page 12 23. The graph shows species richness of mollusc populations in areas of fenland. The number of species of mollusc was recorded in several areas as well as the calcium concentration in the fenland water. At each site the concentration of iron was also measured. 0 10 20 30 40 0 100 200 calcium (mg/l) low iron concentration Key high iron concentration number of species 300 400 Which of the following generalisations can be drawn from the graph? A An increase in calcium from 100 to 400 mg/l increases the species richness B High iron concentration leads to the highest species richness C When both calcium and iron concentrations are high the species richness is highest D An increase in calcium up to 150 mg/l increases species richness 24. New patterns of resistance in Plasmodium have increased the challenge experienced in the treatment of malaria. Which of the following strategies is least likely to reduce the challenges in the treatment and control of malaria? A Improved sanitation B Development of new culture methods for Plasmodium C Coordinated vector control D Building of new low-density housing in malarial areas