Cambridge IGCSE Biology (9-1) 0970 — 2024 May/June Paper 5 · Variant 1

1 Cooking fruit and vegetables in water reduces their vitamin C content. The vitamin C is transferred from the fruit and vegetables to the water by diffusion. DCPIP can be used to estimate the concentration of vitamin C. The blue DCPIP solution reacts with the vitamin C solution and becomes colourless. You are going to investigate the effect of cooking time on the vitamin C content of the water. Read all the instructions but DO NOT DO THEM until you have drawn a table for your results in the space provided in 1(a)(i). You should use the safety equipment provided while you are doing the practical work. Step 1 Label the test‑tubes 1, 2, and 3. Place the test‑tubes in the test‑tube rack. Step 2 Wrap the piece of foil around the beaker containing the piece of citrus fruit, ensuring that the sides of the beaker are covered. Do not cover the top of the beaker. Step 3 Raise your hand when you are ready for hot water to be added to your beaker. The water should cover the piece of citrus fruit. If it does not, use the forceps to adjust the position of the piece of citrus fruit. Step 4 Start the stop‑clock and wait for one minute. Step 5 After one minute, use the 1 cm3 syringe to remove a 1 cm3 sample of the liquid from the beaker. Put this sample into test‑tube 1. Step 6 Wait for one more minute. Step 7 Use the 1 cm3 syringe to remove another 1 cm3 sample of the liquid from the beaker. Put this sample into test‑tube 2. Step 8 Repeat steps 6 and 7 with test‑tube 3. Step 9 Fill the 5 cm3 syringe with 5 cm3 of the DCPIP solution. Ensure that there are no air bubbles in the syringe. Step 10 Add one drop of the blue DCPIP solution to the liquid in test‑tube 1. Shake the test‑tube gently to mix the contents. Wait five seconds. Step 11 After five seconds, hold the white card behind the test‑tube to help you identify if the blue colour remains in test‑tube 1. If the contents of the test‑tube are blue continue to step 13. Step 12 If the contents of test‑tube 1 are not blue after five seconds repeat step 10. Continue adding drops of DCPIP solution until either the blue colour remains or the syringe is empty. Step 13 Record the volume of DCPIP solution remaining in the syringe in your table in 1(a)(i). Step 14 Repeat steps 9 to 13 with test‑tubes 2 and 3. Step 15 Calculate the total volume of DCPIP solution that you have added to each test‑tube using this equation: volume of DCPIP added = 5 – volume remaining in the syringe in step 13 Record these volumes in your table in 1(a)(i). (a) (i) Prepare a table and record your results. [5] (ii) State a conclusion for your results. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (b) (i) State the independent variable in this investigation. ..................................................................................................................................... [1] (ii) State the purpose of wrapping the beaker in foil in step 2. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Explain why it was important to remove the air bubbles from the syringe in step 9. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 9]

Mark scheme: 1(a)(i) 1 table drawn with minimum two columns and a header line ; 2 appropriate column / row headings, with units for (time and) volume ; 3 recording of three times/test-tubes and three volumes of DCPIP ; 4 correct trend ; 5 correct calculations of volume added ; 1(a)(ii) a correct conclusion for the candidate’s results ; 1 e.g. for the expect results: a longer (cooking) time allows more vitamin C to, diffuse out / AW, of the fruit 1(b)(i) time (fruit left in water) ; 1 1(b)(ii) decrease heat loss / insulation / maintain temperature / AW ; 1 1(b)(iii) idea of to make sure volume (of DCPIP) is accurate / air would affect the volume (of DCPIP) / incorrect volume (of DCPIP) would be recorded ; 1

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2 Plan an investigation to determine the effect of light intensity on photosynthesis in an aquatic plant. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [6]

Mark scheme: 2 independent variable 1 (at least) idea of two / different, light intensities ; dependent variable 2 (measuring) volume of, gas / oxygen, produced OR counting (number of) bubbles ; 3 and 4 detail of method ;; max two from:  method of changing light intensity e.g. different lamp distances / dimmer switch altered / different bulbs  method of, collecting gas / measuring volume of gas e.g. use of a gas syringe / ref to any quantitative displacement method  method to avoid heating effect of light e.g. heat shield / use LED bulbs to prevent heating  keep plant submerged / water added to cover the plant / weighing the plant down  idea of time for acclimatisation at each new light intensity / equilibration 5 and 6 constant variables ;; max two from:  time or volume (depending on method used) e.g., time to collect a set volume of oxygen / time to count number of bubbles OR volume / number of bubbles, in a set time  concentration of hydrogencarbonate added or same source of carbon dioxide  colour / wavelength, of light  temperature  same, type / species / (named) plant / age 7 two or more repeats ; 8 relevant safety ;

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3 (a) Fig. 3.1 is a photograph of a cross‑section of a persimmon fruit. P Q magnification ×2.2 Fig. 3.1 (i) Draw a large diagram of the persimmon fruit shown in Fig. 3.1. [4] (ii) Line PQ on Fig. 3.1 represents the diameter of the persimmon fruit. Measure the length of line PQ on Fig. 3.1. length of PQ ............................................... mm Calculate the actual diameter of the persimmon fruit using the formula and your measurement. length of line PQ in Fig. 3.1 magnification = actual diameter of the persimmon fruit Give your answer to three significant figures. Space for working. ......................................................... mm [3] (b) Plants can make fats, starch and proteins. (i) State the names of the reagents that can be used to test samples of plant tissue for starch and protein. starch ................................................................................................................................. protein ................................................................................................................................ [2] (ii) Describe the method you would use to test a sample of plant tissue for fat. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2]

Mark scheme: 3(a)(i) outline that is a single clear outer line ; size is at least the width of the image ; detail 1: six seeds shown and two openings without seeds ; detail 2: indents in external shape at the top and on both sides ; 4 3(a)(ii) line PQ = 104 1 mm ; 47.3 (mm) ;; 3 MP1 correct measurement of line PQ MP2 correct calculation to any number of significant figures MP3 correct rounding to three significant figures ecf from previous mark point if supported by workings 46.8 (for PQ of 103 mm) 47.7 (for PQ of 105 mm) 3(b)(i) starch: iodine solution ; protein: biuret solution ; 2 3(b)(ii) add ethanol and (then) water ; shake ; 2 3(c)(i) volume of, juice / (filtered) liquid / filtrate ; 1 3(c)(ii) any one from:  volume of pectinase / 50 cm3 of pectinase  incubation time / time in water(-bath) / 30 minutes in water(-bath)  temperature / 37 ⁰C  type of, fruit / juice ; 1 3(c)(iii) hazard: enzyme / pectinase ; precaution: goggles / gloves ; OR hazard: cutting / chopping (apple) ; precaution: cut away from body / cut onto a hard surface ; 2 Question Answer Marks Guidance 3(c)(iv) to identify anomalous results ; 1 3(c)(v) the same volume of, water / boiled pectinase / denatured pectinase ; 1 3(d)(i) 138 ; cm3 ; 2 MP1 correct calculation (150  0.92 = )138 MP2 correct unit 3(d)(ii) axes labelled with units ; suitable linear scale and data occupies at least half the grid in both directions ; six points plotted accurately  half a small square ; suitable line drawn ; 4 3(d)(iii) as concentration increases, volume increases ; levels off / AW, at 0.8 (%) OR no further increase after 0.8(%) ; 2

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