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Biology · May / June 2020 · Paper 61 · Question 1

0610

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The question as text

Sugars are a source of energy in the diet. A student wanted to estimate the concentration of glucose in an energy drink (D). Step 1 Three test-tubes were labelled A, B and C. Step 2 Three different concentrations of glucose solution were prepared as shown in Table 1.1.

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  • 1(a)(i)[1]

    5.0 ;

  • 1(a)(ii)[1]

    (initial temperature) 80 and (final temperature) 60 ;

  • 1(a)(iii)[3]

    table drawn with two columns and a header row ;

    column headings with unit: test-tube and time (taken for colour change) / s ;

    four correct times recorded in seconds (A:36, B:87, C:165, D:90) ;

  • 1(a)(iv)[1]

    2(%);

  • 1(a)(v)[1]

    idea of comparing the time for D with A, B and C / B was the closest time to D / AW ;

  • 1(b)(i)[2]

    error: temperature has decreased ;

    improvement: maintain temperature by, using a thermostatically controlled water-bath / Bunsen burner / adding hot water throughout the investigation (and monitoring) temperature / insulate beaker / AW ;

  • 1(b)(ii)[1]

    times are slower as temperature decreases / unable to identify the concentration of glucose in D with certainty / may underestimate the concentration ;

  • 1(c)(i)[2]

    any two from:

    volume of glucose solution ;

    volume of Benedict’s solution ;

    concentration of Benedict’s solution ;

    time for mixing of test-tube contents ;

  • 1(c)(ii)[1]

    heating liquid (that might spill out of test-tube) / use of Benedict’s solution / AW ;

  • 1(d)(i)[4]

    axes correctly labelled with units: time / minutes and mass of starch remaining / g ;

    scale evenly spaced and occupying half of the grid in both directions ;

    five correct plots ± half a small square ;

    line joining all five plot points ;

  • 1(d)(ii)[1]

    mass of starch remaining decreases and levels off / AW ;

  • 1(d)(iii)[2]

    mass correct from candidate’s graph ;

    graph marked at interpolation to show where reading taken ;

  • 1(d)(iv)[1]

    (42 ÷ 5 =) 8.4 (g per minute) ;

  • 1(e)[6]

    method:

    1&2 use of Benedict’s reagent to measure reducing sugar produced, at set time / at regular intervals ;

    ref. to use of hot water-bath / use of (thermostatically controlled) water-bath to maintain temperatures ; OR

    use of iodine solution to determine starch remaining ;

    ref. to drops on spotting tile at regular intervals ;

    independent variable:

    3

    ref. to using at least two different temperatures ;

    variables kept constant – max two from mp 4-8:

    4

    same type of enzyme ;

    5

    concentration of starch suspension ;

    6

    concentration of enzyme ;

    7

    same pH ;

    8

    incubating enzymes and starch suspension for same time ;

    dependent variable:

    9

    concentration of reducing sugar produced / time taken for drops and iodine solution to remain brown ;

    10

    ref. to at least two further replications / repeat investigation two more times ;

    11

    ref. to relevant safety precaution ;

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