mark Schemes
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A level Biology required practical No 1, Student Sheet. Investigation into the effect of a named variable on the rate of an enzyme controlled reaction. The effect of temperature on the rate of the reaction catalysed by trypsin. Casein is a protein found in milk Trypsin is an enzyme that digests casein When trypsin is added to a. dilute solution of milk powder the casein is digested and the solution goes clear. You are provided with the following, 0 5 trypsin solution. 3 solution of milk powder, pH7 buffer solution, a large beaker to use as a water bath. test tubes, test tube rack, stop watch, marker pen. pipettes or syringes, thermometer, You are required to find the rate of reaction at five different temperatures.
You should read these instructions carefully before you start work. 1 Using a marker pen write an X on the glass halfway down one side of each of three test tubes. 2 Add 10 cm3 of the solution of milk powder to each of these three test tubes. 3 Add 2 cm3 of trypsin solution to 2 cm 3 of pH 7 buffer in another set of three test tubes. 4 Stand the three test tubes containing the solution of milk powder and the three test tubes containing. trypsin and buffer in a water bath at 20 oC, 5 Leave all six tubes in the water bath for 10 minutes. 6 Add the trypsin and buffer solution from one test tube to the solution of milk powder in another test tube. and mix thoroughly, 7 Put the test tube back into the water bath. 8 Repeat steps 6 and 7 using the other test tubes you set up. 9 Time how long it takes for the milk to go clear Do this by measuring the time taken to first see the X. through the solution, 10 Record the time for each of the three experiments. 11 Using the same method find out how long it takes the trypsin to digest the protein in the solution of milk. powder at 30 oC 40 oC 50 oC 60 oC, 12 Record your data in a suitable table. 13 Process your data and draw a graph of your processed data. Alternative method using colorimeter, 5 Leave all six tubes in the water bath for 10 minutes While you are waiting set up a colorimeter Use.
the trypsin solution as a blank to calibrate the colorimeter to zero absorbance. 6 Add the trypsin and buffer solution from one test tube to the solution of milk powder in another test tube. and mix thoroughly, 7 Put the test tube back into the water bath Time the reaction for exactly 4 minutes Pour the contents. of the tube into a cuvette and measure the absorbance immediately. 8 Repeat steps 6 and 7 using the other test tubes you set up. 9 Record the absorbance for each of the three experiments. Questions on the practical, 1 a What is your independent variable. b What is the range of your independent variable, c When the technicians made up the trypsin and milk powder solutions before the experiment they. decided to make up the solutions in one large batch rather than weighing out the trypsin and milk. powders for each group separately Would their method result in more or less accurate dilutions. explain your answer, c What is your dependent variable. d What are your control variables and how did you control them. e Why are all the test tubes left in the waterbaths for 10 minutes before the trypsin and milk are added. 2 Why does the risk assessment for this practical instruct you to wear safety goggles and gloves. 3 Why did the milk become clearer in this investigation. 4 There are two possible ways of measuring the dependent variable in this particular method. a One method involves timing how long it takes for a cross to become visible through the milk What. are the limitations of this method, b The other method involves using a colorimeter to measure the absorbance of the mixture after.
exactly four minutes, i What is a cuvette and how should they be handled carefully. ii Why is it necessary to use a blank in the colorimeter. iii Why does the absorbance of the mixture change after the milk and enzyme solutions are. mixed together, iv Why are you told to take a reading of absorbance immediately you add the mixture to the. cuvette after 4 minutes, v Why is using a colorimeter likely to give more accurate results than the first method. 5 Describe the pattern of results that you obtained. 6 What is the optimum temperature for this trypsin enzyme what additional readings do you need to. take to identify this temperature with greater accuracy. 7 Explain the pattern of results using A Level enzyme science make sure you include why the rate. of breakdown increases as temperature increases up to the optimum why the rate decreases as. the temperature increases above the optimum, ISA Questions. 1 You used a buffer solution in your investigation What are buffer solutions used for 1 mark. 2 You left the test tubes in the water bath for 10 minutes before you added the enzyme to the milk. powder solution Explain why 1 mark, 3 Did you use a water bath at room temperature Give a reason for your answer 1 mark.
