Role of plant hormones (OCR A-level bio)

This lesson describes the role of plant hormones in stomatal closure, leaf loss in deciduous plants and seed germination. The extensive and detailed PowerPoint and accompanying resources have been planned to cover the content of point b of module 5.1.5 of the OCR A-level biology A specification.

The start of the lesson challenges the students to identify three leaf cells in the list of 11 leaf structures. This introduces guard cells and then the opening between them, the stomatal aperture. Time is taken to go through the process by which the apertures are opened to allow carbon dioxide to diffuse into the leaf for photosynthesis. This provides students with an insight into the movement of potassium ions and water when they are challenged about the closure of these openings in response to water stress. Students will meet abscisic acid and understand how this acts as the first messenger, before calcium ions act as the second messenger to trigger events on the inside of the guard cells.

Moving forwards, the role of ethene and auxins in leaf loss and gibberellins in seed germination are described and explained. Multiple opportunities are taken to challenge students on their prior knowledge as well as their current understanding and all answers are embedded into the PowerPoint.

This lesson is extensive and it is estimated that it will take 2-3 hours of teaching time to go through all of the tasks and content.