The diagram shows a pollen grain with a pollen tube growing from it. [Diagram of pollen grain with pollen tube] Pollen grains from the same type of plant were placed in sucrose solutions of different concentrations for a fixed amount of time. After this time, the pollen grains and tubes were examined using a microscope. The following observations were made for each concentration of sucrose: : the number of pollen grains that had germinated to produce a pollen tube, the length of each pollen tube. The table shows the results of the investigation. | % sucrose concentration | % of pollen grains germinated | mean pollen tube length/mm | |---|---|---| | 1 | 6 | 0.005 | | 2 | 13 | 0.008 | | 4 | 25 | 0.015 | | 8 | 56 | 0.040 | | 10 | 31 | 0.030 | | 20 | 25 | 0.018 | | 40 | 13 | 0.006 |

1. (a)(i)A total of 12 pollen grains were placed in the 20% sucrose solution. Use the information in the table to calculate the number of pollen grains that germinated to produce a pollen tube in the 20% sucrose solution.[1]
2. (a)(ii)Suggest why the mean pollen tube length was calculated for each sucrose concentration.[1]
3. (a)(iii)Use the information in the table to suggest the optimum (best) concentration of sucrose solution for pollen tube germination and growth. % Explain how the information in the table enabled you to reach this conclusion.[3]
4. (a)(iv)The germination of a pollen grain to form a pollen tube requires the movement of water into the pollen grain from its surroundings. Suggest why placing a pollen grain in a solution with a higher sucrose concentration than in your answer to (a)(iii) may result in a lower percentage of germination.[3]
5. (b)Describe the route taken by a growing pollen tube in a plant and explain its importance in plant reproduction.[4]

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