We take stomata for granted – they’re on every leaf around us, and without them the world wouldn’t breathe. They don’t just respond to daylight and atmospheric humidity: new research shows that plants slam their stomata shut against invading bacteria.

But when and how did this complex ability evolve? The fossil record leaves us with a fascinating puzzle. In this 5 minute talk, Professor Alistair Hetherington of Bristol University discusses the mysterious evolution of stomata.

The accompanying notes include a teachers' summary, plus student questions and answers.