Students in southern USA read a newspaper report about pollution in a local river. They decided to do some fieldwork to investigate this. However, before they started their fieldwork, their teacher warned them about the possible dangers of working in polluted water. She also suggested some precautions they might take to protect themselves.

1. (a)(i)Suggest two dangers which their teacher may have warned them about when working in polluted water, and suggest how they might protect themselves whilst testing the level of pollution in the river. Danger 1 Protection Danger 2 Protection[4]
2. (a)(ii)First the students did a visual survey of the river. Suggest two ways that they would be able to see from the river bank if the river was polluted. 1 2[2]
3. (b)The students agreed on two hypotheses to investigate. Hypothesis 1: Water pollution increases as you go downstream. Hypothesis 2: The Biotic Index decreases as you go downstream. The Biotic Index is a way of measuring water pollution by looking at the animals that live in the river. To measure the level of water pollution the students decided to measure pH and oxygen levels in the river and do a simple foam test. • pH is a measure of the acidity of water. The pH score decreases as water becomes more acidic. More acidic water means that pollution is more likely. • The oxygen level of water decreases as it becomes more polluted. The students used a digital meter to measure the pH of the water. This meter is shown in Photograph B (Insert).
4. (b)(i)Describe two ways in which the students could make sure that their measurements were reliable. 1 2[2]
5. (b)(ii)To measure the oxygen level and to do the foam test the students took samples of river water back to school. One student described the classroom tests in her fieldwork notebook. This is shown in Fig. 7 (Insert). Suggest two reasons why these two tests may not be as reliable as using a digital meter. 1 2[2]
6. (b)(iii)Use the results in Table 2 (Insert) to complete Fig. 9 below. [Figure 9 shows two incomplete bar charts. The top chart shows 'time taken for dye to disappear (days)' against 'distance downstream from source (km)'. Bars are missing for 5km and 25km. The bottom chart shows 'time taken for foam to disappear (minutes)' against 'distance downstream from source (km)'. Bars are missing for 5km and 25km.][2]
7. (b)(iv)Do the results shown in Figs 8 and 9 support Hypothesis 1: Water pollution increases as you go downstream? Use data to support your conclusion.[4]
8. (b)(v)Suggest two reasons why water pollution levels may vary along a river. 1 2[2]
9. (c)To investigate Hypothesis 2: The Biotic Index decreases as you go downstream, the students did the investigation described in Fig. 10 and shown in Photograph C (Insert) at the five sites along the river.
10. (c)(i)Before the students began working at the five fieldwork sites they did a pilot study at a place on the river near to their school. Give two advantages of doing a pilot study. 1 2[2]
11. (c)(ii)Explain why the students disturbed the river bed when carrying out the fieldwork.[1]
12. (c)(iii)Explain why the students needed to identify the different types of animals found at each site while sampling.[1]
13. (d)Fig. 11 below shows the students' recording sheet for site 3. They recorded their results using a tally method. [Figure 11 shows a recording sheet for site 3 with a table for 'Type of animal species' and 'Number found'. Scud and Dragonfly are listed with numbers 2 and 5 respectively. Another table shows Groups 1, 2, 3 of species with their biotic score and number found, some with tallies (e.g., Caddisfly with one dash, Sowbug with '///', etc.).]
14. (d)(i)Complete Fig. 11 below by recording the following information using the tally method. Type of animal species | Number found Scud | 2 Dragonfly | 5[1]
15. (d)(ii)Calculate the total Biotic score for Dragonfly at site 3 in Table 3 below. The total Biotic score is calculated by multiplying the Biotic score of a species by the number of this species found. Table 3 Biotic Index scores at Site 3 Species | Biotic score of species | Number of each species found | Total Biotic score Riffle beetle | 9 | 1 | 9 Sowbug | 8 | 3 | 24 Damselfly | 7 | 2 | 14 Crayfish | 7 | 3 | 21 Scud | 6 | 2 | 12 Dragonfly | 6 | 5 | Midgefly | 5 | 1 | 5 Blackfly | 5 | 1 | 5 Total | | 18 | 120[1]
16. (d)(iii)Table 4 below shows a summary of the students' results at the 5 sites. The average Biotic Index score is the total Biotic score divided by the number of animals. Table 4 Students' Biotic Index results Unpolluted | Quality of water | Very polluted Group 1 species | Group 2 species | Group 3 species | Average Biotic Index score at the site Site 1 | 10 | 6 | 0 | 136/16 = 8.5 Site 2 | 8 | 9 | 0 | 134/17 = 7.9 Site 3 | 1 | 15 | 2 | 120/18 = 6.7 Site 4 | 0 | 11 | 5 | 100/16 = 6.3 Site 5 | 0 | 9 | 7 | 91/16 = 5.7 Use the results in Table 4 to plot the average Biotic Index score for sites 3 and 5 on Fig. 12 below. Site 3 is 18 km downstream and site 5 is 25 km downstream. [Figure 12 is a line graph titled 'How the Biotic Index changes downstream', showing 'average Biotic Index' on the y-axis and 'distance from river source (km)' on the x-axis. Data points for sites 1, 2, and 4 are plotted. Site 3 and Site 5 points are missing.][2]
17. (d)(iv)The students came to the conclusion that Hypothesis 2: The Biotic Index decreases as you go downstream was correct. What evidence from Table 4 and Fig. 12 supports their conclusion?[2]
18. (d)(v)Look again at Fig. 10 and Table 4. How does the data about animal species in Table 4 also show that the water becomes more polluted downstream?[2]

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