6 Mining may result in the release of heavy metal ions, causing pollution of lakes and rivers. High concentrations of these heavy metal ions, such as cadmium (Cd2+) and copper (Cu2+), decrease the rate of photosynthesis in plants. (a) Cadmium ions disrupt the function of photosystem II in chloroplasts. (a)(i) Name the part of the chloroplast where photosystem II is located. (a)(ii) Describe the role of photosystem II in the absorption of light. (b) An investigation was carried out into the effect of cadmium ion concentration on the aquatic, single-celled, photosynthetic protoctist, Chlamydomonas reinhardtii. The activity of photosystem II was measured at different concentrations of cadmium ions. • Four different concentrations of cadmium ions were used, 0, 1, 10 and 100 μmoldm−3. • C. reinhardtii was allowed to acclimatise in the dark before the experiment started. • At time 0 min the light was switched on and the cadmium ions were added. • At each concentration, the activity of photosystem II was measured over a period of 60 minutes. • Each experiment was carried out under the same controlled conditions. The results are shown in Fig. 6.1. [Figure 6.1] Describe the effects of cadmium ion concentration on the activity of photosystem II, as shown in Fig. 6.1. (c) Copper(II) ions (Cu2+) inhibit the function of a proportion of the chlorophyll a present in single-celled, photosynthetic protoctists. The concentration of functional chlorophyll a in these organisms was measured in two different months of the same year in an unpolluted lake and in a lake polluted with copper ions. The results are shown in Table 6.1. [Table 6.1] (c)(i) Describe and suggest explanations for the results shown in Table 6.1. (c)(ii) Copper ions can replace other metal ions present in organic molecules. Suggest how copper ions change the structure of chlorophyll a. (d) Chromatography is a method that can be used to separate and identify different photosynthetic pigments in a chloroplast extract. Describe how chromatography is used to identify chlorophyll a in an extract from chloroplasts.