20 7 A range of minerals is necessary for the formation of healthy plant tissue. (a) Which molecule contains magnesium ions? (1) A amino acid B amylose C chlorophyll D DNA (b) Seedlings of rice plants were grown for two weeks in a complete solution containing all the mineral ions required. After two weeks, the plants were divided into three groups, A, B and C. • The plants in Group A were grown in a complete solution. • The plants in Group B were grown in a complete solution lacking magnesium ions. • The plants in Group C were grown in a complete solution lacking calcium ions. The plants were then grown for nine days. The diagrams show the plants at the end of the growing time. The labels L3 to L6 on the diagrams refer to the leaves in order of growth. L6 was the last leaf to grow. L3 Group A Group B Group C L3 L3 L4 L4 L4 L5 L5 L5 L6 L6 L6 At the end of the growing time, L5 was dead and L6 was yellow in the plants in Group B. Turn over 21 Comment on the effects of deficiencies in magnesium ions and calcium ions on the growth of these rice plants. (4) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 22 (c) ‘The growth of seedlings is affected by the concentration of magnesium ions whereas germination of seeds is not.’ Devise an investigation to obtain valid evidence to support this statement. 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(Total for Question 7 = 10 marks) Turn over 23 BLANK PAGE