Question 123 marks
Question
Some animals live in cold places. They sometimes huddle together as shown in Fig. 1.1. Fig. 1.1 You are going to investigate the effect of huddling on heat loss from model animals. Test-tubes filled with hot water will represent the animals. 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. Raise your hand when you are ready for hot water to be poured into the beaker that is wrapped in foil. Step 1 Half-fill one test-tube with hot water and place it in the empty beaker. Step 2 Put the thermometer into the test-tube containing hot water. Step 3 Measure the temperature of the hot water in the test-tube. Record this temperature in your table in 1(a)(i). Step 4 Leave the thermometer in the test-tube and start the stop-clock. Step 5 After one minute, measure the temperature of the hot water in the test-tube. Record the temperature in your table in 1(a)(i). Step 6 Measure and record the temperature of the hot water in the test-tube every minute for a total of five minutes. Step 7 Remove the thermometer from the test-tube and carefully empty the water from the test-tube into the beaker labelled waste. Step 8 Place three test-tubes together and keep them together with the elastic band, as shown in Fig. 1.2. elastic band Fig. 1.2 Step 9 Place the group of three test-tubes into the empty beaker. Half-fill all three test-tubes with hot water. Step 10 Place the thermometer into any one of the three test-tubes. Step 11 Repeat step 3 to step 7 with this group of three test-tubes. Step 12 Remove the elastic band from the group of three test-tubes. Make a group of seven test-tubes and keep them together with the elastic band, as shown in Fig. 1.3. put the thermometer into the central test-tube elastic band Fig. 1.3 Step 13 Place the group of seven test-tubes into the empty beaker. Half-fill all seven test-tubes with hot water. Step 14 Place the thermometer into the central test-tube. Step 15 Repeat step 3 to step 7 with this group of seven test-tubes. (a) (i) Prepare a table to record the results of this investigation. [4] (ii) Plot a line graph on the grid of temperature against time. Include all three sets of data from your table in 1(a)(i) and a key. [5] (iii) State two conclusions for this investigation. 1 …… 2 …… [2] (iv) State two variables that were kept constant during this investigation. 1 …… 2 …… [2] (v) Suggest two possible sources of error in this investigation. 1 …… 2 …… [2] (vi) Suggest one improvement to the method that you used in this investigation. …… [1] (vii) Identify one hazard for this investigation. …… [1] (b) In mammals, respiration releases heat energy to maintain an optimum temperature for enzyme activity in the body. Amylase is an enzyme that catalyses the breakdown of starch into reducing sugars. Plan an investigation to identify the temperature at which the enzyme amylase is most active. …… [6] [Total: 23]
Mark scheme
1(a)(i) table drawn with at least four, columns / rows and a header 4 line ; two suitable headings with units ; MP2 temperature / °C and time / minutes OR temperature / °C and number of (test-)tubes all three sets of data recorded (15 values) ; starting temperature is higher than the final temperature in the single test-tube 1 ; 1(a)(ii) axes labelled with units ; 5 suitable linear scale and data occupies at least half the grid in both directions ; data points plotted to an accuracy of ± half a small square ; suitable line drawn for each of the three data sets ; key correctly identifies each of the three data sets ; 1(a)(iii) huddling, reduces heat loss / conserves more heat ; ora 2 the more test-tubes the slower, the temperature drops / heat loss ora OR as time increases, temperature falls / heat is lost ; AVP ;; i.e. suitable conclusions for the candidate’s data 1(a)(iv) any two from: 2 (same) size test-tubes ; (same) type / kind , of test-tubes ; all test-tubes placed in a beaker ; (same) total experimental time / described ; (same) time intervals (between sampling) ; AVP ;; e.g. kept in an insulated beaker 1(a)(v) any two from: 2 volume of water, not the same / could vary / AW ; temperature (of water) not measured at , start / 0 minutes ; start temperature, not the same / could vary / AW ; no band around 1 test-tube/ bands only on 3 & 7 test-tubes OR no insulating effect in 1 test-tube / band on 3 & 7 test- tubes absorbs heat ; band tightness, not the same / could vary / AW ; room / environmental / surrounding, temperature, not the same / could vary / AW ; AVP ;; other suitable errors for this experiment 1(a)(vi) any one from: 1 repeat the whole investigation (at least) twice more / AW ; same volume of water ; temperature (of water) measured at , start / 0 minutes ; same starting temperature ; band around 1 test-tube ; band tightness the same ; maintain the, room / environmental , temperature ; AVP;; other suitable improvements based on the experiment 1(a)(vii) (use of) hot, water / test-tubes / equipment 1 OR (use / breakage, of) glass (equipment) ; 1(b) either – reducing sugar method 6 independent variable 1 at least three temperature values, tested / stated ; dependent variable 2 time to (first) (correct) colour change (of Benedict’s) / (correct) colour (of Benedict’s) after a set period of time / mass of precipitate in a fixed time ; 3, 4 and 5 variables kept constant ;;; concentration of , amylase / enzyme (solution) volume / mass, of, amylase / enzyme (solution) pH volume of starch (solution) / mass of starch / mass of plant material / size of plant material concentration of starch (solution) 6, 7 and 8 method ;;; equilibration (both solutions in water bath before mixing) take (fixed volume of) samples (testing with) Benedict’s (solution) use of buffer use of, colorimeter / colour chart use of, balance / AW, to measure mass of precipitate method of maintaining temperature 9 repeat investigation twice / at least two replicates ; 10 relevant safety precaution – e.g. gloves / goggles / tongs / test-tube holder ; 1(b) OR disappearance of starch method independent variable 1 at least three temperature values, tested / stated ; dependent variable 2 time for iodine solution to stay yellow-brown / time for disappearance of starch / colour of iodine (solution) after a set period of time ; 3, 4 and 5 variables kept constant ;;; concentration of, amylase / enzyme (solution) volume / mass, of, amylase / enzyme (solution) pH volume of starch (solution) / mass of starch / mass of plant material / size of plant material concentration of starch (solution) 6, 7 and 8 method ;;; equilibration (both solutions in the water bath before mixing) take samples (testing with) iodine (solution) use of, spotting / white, tile use of buffer use of, colorimeter / colour chart method of maintaining temperature 9 repeat investigation twice / at least two replicates ; 10 relevant safety precaution – gloves / goggles ;