4 2 Mineral ions are needed for plant growth. A student had a plant that had been kept in the same soil for a long time. The growth of the plant had slowed down and the leaves were pale green. The student decided to add fertiliser to the plant and measure the increase in height of the plant. The student made two predictions: • the leaves would gradually become greener • the plant would not start growing until the leaves were greener. (a) Explain why the student made these predictions. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (b) The student used a stock fertiliser solution at a concentration of 500 µg cm−3. Calculate the volumes of stock fertiliser solution and water that had to be mixed together to produce 100 cm3 of fertiliser solution at a concentration of 50 µg cm−3. (1) Volume of stock fertiliser solution .............................................................. cm3 Volume of water .............................................................. cm3 Turn over 5 (c) When the fertiliser was added to the plant, the height of the plant was 130 cm. Six weeks after the fertiliser was added, the plant had grown to a height of 155 cm. Calculate the mean growth rate for this plant, in centimetres per day, in this six-week period. (1) Answer .............................................................. cm day−1 (Total for Question 2 = 5 marks)