Problem solving is an ideal learning strategy, especially for topics that are perceived as difficult to teach. As an example, a format is described for a problem-solving session designed to help students understand the pressure-flow hypothesis of phloem transport in plants. Five key facts and their discussion can lead to the conclusion that a turgor-pressure difference along sieve tubes of the phloem drives a mass flow of sugar solution between source and sink. The given format is suitable for use in the sixth-form classroom when the mechanism of phloem transport is usually first taught to students. Additional information is provided so that school teacher scan lead a class discussion and stimulate student interest in the phloem as a long-distance transport system. (Contains 1 box.)