Rice, Oryza sativa, is an important food crop. Rice plants are wind pollinated. Pollen containing the male gamete is transferred by the wind to female reproductive organs of rice plants. Fertilisation and grain formation then occur. Weedy rice is a wild form of rice that grows in fields of cultivated rice. Weedy rice competes with cultivated rice for resources. Weedy rice plants are taller than cultivated rice plants and produce a low yield of rice grains. Several genetically modified (GM) varieties of cultivated rice have been developed. One concern about the use of GM rice is gene flow from GM rice plants to weedy rice. Gene flow occurs when the wind carries pollen from GM rice plants to weedy rice plants. Some scientists investigated gene flow from herbicide-resistant GM rice plants to weedy rice plants. The GM rice plants had a gene for herbicide resistance. Weedy rice plants do not have the gene for herbicide resistance. The scientists wanted to test the hypothesis that: Gene flow from GM rice to weedy rice decreases as the distance between the GM rice crop and weedy rice increases. The scientists planted GM rice and weedy rice in a field, as shown in Fig. 2.1. [Figure 2.1] Fig. 2.1 also shows that the wind normally blows in a north-west (NW) direction. After the plants had been pollinated and the rice grains had developed, the grains were collected from the weedy rice plants only. • Grains were collected from all weedy rice plants growing 1m from the GM rice plants in the directions N, NE, E, SE, S, SW, W and NW. • Grains were also collected in the same directions from the GM rice plants at distances of 2m, 5m and 10m. • Approximately 1000 grains from each collection point were planted and germinated in controlled conditions in a glasshouse. • The plants were grown for three weeks and then tested to determine whether they had the gene for herbicide resistance. Fig. 2.2 shows young rice plants three weeks after germination. [Figure 2.2]