Rod cells in the retina (Edexcel A-level Biology A)

This fully-resourced lesson describes how rod cells in the mammalian retina detect stimuli to allow vision in low light intensity. The detailed PowerPoint and accompanying resources have been designed to cover the second part of point 8.5 of the Pearson Edexcel A-level Biology A (Salters Nuffield) specification and includes reference to the roles of rhodopsin, opsin, retinal, sodium ions, cation channels and hyperpolarisation in the formation of action potentials in the optic neurones.

It is likely that students will be aware that the human retina contains rod and cone cells, so this lesson builds on that knowledge and adds the detail needed at this level. Students will discover that the optical pigment in rod cells is rhodopsin and that the bleaching of this into retinal and opsin results in a cascade of events that allows an action potential to be initiated along the optic nerve. Time is taken to go through the events that occur in the dark and then the students are challenged to use this as a guide when explaining how the events differ in the light. Key terms like depolarisation and hyperpolarisation, that were met earlier in topic 8, are used to explain the changes in membrane potential and the resulting effect on the connection with the bipolar and ganglion cells is then described.