Biology 0610/62 February/March 2021: question paper and mark scheme

Question

A student investigated osmosis. They used a model cell made from dialysis tubing. Dialysis tubing is permeable to water but is not permeable to larger molecules such as sucrose, which is a type of sugar. Step 1 One test-tube was labelled DW and a second test-tube was labelled S. Step 2 Two dialysis tubing bags were made by knotting lengths of dialysis tubing at one end. Step 3 A syringe was filled with 10 cm3 of sucrose solution. Step 4 The 10 cm3 of sucrose solution was transferred from the syringe to a dialysis tubing bag, as shown in Fig. 1.1. syringe sucrose solution open end of the dialysis tubing bag sucrose solution inside the dialysis tubing bag knotted end of the dialysis tubing bag Fig. 1.1 Step 5 A ruler was used to measure the distance from the knot to the meniscus of the sucrose solution in the bag, as shown in Fig. 1.2. finger dialysis tubing bag the distance from the knot to bottom of the meniscus the meniscus knot Fig. 1.2 Step 6 The dialysis tubing bag was placed into test-tube S and secured with an elastic band. Step 7 A measuring cylinder was used to pour 30 cm3 of distilled water into test-tube S, as shown in Fig. 1.3. elastic band open end of the dialysis tubing bag test-tube 30 cm3 of distilled water Fig. 1.3 Step 8 The student filled the second dialysis tubing bag with 10 cm3 of distilled water. Step 9 The student measured the distance from the top of the knot to the bottom of the meniscus of the distilled water in the dialysis tubing bag. Step 10 The dialysis tubing bag containing distilled water was then placed into test-tube DW and secured with an elastic band. 30 cm3 of distilled water was poured into test-tube DW. Step 11 Test-tubes S and DW were left for 15 minutes. Step 12 At 15 minutes the dialysis tubing bags were removed from test-tubes S and DW. (a) Fig. 1.4 shows the dialysis tubing bags at 0 minutes and at 15 minutes. 0 minutes 15 minutes 0 minutes 15 minutes dialysis tubing bag from test-tube S dialysis tubing bag from test-tube DW Fig. 1.4 (i) Measure the distance from the top of the knot to the bottom of the meniscus at 0 minutes and 15 minutes for the dialysis tubing bags from test-tubes S and DW. Prepare a table and record these measurements in your table. [3] (ii) Calculate the change in distance from the knot to the meniscus of the liquids in the dialysis tubing bags in test-tubes S and DW. S …… mm DW …… mm [1] (iii) Explain why it is important to take the measurements from the same place on the dialysis tubing bags shown in Fig. 1.4. …… [1] (iv) State a conclusion for the results of this investigation. …… [1] (v) Identify the variable that the student decided to change (independent variable) in this investigation. …… [1] (vi) Only one set of results was collected during this investigation. Explain why it is better to collect several sets of results. …… [1] (b) Another student repeated the investigation but their results were not the same. The student only used one syringe during the investigation and did not wash it. Suggest why the results of their investigation were not as expected. …… [1] (c) Sucrose can be broken down into reducing sugars. Describe how you would test for the presence of reducing sugars. …… [2] (d) Students investigated the effect of sucrose concentration on the mass of potato cylinders. • A potato was cut into cylinders. • The potato cylinders were all cut to 2 cm in length. • The initial mass of each potato cylinder was measured and recorded. • Each potato cylinder was put into a different concentration of sucrose solution. • The potato cylinders were left in the sucrose solutions for one hour. • The potato cylinders were removed from the sucrose solutions and the final mass of each potato cylinder was measured and recorded. (i) State two variables that were kept constant in this investigation. 1 …… 2 …… [2] The results of the investigation are shown in Table 1.1. Table 1.1 concentration initial mass of final mass of percentage change in of sucrose potato cylinder potato cylinder change in mass / g / mol per dm3 /g /g mass 0.00 2.13 2.29 0.16 7.5 0.20 2.05 2.08 0.03 1.5 0.40 2.52 2.42 –0.10 –4.0 0.60 1.68 1.52 –0.16 –9.5 0.80 1.56 1.32 –0.24 –15.4 1.00 2.51 2.08 –0.43 (ii) Calculate the percentage change in mass of the potato cylinder that was immersed in 1.00 mol per dm3 sucrose solution. Give your answer to one decimal place. Space for working. ……% [3] (iii) Plot a line graph on the grid of the concentration of sucrose solution against the percentage change in mass. One axis has been started for you. Include a curved line of best fit on your graph. 0.0 [4] (iv) Estimate the concentration of sucrose solution at which there was no percentage change in the mass of the potato cylinder. …… mol per dm3 [1] (v) Explain why the percentage change in mass is more useful than the change in mass when analysing the results in Table 1.1. …… [1] (e) State the name of the solution that is used to test for the presence of starch and give the result of a positive test. test solution …… positive result …… [2] [Total: 24]

Question

Fig. 2.1 is a photograph of a tomato fruit that has been cut in half. Fig. 2.1 (a) (i) Draw a large diagram of the tomato fruit shown in Fig. 2.1. [4] (ii) Describe how you could show that a tomato fruit contains vitamin C. …… [3] (b) Fig. 2.2 is a photomicrograph of a tomato seed. Q P magnification ×50 Fig. 2.2 Measure the length of line PQ on Fig. 2.2. length of PQ …… mm Calculate the actual size of the tomato seed using the formula and your measurement. length of line PQ magnification = actual length of the tomato seed Include the unit. Space for working. [3] (c) Plan an investigation to determine the optimum (best) temperature for germination of tomato seeds. …… [6] [Total: 16]