Smilax china is a herbaceous plant. Fig. 1.1 shows part of a transverse section of a root of S. china with root hair cells visible. [Figure 1.1]

1. (a)Name the type of microscope that has been used to obtain the image in Fig. 1.1.[1]
2. (b)Calculate the actual length, in micrometres (µm), of the root hair cell labelled in Fig. 1.1. Use the image length of the root hair cell along line X–Y in your calculation. actual length =[1]
3. (c)Root hairs are important adaptations of root hair cells for the uptake of water. Explain one way in which root hairs adapt root hair cells for the uptake of water.[1]
4. (d)Mineral ions are taken up by root hair cells. Table 1.1 shows the concentrations of sodium ions (Na+) and potassium ions (K+) inside the root hair cells of a plant root and in the soil solution surrounding the root. Table 1.1 concentration of Na+/g dm⁻³ root hair cell 0.35 soil solution 3.34 concentration of K+/g dm⁻³ root hair cell 5.46 soil solution 0.16 With reference to Table 1.1: • suggest the mechanisms involved in the transport of Na+ and K+ from the soil solution into the root hair cells • state the reasons for your suggestions.[3]
5. (e)The region between the outer layer of a root and the endodermis is known as the cortex. Table 1.2 shows the water potential of two adjacent cells, A and B, in the cortex of a root. Table 1.2 water potential/kPa cortex cell A −120 cortex cell B −350 With reference to Table 1.2, explain the direction of water movement between cell A and cell B.[2]
6. (f)(i)Some types of soil are made of small negatively charged clay particles that attract and bind to positive ions such as iron ions (Fe2+). Fe2+ that is bound to clay particles cannot be absorbed by root hair cells. This reduces the concentration of free Fe2+ that is available in soil solution for absorption. Some plants that grow in soils containing a high proportion of clay particles are able to increase the concentration of free Fe2+ in the soil solution for absorption. In these plants, the carbon dioxide released by the respiration of root hair cells reacts with water in the soil solution, which changes the pH of the soil solution. This affects the binding of positively charged ions, such as Fe2+, to clay particles. Fig. 1.2 shows the results of one investigation into the effect of pH on the concentration of free Fe2+ that is available in soil solution for absorption by root hair cells. The soil sample analysed in this investigation was from a soil that contained a high proportion of clay particles. [Figure 1.2] With reference to Fig. 1.2, suggest and explain how the carbon dioxide released by the respiration of root hair cells can increase the concentration of free Fe2+ for absorption by root hair cells.[4]
7. (f)(ii)Dissolved Fe2+ is transported across the tissues of the root to the xylem. When the amount of dissolved Fe2+ absorbed by root hair cells is greater than the amount that is needed by the plant, not all of the Fe2+ that is absorbed is transported to the xylem. Suggest how the endodermis can reduce the amount of Fe2+ reaching the xylem.[3]

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