Hydroponics is a technique used to grow plants without soil. The diagram shows plants being grown using hydroponics. [Figure 4.1: Diagram showing a hydroponics setup with nutrient solution, air pump, air stone, growing tray, plants, light source, and timer.]

1. (a)The leaves of the plants are provided with a source of light for photosynthesis. State, in either words or symbols, the equation for photosynthesis.[2]
2. (b)The roots of the plants are provided with a nutrient solution. The nutrient solution contains magnesium ions. Air is pumped through the nutrient solution using an air stone that contains many very small holes.
3. (b)(i)Explain the advantage to the cells of the plant roots of pumping air through the nutrient solution using the air stone.[4]
4. (b)(ii)State the type of cell in plant roots that absorbs magnesium ions from the solution.[1]
5. (b)(iii)State the process that transports magnesium ions against a concentration gradient into this type of cell.[1]
6. (c)Farmers grew groups of 20 tomato plants for the same length of time in nutrient solutions with a range of different concentrations of magnesium ions. They determined the best concentration of magnesium ions for growth by measuring the following for each group of 20 tomato plants: • the mean height of the tomato plant stems (cm) • the mean mass of the tomato plant stems and leaves (g). The results of the investigation are shown in the table. [Table data: concentration of magnesium ions /parts per million (0, 50, 125, 250, 500), mean height of tomato plant stems /cm (20.0, 30.3, 32.6, 23.4, 20.4), mean mass of tomato plant stems and leaves /g (6.3, 11.7, 12.3, 10.4, 8.0)]
7. (c)(i)State the best concentration of magnesium ions for growth. parts per million[1]
8. (c)(ii)Explain your answer using the results of the investigation and your knowledge of the importance of magnesium ions to plants.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.