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O-LevelGeographyThe natural environment2217/23 · Oct/Nov 2014 · Q730 Marks

Two groups of students were doing fieldwork in the Rio Santa Valley in Peru. They chose four sites along the river to investigate how the river changes downstream. The students investigated the following hypotheses: Hypothesis 1: River velocity increases downstream. Hypothesis 2: Rocks on the bed of the river (bedload) become smaller and more rounded downstream.

  1. (a)Each group used two different methods to measure velocity. In method 1 they used floating objects and in method 2 they used a velocity meter (flow meter). The velocity meter and how it is used are shown in Photograph B and Fig. 10 (Insert). Describe the two different methods of measuring velocity. Method 1 (using floating objects) Method 2 (using a velocity meter)[6]
  2. (b)(i)The students agreed that method 1 (using floating objects) had produced unreliable results compared to method 2 (using a velocity meter). Suggest three reasons why method 1 may have produced unreliable results.[3]
  3. (b)(ii)The results of the students' measurements using a velocity meter are shown in Table 1 (Insert). Use the average velocity results to complete the graph for Group A in Fig. 11 below.[2]
  4. (b)(iii)What conclusion would the students in Group B make about Hypothesis 1: River velocity increases downstream? Support the conclusion with evidence from Fig. 11.[2]
  5. (c)(i)At each site the two groups of students selected 10 rocks at random from the river bed. They then measured the size and roundness of each rock using the equipment shown in Fig. 12 (Insert). Describe how the students made the two measurements. Size Roundness[2]
  6. (c)(ii)Suggest two weaknesses of selecting rocks at random.[2]
  7. (c)(iii)The results obtained by the two groups are shown in Table 2 (Insert). Plot the results of group B at site 3 on Fig. 13 below.[2]
  8. (c)(iv)When they looked at their results the students in Group A came to the conclusion that Hypothesis 2: Rocks on the bed of the river (bedload) become smaller and more rounded downstream, was false. Give two pieces of evidence from their results in Fig. 13 to show why the students in Group A made this conclusion.[2]
  9. (d)(i)Explain why rocks generally become smaller and more rounded downstream.[3]
  10. (d)(ii)The students then thought about how they could improve the reliability of the method used during fieldwork if they repeated the task for Hypothesis 2: Rocks on the bed of the river (bedload) become smaller and more rounded downstream. Give two ways the reliability of the method could be improved.[2]
  11. (e)Whilst the two groups of students worked on Hypotheses 1 and 2, other students were investigating different hypotheses. Describe a method to investigate the hypothesis: The river channel becomes wider and deeper downstream.[4]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2014). The mark or mark type is shown in brackets.

  1. [6] (a) Method 1: Measure length of river (10m)/divide into sections/ranging poles to mark out section/set up start and finishing points Put orange/dog biscuit/float/floating object into river Time float moving over distance Repeat and calculate average/repeat across river channel Calculate velocity by dividing distance by time Method 2: Put velocity meter/propeller/it below surface of river/in/into river/in/into the water Propeller must be facing upstream/nothing in front of propeller Read/look at digital/velocity reading/display/speed is shown on display Take several readings over time and calculate average/take readings across river channel and calculate average If answers are wrong way only round credit relevant point about repeat and calculate average Reserve 2 marks for each method
  2. [3] (b)(i) Floats got stuck in channel/hit objects/vegetation in channel Operator error/error in calculation Measurements not easy to take at different points across river/float doesn't move in straight line Floats affected by wind Only measures surface velocity
  3. [2] (b)(ii) Completion of Group A line graph at points 3 (1.1 m/s) and 4 (1.6m/s) Look at 2 plots and completed line -1 for each error (wrong plot(s)/incomplete line)
  4. [2] (b)(iii) Hypothesis is true/velocity does increase downstream – 1 mark reserve 1 mark for average velocity data from two sites from group B e.g. site 1 = 0.7 and site 4 = 1.7; site 2 = 0.8 and site 3 = 1.2 Overall/downstream/over the 4 sites from 0.7 to 1.7
  5. [2] (c)(i) Size: used a ruler to measure long axis/length of pebble Roundness: used information from the chart/compared pebble with the chart
  6. [2] (c)(ii) Rocks selected may not be typical of the rocks at that site/anomaly All rocks may have been taken from same area of river bed/not across channel/taken from same place Not a fair/reliable sample/students choose rock/bias
  7. [2] (c)(iii) Plot two bars on graph: average length of long axis = 15.4cm average roundness score = 3.9
  8. [2] (c)(iv) Average length of long axis at site 1 = 5.0 at site 3 =9.7 Average length of long axis at site 1 = 5.0 at site 4 = 9.3 Accept reference to any 2 sites and lengths Average roundness score almost the same/similar for all sites + data from any 2 sites OR Accept reference to any 2 sites and roundness scores which show decrease in roundness i.e. NOT sites 1 and 2 or sites 3 and 4 in combination Roundness score at site 1 = 4.5 at site 4 = 4.3 Roundness score at site 2 = 4.6 at site 3 = 3.6 1 mark for length and 1 mark for roundness Allow tolerance of 0.1 on all measurements from Group A No hypothesis mark
  9. [3] (d)(i) Eroded by water Attrition/pebbles crash into each other/river bed/bank Corrosion/solution/dissolves rocks Smaller/rounder pebbles are moved further downstream because they are easier/lighter to transport
  10. [2] (d)(ii) Repeat measurement(s) to check accuracy/other student measures to check accuracy Sample/measure more pebbles at each site/take more measurements at each site Use callipers/pebbleometer/measure weight or volume of pebbles Systematic sampling technique/sample rocks from inside, middle and outside Test at more sites
  11. [4] (e) Select/find more fieldwork sites downstream/along the river Stretch measuring tape/rope across channel/from one bank to the other Record measurement of width (in metres) Rest rule/ruler/ranging pole on river bed/lower rock on string to river bed Make sure ruler is upright/vertical/make sure string is taut Measure depth at regular intervals across channel (every metre) Read off the scale where water level reaches/where ruler is wet Record measurement of depth (in cm/metres) Only credit 1 mark for recording measurement

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About this question

Topic
The natural environment, O-Level Geography (syllabus 2217). Structured question, 30 marks.
Source
O-Level Geography, Oct/Nov 2014 Paper 2 Variant 3, question 7.

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