Osmosis and water potential (WJEC A-level Biology)

This lesson describes the transport mechanism of osmosis as the movement of water molecules from a high water potential to a lower water potential. The PowerPoint and accompanying resources are part of the second lesson in a series of 4 lessons which have been designed to cover point [c] as detailed in AS unit 1, topic 3 of the WJEC A-level Biology specification and also describes how cells are affected by this movement of water

It’s likely that students will have used the term concentration in their osmosis definitions at GCSE, so the aim of the starter task is to introduce water potential to allow students to begin to recognise osmosis as the movement of water molecules from a high water potential to a lower potential, with the water potential gradient. Time is taken to describe the finer details of water potential to enable students to understand that 0 is the highest value (pure water) and that this becomes negative once solutes are dissolved. Exam-style questions are used throughout the lesson to check on current understanding as well as prior knowledge checks which make links to previously covered topics such as the lipid bilayer of the cell membrane. The remainder of the lesson focuses on the movement of water when animal and plant cells are suspended in hypotonic, hypertonic or isotonic solutions and the final appearance of these cells is described, including any issues this may cause.