Final answer:
The term used to describe an organism that produces only purple-flowered offspring through self-pollination is true-breeding.
Step-by-step explanation:
The term used to describe an organism that produces only purple-flowered offspring through self-pollination is true-breeding. True-breeding organisms are genetically uniform and produce offspring with the same traits as themselves. In the case of the purple-flowered plant, it consistently passes on the purple flower trait to its offspring generation after generation.