The graph shows the variation in the concentration of dissolved carbon dioxide in the water of a pond over a period of 24 hours. [Graph showing concentration of dissolved carbon dioxide over 24 hours (night, day, night)]

1. (a)(i)Explain how plants that live in the water contribute to the changes in concentration of dissolved carbon dioxide shown in the graph.[4]
2. (a)(ii)Draw a line on the graph above to show how the concentration of dissolved oxygen in the water of the same pond is likely to change over the same period of time.[2]
3. (b)Carbon dioxide dissolves in water to form an acidic solution. The higher the concentration of dissolved carbon dioxide, the lower the pH. Ammonia is a toxic chemical found in ponds, that may harm fish. The graph shows how the concentration of dissolved ammonia in the water of a pond changes as the pH changes. [Graph showing % ammonia vs pH] Use this graph and the graph on page 8 to suggest and explain at which time of day fish that live in the pond are most likely to be affected by the toxic effects of ammonia. Draw a ring around the correct time of day. time of day sunrise midday sunset explanation[4]

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