The control of BLOOD WATER POTENTIAL (OCR A-level Biology A)

This is a highly-detailed and fully-resourced lesson which covers the detail of specification point 5.1.2 (d) of the OCR A-level Biology A specification which states that students should be able to demonstrate and apply an understanding of the roles of the hypothalamus, posterior pituitary, ADH and the collecting duct in the control of the water potential of the blood. Students learnt about the principles of homeostasis and negative feedback in an earlier module, so this lesson acts to build on that knowledge and challenges them to apply their knowledge. A wide range of activities have been included in the lesson to maintain motivation and engagement whilst the understanding and prior knowledge checks will allow the students to assess their progress as well as challenge themselves to make links to other Biology topics.

The lesson begins with a discussion about how the percentage of water in urine can and will change depending on the blood water potential. Students will quickly be introduced to osmoregulation and they will learn that the osmoreceptors and the osmoregulatory centre are found in the hypothalamus. A considerable amount of time is taken to study the cell signalling between the hypothalamus and the posterior pituitary gland by looking at the specialised neurones (neurosecretory cells). Links are made to the topics of neurones, nerve impulses and synapses and the students are challenged to recall the cell body, axon and vesicles. The main section of the lesson forms a detailed description of the body’s detection and response to a low blood water potential. The students are guided through this section as they are given 2 or 3 options for each stage and they have to use their knowledge to select the correct statement. The final task asks the students to write a detailed description for the opposite stimulus and this task is differentiated so those who need extra assistance can still access the work.

This lesson has been written for students studying on the OCR A-level Biology A course and ties in nicely with the other uploaded lessons in module 5.1.2 which include the structure of the nephron, ultrafiltration and selective reabsorption.