26   10 All mammals have an internal skeleton that includes bone and cartilage. Bones contain calcium ions. (a) Explain one way in which cartilage at the ends of the bones in the knee joint reduces wear and tear. 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(b) In humans, calcium ions are important for structure as part of bone material. These ions are also involved in physiological processes in soft tissue. Soft tissue is non‑bony material. The table shows some data relating to humans. mean mass of an adult 80 kg mean percentage of body mass that is bone 4% mean mass of calcium ions per adult 1000 g mean percentage of calcium ions present in soft tissue 1% (i) Calculate the calcium ion concentration in the soft tissue of a human. (3) .............................................................. µg g–1 Turn over 27   *(ii) Calcium ions are also found in the tissue of plants. The calcium ion concentration in one species of plant has been measured. It was found to be 170 µg g–1 of plant tissue. A student made the conclusion that: Calcium ions are more important in the tissue of plants than in animals. Evaluate this conclusion. 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.................................................................................................................................................................................................................................................................................... 28   (c) Milk from humans contains both calcium ions and lactose. Lactose is a disaccharide. Describe how lactose is formed from two monosaccharides. 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(Total for Question 10 = 13 marks) TOTAL FOR PAPER = 100 MARKS