Students heard that waste water from a factory was polluting the local river. They decided to do some fieldwork to see if this was true. However, before they started their investigation their teacher warned them about the possible dangers of doing fieldwork in a polluted river. She also suggested some precautions they might take to protect themselves. (b) The students agreed on two hypotheses to investigate. Hypothesis 1: The river is most polluted near to the factory and the level of pollution decreases downstream. Hypothesis 2: Animal life in the river is affected by water pollution. To measure the level of water pollution the students did some research in the local library. They found some secondary data which showed the results of a study into the levels of dissolved oxygen and ammonia in the river. The results of the study included the following: • Oxygen is essential for animals to live in rivers. Polluted rivers have low dissolved oxygen levels. • Ammonia is a chemical which pollutes water. A summary of the secondary data is shown in Fig. 11 (Insert). (c) To investigate Hypothesis 2: Animal life in the river is affected by water pollution the students carried out the investigation described in Fig. 12 (Insert). They did the investigation at five sites along the river; these are shown in Fig. 11. (d) Table 3, below, shows the results of the students' fieldwork. The results are recorded using a tally method. Table 3 Fieldwork results Unpolluted Quality of water Very polluted Animal species Stonefly Mayfly Caddis fly Shrimp Water louse Leech Rat-tailed maggot Bloodworm Biotic score 10 8 7 6 5 3 3 2 Average Biotic Index score at the site Site 1 || || || | 55/7 = 7.9 Site 2 || | || 13/5 = 2.6 Site 3 | || || | 19/6 = 3.2 Site 4 | || | | | Site 5 || || | || 46/7 = 6.6 [Figure 11, Figure 12, Figure 13, Table 3]

1. (a)(i)Suggest two dangers which their teacher may have warned them about and suggest how they might protect themselves whilst working in a polluted river. Danger 1 Protection Danger 2 Protection[4]
2. (a)(ii)Give two ways that the students would be able to check if the river was polluted before they began their fieldwork. 1 2[2]
3. (b)(i)Having studied the secondary data shown in Fig. 11 the students agreed with Hypothesis 1: The river is most polluted near to the factory and the level of pollution decreases downstream. What evidence on Fig. 11 supports their conclusion?[2]
4. (b)(ii)Suggest why the level of pollution changes downstream from the factory.[2]
5. (c)(i)Why did the students disturb the river bed when carrying out the investigation?[1]
6. (c)(ii)Should the students have put the net upstream or downstream of the kick-sampling site? Explain your decision.[2]
7. (c)(iii)Why did the students need to identify the animals found while sampling at each site?[1]
8. (c)(iv)Why did the students do three tests at each site?[1]
9. (d)(i)Calculate the average Biotic Index score for site 4. Put your answer into Table 3. Show your calculation in the space below.[2]
10. (d)(ii)Plot the average Biotic Index score for sites 4 and 5 on Fig. 13 below. Site 4 is 10.5 km downstream and site 5 is 14 km downstream. [Figure 13 showing How Biotic Index changes downstream, with Biotic index 0-9 and distance downstream (km) 0-16. Existing plots for Site 1, Site 2, Site 3][2]
11. (d)(iii)How does the average Biotic Index score change downstream? Support your answer with evidence from Fig. 13.[3]
12. (d)(iv)The students reached a conclusion that Hypothesis 2: Animal life in the river is affected by water pollution is true. Give two pieces of evidence from Table 3 to support this conclusion. 1 2[2]
13. (e)Describe two other ways in which a river may be polluted, other than by waste water from a factory. 1 2[2]
14. (f)Suggest one hypothesis that students might investigate through fieldwork in a river which is not polluted. Describe how they would test their hypothesis. Hypothesis: How they would test it:[4]

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