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]