4 Describe and explain what you did to make sure the temperatures of the waterbaths were as. reliable as possible 2 marks, 5 Explain why you set up three experiments at each temperature 2 marks. 6 A student decided to improve this investigation with control experiments At each temperature she. set up a test tube containing a solution of milk powder and buffer She did not add trypsin What. would these control experiment show 1 mark, 7 8 It is difficult to decide when the milk solution goes clear Suggest one better way of determining. when the milk solution goes clear 2 marks, ISA Markscheme. 1 Maintain constant pH 1, 2 To equilibrate reach temperature at which reaction will take place 1. 3 Credit yes only together with valid reason temperature variation greater in air than in water room. air temperature may fluctuate water bath keeps test tubes at constant temperature 1. 4 Measure temperature of water bath at beginning and end of reaction period as a minimum number. To assess the effect of any temperature changes during the reaction to show that there was no little. variation in temperature, Measure temperature several times and add hot or cold water as appropriate.
To try to keep the temperature close to that required 2. 5 Enables calculation of a more reliable mean, So that anomalous data can be identified 2. 6 Controls show that the casein digested was due to the action of enzyme not due to temperature. 8 Use a colorimeter, Record time taken to reach constant set value of absorbance transmission. Set up a standard solution where complete digestion has occurred for comparison. Measure the time taken to reach same colour transparency as standard 2. Another Enzyme practical from an ISA Catalase on piece of card Questions. Calculate the mean time taken for the card to rise to the surface at each concentration of hydrogen. peroxide 1 mark, Use the graph paper provided to plot a graph of your processed data Write a suitable title for. your graph 6 marks, 1 You were told to remove the card from the catalase extract and shake off any surplus. liquid step 3 Explain why it is necessary to shake off surplus liquid 2 marks. 2 It would have been better if you had kept temperature and pH constant in this. investigation, 2 a Describe how you could keep temperature constant 2 marks.
2 b Describe how you could keep pH constant 1 mark. 3 You were told to repeat the measurements at each concentration of hydrogen. peroxide step 7, How many repeats did you carry out at a concentration of 100 hydrogen peroxide. Explain why you carried out this number of repeats. Number of repeats, Explanation 1 mark, 4 In this investigation you found the time taken for the card to rise to the surface. Explain why this is a valid measure of the rate of the reaction 3 marks. 5 Another student carried out the same investigation as you did She obtained the. results shown in the graph, 1 time in seconds, the surface as. Rate at which, card rose to, 0 20 40 60 80 100 120. Percentage concentration of hydrogen peroxide, 5 a Describe the results that the student obtained 2 marks.
5 b What factor limited the rate of reaction between hydrogen peroxide concentrations of. 0 and 30 Give the evidence for your answer, Evidence 2 marks. 6 A student carried out a similar investigation to yours He decided to carry out repeats. using the same piece of card in the same tube Each time the card reached the. surface he immediately pushed it back down again He noticed that the card took. longer to return to the surface each time Explain why the card took longer to return. to the surface 2 marks, Markscheme, 1 1 Liquid contains enzyme. 2 Need to add same amount of enzyme each time extra enzyme may increase rate of reaction. extra enzyme may affect rate of reaction, 2 A 1 Water bath. 2 Monitor temperature with thermometer use data logger to record temperature. 3 Adjust temperature with hot cold water, 2 max The basic principles are. 1 using a water bath and 2 describing how the temperature is monitored. These points should be marked independently, 2 b Use buffer.
