34 11 White clover plants provide a rich source of nitrogen for cattle when grown with grass plants in fields. The photograph shows a clover plant growing in a field of grass. A student noticed that the grass plants growing near patches of clover were a darker green than other grass plants. (a) Devise an investigation to show whether the presence of clover plants affects the concentration of the green pigment chlorophyll in grass plants. 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(b) Clover plants have bacteria living in root nodules. These bacteria convert atmospheric nitrogen (N2) to ammonia (NH3) using the enzyme nitrogenase. (i) State one organic molecule containing nitrogen atoms which is found in plant cells. (1) .................................................................................................................................................................................................................................................................................... (ii) Nitrogen is a relatively unreactive gas that forms 80% of the atmosphere. The enzyme nitrogenase catalyses the reaction shown: N2 + 8H+ + 16 ATP → 2NH3 + H2 + 16 ADP + 16 Pi The activation energy for this reaction is very high. Analyse the information to explain how the enzyme nitrogenase is involved in the energy changes required for this reaction. 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(Total for Question 11 = 11 marks) TOTAL FOR PAPER = 120 MARKS 36 BLANK PAGE