You can see this on the BBC Four Botany: A Blooming History for a clear picture when using with students.

This video clip from the BBC (from the TV series Botany: A Blooming History) looks at the case for genetic modification of crop plants, and could be used for a useful stimulus for a class discussion.

The case is made for genetic modification of plants in the context of the thousands of year over which we have selected and cross-bred plants for food. Now we are faced with pests and diseases which our crop plants are not resistant to and hence yield falls. Modifying plant genomes so that the plants develop resistance would increase the chances of producing enough food for our growing population.

This would be a stimulus for a class discussion of G.M. crop plants. Students could research the arguments for and against genetic modification and the risks associated with it. Debates could include the questions of whether the research is necessary, whether the risks are too great or whether the risks outweigh the benefits.