The pollution of air and water may result from human activity. This pollution can lead to many harmful effects on ecosystems. A knowledge of these harmful effects has led to a reduction in human activity that leads to this pollution. (a) One human activity that may lead to pollution of air is the production of electricity. The graph shows changes in the release of gases into the air during the production of electricity over a period of 18 years by 32 countries. [Figure 2 (Line graph showing percentage concentration of gas compared with the concentration in 1990 on the y-axis, from 0 to 100, against year on the x-axis, from 1990 to 2008. Three lines are plotted: carbon dioxide (decreasing from ~100 to ~80), oxides of nitrogen (decreasing from ~100 to ~40), and sulfur dioxide (decreasing from ~100 to ~20).)]

1. (a)(i)Describe, using data from the graph, the trends shown.[4]
2. (a)(ii)During this period of 18 years, the total amount of electricity produced each year by the 32 countries increased. Suggest one change in the processes used by these countries to produce electricity that may account for the trends shown in the graph.[1]
3. (a)(iii)Pollution of the air by each of the gases named in the graph leads to harmful effects on ecosystems. Suggest and explain the positive effects on ecosystems of the trends shown in the graph.[3]
4. (b)(i)A survey of the populations of several species of fish in part of a river was carried out in 2003 and again in 2007. The population of one species of fish decreased from 1385 to 28 over this period. Calculate the percentage decrease in the population of this species of fish.[1]
5. (b)(ii)The scientists who carried out the surveys suggested that the fish population might recover if conservation actions are taken. Suggest one possible conservation action that could be recommended by the scientists and describe how they could find out whether this action is successful.[3]

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