Cambridge IGCSE Biology (9-1) 0970 — 2021 Oct/Nov Paper 6 · Variant 2

1 A student investigated the effect of temperature on the rate of respiration in yeast cells. When yeast cells respire they produce carbon dioxide gas. In this investigation the gas was collected in a balloon that was attached to a test-tube containing a yeast suspension. Step 1 The student prepared a hot water-bath and a cold water-bath. Step 2 The student measured the temperature of the water in the hot water-bath and in the cold water-bath. Step 3 A yeast suspension was stirred with a glass rod. 25 cm3 of the yeast suspension was put into each of two test-tubes. Step 4 A balloon was stretched over the top of each test-tube. Step 5 One test-tube and balloon was put into the hot water-bath and the other test-tube and balloon was put into the cold water-bath, as shown in Fig. 1.1. balloon test-tube yeast suspension water-bath Fig. 1.1 Step 6 The circumference of each balloon was measured by placing a piece of string around the widest part of the balloon, as shown in Fig. 1.2. A ruler was then used to measure the length of the string that wrapped around each balloon once. balloon string wrapped around the balloon at the widest part top of the test-tube Fig. 1.2 Step 7 The circumference of each balloon was measured at 0 minutes, 5 minutes, 10 minutes and 15 minutes. The student’s results are shown in Fig. 1.3. Cold 0 minutes – 120 mm Hot 0 minutes – 120 mm 5 minutes – 125 mm 5 minutes – 135 mm 10 minutes – 132 mm 10 minutes – 145 mm 15 minutes – 137 mm 15 minutes – 147 mm Fig. 1.3 (a) (i) Prepare a table and record the results shown in Fig. 1.3. [3] (ii) State a conclusion for the results shown in Fig. 1.3. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Suggest why it was important to stir the yeast suspension in step 3. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (iv) State two variables, other than stirring, that should be kept constant in this investigation. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2] (b) (i) Balloons and string were used to collect and measure the gas produced by the yeast cells. Suggest another, more accurate, method of collecting and measuring the gas. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (ii) State the name of an indicator which could be used to show that the gas produced by the yeast is carbon dioxide and give the result of a positive test. indicator ............................................................................................................................. positive test result ............................................................................................................. [2] (c) (i) The temperatures of the water in the hot water-bath and in the cold water-bath were measured again at the end of the investigation. Fig. 1.4 is a diagram of the thermometers showing the temperatures in the two water-baths. hot water-bath cold water-bath °C °C 40 40 30 30 20 20 Fig. 1.4 Complete Table 1.1 by recording the temperatures from Fig. 1.4 and calculating the change in temperature. Table 1.1 temperature at temperature in change in water-bath the end of the step 2 / °C temperature / °C investigation / °C hot 40 cold 20 [2] (ii) Describe how the method could be modified to prevent a change in the temperature of a water-bath. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 13]

Mark scheme: 1(a)(i) 1 table drawn with a line between headings and data and (at least) 3 columns ; 2 column / row headings with units: time / minutes circumference or length / mm hot and cold ; 3 eight circumferences recorded correctly and times recorded correctly ; 1(a)(ii) yeast cells respire more (rapidly) at a higher temperature / AW / ora OR higher volume of gas / carbon dioxide, produced at higher temperature / ora ; 1 1(a)(iii) idea of uniform, distribution / concentration (of yeast cells) / AW ; 1 1(a)(iv) any two from: type / age, of yeast ; concentration of yeast suspension ; volume of yeast suspension ; type of balloon ; time ; (maintained) temperature(s) of water-bath(s) ; AVP ;; 2 1(b)(i) (gas) syringe OR (bung)+(delivery tube) +inverted measuring cylinder over water / AW OR downward displacement of water in a graduated container / AW ; 1 Question Answer Marks Guidance 1(b)(ii) limewater ; milky / white / cloudy / AW ; OR hydrogencarbonate ; yellow ; 2 1(c)(i) two temperatures recorded as: hot 28(°C) AND cold 20(°C) ; two changes in temperature calculated as hot 12(°C) cold 0(°C) ; 2 ecf MP2 from incorrect MP1 redings 1(c)(ii) any one from: 1 use thermostatically controlled water-baths ; 2 use a Bunsen burner AND thermometer (method outlined) / use a Bunsen burner and monitor the temperature ; 3 top up with, hot water / cold water / ice, and monitor /use a thermometer ; 4 insulate the container / AW ; 1

