Haemoglobin & the Bohr effect (Edexcel Int. A-level Biology)

This lesson describes the role of haemoglobin in transport and explains the change in the dissociation curve when there is an increased concentration of carbon dioxide (the Bohr effect). The detailed PowerPoint and accompanying resources have been designed to cover points 1.9 (i) & (ii) of the Edexcel International A-level Biology specification and this lesson also compares the oxyhaemoglobin dissociation curve of foetal haemoglobin against maternal haemoglobin.

The lesson begins with a version of the quiz show Pointless and this introduces haemotology as the study of the blood conditions. Students are told that haemoglobin has a quaternary structure as it is formed of 4 polypeptide chains which each contain a haem group with an iron ion attached and that it is this group which has a high affinity for oxygen. Time is taken to discuss how this protein must be able to load (and unload) oxygen as well as transport the molecules to the respiring tissues. Students will plot the oxyhaemoglobin dissociation curve and the S-shaped curve is used to encourage discussions about the ease with which haemoglobin loads each molecule. At this point, foetal haemoglobin and its differing affinity of oxygen is introduced and students are challenged to predict whether this affinity will be higher or lower than adult haemoglobin and to represent this on their dissociation curve.
Moving forwards, the different ways that carbon dioxide is transported around the body involving haemoglobin are described and the dissociation of carbonic acid into hydrogen ions is discussed so that students can understand how this will affect the affinity of haemoglobin for oxygen in the final part of the lesson on the Bohr effect. A quick quiz is used to introduce Christian Bohr and the students are given some initial details of his described effect. This leads into a series of discussions where the outcome is the understanding that an increased concentration of carbon dioxide decreases the affinity of haemoglobin for oxygen. The students will learn that this reduction in affinity is a result of a decrease in the pH of the cell cytoplasm which alters the tertiary structure of the haemoglobin. The lesson finishes with a series of questions where the understanding and application skills are tested as students have to explain the benefit of the Bohr effect for an exercising individual.