Question 120 marks
Question
(a) Beetroot is the large fleshy root of a beet plant. The cells of beetroot contain a coloured pigment. This pigment may leak from the cells if the cell membranes are damaged. You are going to investigate the effect of temperature on the leakage of pigment from beetroot cells. Read all the instructions but DO NOT CARRY THEM OUT until you have drawn a table for your results in the space provided in 1(a)(i). You should wear the gloves and eye protection provided during the practical work. Step 1 You are provided with two beetroot cylinders. Place each of these onto the white tile and use the scalpel to cut both cylinders to 3 cm in length. Step 2 Label one test-tube C and the other test-tube H. Place the test-tubes in the test-tube rack. Step 3 Put one beetroot cylinder into test-tube C. Step 4 Pour sufficient cold water into test-tube C so that the water level is just above the beetroot cylinder. Step 5 Raise your hand when you are ready for hot water to be put into the beaker labelled hot water. Step 6 Put one beetroot cylinder into test-tube H. Step 7 Pour sufficient hot water into test-tube H so that the water level is just above the beetroot cylinder. Step 8 Measure the temperature of the water in test-tube C and in test-tube H. Record these temperatures in your table in 1(a)(i). Step 9 Place a stopper in each test-tube. Step 10 Start the stop-clock. Leave the test-tubes for 10 minutes. Continue with the rest of the questions while you are waiting. Step 11 After 10 minutes shake both test-tubes for 5 seconds. Step 12 Remove the stopper from test-tube C. Pour the contents of test-tube C into an empty beaker. Use the forceps to remove the beetroot cylinder and place it on the white tile. Step 13 Pour the liquid in the beaker back into test-tube C. Step 14 Repeat steps 12 and 13 using test-tube H. Step 15 Observe the colour of the liquid in test-tube C and test-tube H. Record your observations in your table in 1(a)(i). (i) Prepare a table to record your results. [4] (ii) State a conclusion for these results. …… [1] (iii) In step 1 you were instructed to cut the beetroot cylinders to the same length. Suggest why this was necessary. …… [1] (iv) Identify one possible source of error in step 4 and step 7. Suggest a piece of apparatus that could be used to reduce this error. error …… apparatus …… [2] (v) Suggest the purpose of step 11. …… [1] (b) A student repeated the investigation in 1(a) at five different temperatures. They carried out three trials at each temperature. The student measured the percentage of light that passed through the liquids in the test-tubes. The coloured pigment reduces the percentage of light that can pass through the liquid. The higher the pigment concentration the less light passes through the liquid. The student’s results are shown in Table 1.1. Table 1.1 percentage of light that passes through the liquid temperature / °C trial 1 trial 2 trial 3 average 10 100 99 98 99 20 94 48 96 95 40 80 77 77 78 60 26 30 31 29 90 1 2 0 1 (i) State the variable that was changed (independent variable) in the investigation described in 1(b). …… [1] (ii) Suggest two ways in which the method described in 1(b) is an improvement on the method that you used in 1(a). 1 …… 2 …… [2] (iii) The student decided that the result for trial 2 at 20 °C was anomalous. State what is meant by an anomalous result. …… [1] (iv) State how the student dealt with the anomalous result when calculating the average value for 20 °C. …… [1] (v) Plot a line graph on the grid of the temperature against the average percentage of light that passes through the liquid using the data in Table 1.1. [4] (vi) Estimate the percentage of light passing through the liquid at 50 °C. Show on your graph how you obtained your estimate. ……% [2] [Total: 20]
Mark scheme
1(a)(i) 1 table drawn with header lines and at least 2 columns ; 3 2 headings with unit for temperature ; R units in data cells 3 recording of two correct temperatures and any 2 observations that correspond with the temperature ; 4 correct trend ; 1(a)(ii) more (pigment) is leaked at higher temperatures / AW ; ora 1 1(a)(iii) same, surface area / area of beetroot exposed to water / AW ; 1 ora same, number of cells / amount of pigment (of tissue at start) ; ora 1(a)(iv) error 2 volume (of water was not stated) / AW ; apparatus measuring cylinder / syringe / (graduated) pipette / burette ; OR error idea that temperature would change over time ; apparatus (named) insulating material / lid ; A (thermostatically) controlled water-bath error idea that timing of the samples would vary ; apparatus use separate stop clocks to time individually ; named correct equipment matching an error from a different step in the procedure ; 1(a)(v) idea of distribute colour evenly / mix ; 1 release more pigment ; 1(b)(i) temperature ; 1 1(b)(ii) wider range (of temperatures) ; ora 2 repeats ; ora A calculates an average / identifies anomalies ; ora measured light (that passes through liquid) ; ora A collects numerical / quantitative, data / not subjective 1(b)(iii) result that does not fit the pattern / does not fit with the other 1 results / not concordant / AW ; 1(b)(iv) did not include it (in the average) / AW ; 1 1(b)(v) Axes – labelled with units ; 4 Scale – suitable scale and plotted points occupies at least half the grid ; Plots – all points plotted accurately ± half a small square ; Lines – suitable line drawn ; 1(b)(vi) intersection on trendline at 50 °C shown ; 2 value from graph ;