More questions on Aerobic respiration

2 Fig. 2.1 is a photograph of a flower from the wind-pollinated grass plant, Briza maxima. Fig. 2.1 (a) (i) Draw a large diagram of the flower in Fig. 2.1. [4] (ii) Fig. 2.2 is a photomicrograph of grass pollen grains. P Q magnification ×1500 Fig. 2.2 Measure the length of line PQ on Fig. 2.2. length of PQ ............................................... mm Calculate the actual length of the pollen grain using the formula and your measurement. length of line PQ magnification = actual length of the pollen grain Give your answer in millimetres and to two decimal places. Space for working. ......................................................... mm [3] (b) Scientists investigated the effect of wind speed on the average distance travelled by single pollen grains and groups of five pollen grains joined to form a clump. The pollen grains were dropped from a height of 2 m. The results of the investigation are shown in Table 2.1. Table 2.1 average distance average distance wind speed travelled by single travelled by clumps / m per s pollen grains of five pollen grains / m / m 0.0 0 0 0.2 38 21 0.4 81 39 0.6 118 55 0.8 154 70 (i) Calculate the percentage decrease in the average distance travelled when the pollen grains fell as a clump compared to a single pollen grain, at a wind speed of 0.6 m per s. Give your answer to two significant figures. Space for working. ............................................................ % [3]

Mark scheme: 2(a)(i) 1 single clear lines for outline ; 2 uses at least half available space (70+ mm length without stalk) ; 3 detail 1 at least 6 sections, indicated with lines, on either side ; 4 detail 2 at least 3 overlapping sections or indication of ‘zig zag line’ down the centre ; 4 2(a)(ii) 62 (mm) ± 1 mm ; 0.04 (mm) ;; 3 MP1 correct measurement of line PQ MP2 correct substitution (62 ÷ 1500) or 0.04133r MP3 correct rounding to two decimal places ecf MP2 and MP3 if previous MP incorrect 2(b)(i) (–)53(%) ;;; 3 MP1 correct data selection (118 and 55) MP2 correct calculation MP3 correct rounding to two significant figures ecf MP2 and MP3 if previous MP incorrect 2(b)(ii) 1 axes labelled with units : wind speed / m per s AND (average) distance / m ; 2 even scale with plots occupying at least half the grid in both directions ; 3 0.0, 0.6 and 0.8 points plotted accurately for both sets of data, ± half a small square ; 4 line drawn for each data set plotted ; 5 correct key given ; 5 2(b)(iii) intersection with line shown on graph ; correct reading of value from graph for 0.5 ms–1 ; 2 2(b)(iv) add Benedict’s (solution / reagent) ; heat ; red / orange / yellow / green, (colour) ; 3 Question Answer Marks Guidance 2(c)(i) any six from: independent variable: 1 at least two different temperatures ; dependent variable: 2 measure mass of leaves before and after / measuring the movement of bubble / meniscus, in capillary tube of potometer / measuring mass of pot and soil before and after / observing change in colour of (anhydrous) cobalt chloride paper ; method: 3 method of maintaining at least one of the temperatures ; 4 description of, suspending leaves (on a line) / use of potometer / wrapping whole pot and soil in a bag ; 5 further description of how the apparatus would be set up ; 6 wait for set period of time ; 7,8 constant variables max two from: ;; • wind speed • humidity • light intensity • carbon dioxide concentration • size / mass / weight / surface area / number of leaves / shoot/plant • plant or leaves: same species / age / condition 9 repeat the whole investigation at least two times (three trials) ; 10 safety ; 11 AVP ; 6 Question Answer Marks Guidance 2(c)(ii) any one from: to decrease humidity: dehumidifier / use a desiccant / AW ; to increase humidity: bowls of hot water around apparatus / place in plastic bag / AW ; 1

More questions on Sexual reproduction in plants