3 One repeat because readings very similar concordant. Two or more because first repeat not concordant variation in values so that anomalies can. be identified so that mean is more reliable, 4 1 Bubbles oxygen make card rise. 2 The faster the rate of reaction the greater the amount of oxygen. 3 The faster the rate of reaction the more bubbles oxygen on card. 4 The faster the rate of reaction the quicker the card will rise to the surface. 5 A 1 Rate increases then remains constant, 2 At concentration of 42 at rate of 0 045. 5b 1 Concentration of hydrogen peroxide substrate percentage. concentration, 2 As concentration increases so does the rate at which card. rose of reaction positive, correlation between, concentration and rate at which. card rose of reaction, Alternative Investigation the Effect of pH on the rate of protein digestion by a protease.
A student set up boiling tubes containing 2cm 3 of protease and 5cm3 of buffer solution of differing pHs. A glass capillary tube containing solidified egg white the protein albumin was placed in each tube. The length of the egg white in the tubes was measured before being placed in the solutions The. boiling tubes were stoppered and placed in a water bath for 12 hours at 30 oC After this time the. capillary tubes were removed and the lengths of the egg whites remaining were measured. pH Initial length of egg Final length of egg 1 Why is it important to calculate. white in tube mm white in tube mm of egg white digested rather than simply change. 4 8 52 48 length of egg white in mm, 5 8 50 45 2 Suggest a suitable control for this. 6 6 54 32 investigation nb this is not the same as a. 7 6 53 9 control variable Explain why a control is. 8 6 48 25 needed, 9 0 52 38 3 Why are the boiling tubes. 9 6 54 47 stoppered before being placed in the water. 4 Why are buffer solutions used in this investigation rather than just adding the correct volume of. an acid or alkali to produce the correct pH at the start of the investigation think about what is. produced as the protein is digested, 5 One student concluded that the optimum pH for this enzyme is 7 6 Do you agree with this. conclusion explain your answer, 6 Use your knowledge of enzyme science to explain the results of the investigation. A level Biology required practical No 2, Student Sheet.
Preparation of stained squashes of cells from plant root tips set up and use of and optical. microscope to identify the stages of mitosis in these stained squashes and calculation of a mitotic. Root tip squash using onion root meristem tissue, You are provided with the following. 100 ml beaker, hydrochloric acid 5 mol dm 3, microscope slide and cover slip. toluidene blue stain, filter paper, mounted needle. distilled water, watch glass, root tip of onion or garlic. microscope and light source, You are required to prepare a microscope slide of the meristem tissue from an onion root You will add a.
stain to the material which allows you to see the chromosomes You will look at the slide under the. microscope to identify any cells showing stages of mitosis You will then calculate the mitotic index. Hydrochloric acid 5 mol dm 3 is corrosive and should be handled with caution. Eye protection must be worn, The beaker must be stood on a bench mat Do not carry the beaker with acid in. N B Do not leave root tips for investigation lying about on the bench top prior to staining Cut your root tip. immediately before you put it into the acid This will stop any reactions and hopefully some cells will be in a. stage of division, You should read these instructions carefully before you start work. Making your slide, 1 Stand the beaker on a bench mat before adding approx 10ml of hydrochloric acid 5 mol dm 3. 2 Place about 2 cm of root tip in the acid and leave for 15 minutes. 3 Set up your microscope while you are waiting, 4 Rinse the root tip in distilled water in the watch glass. 5 Cut off the root tip 1mm and place on a microscope slide. 6 Cover the section with toluidene blue stain and macerate with the mounted needle to separate the cells. 7 Continue to macerate until the tissue is well broken and the cells are stained dark blue. 8 Add a cover slip and with gentle finger pressure spread the material and blot at the same time by using. a folded filter paper between finger and slide, 9 L.
A Level Biology AQA OCR Edexcel Required Practical Methods Questions and Mark Schemes Name Total Marks A level Biology required practical No 1 Student Sheet Investigation into the effect of a named variable on the rate of an enzyme controlled reaction The effect of temperature on the rate of the reaction catalysed by trypsin Casein is a protein found in milk Trypsin is an enzyme that

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