This lesson describes how the loop of Henle acts as a countercurrent multiplier to increase the reabsorption of water. The PowerPoint and accompanying resource are part of the 2nd lesson in a series of 2 lessons which have been designed to cover point 9.9 (iii) of the Edexcel A-level biology B specification but also considers the structure of the kidney in the kangaroo rat and therefore also covers point 9.9 (v).
The lesson begins by challenging the students to recognise that the glomerular filtrate entering the loop will only contain water, ions and urea if the kidneys are functioning properly. Time is then taken to look at the structure of the loop of Henle, focusing on the descending and ascending limbs, and their differing permeabilities. Students will be reminded that this part of the nephron is located in the renal medulla, before a step-by-step guide is used to describe how the transfer of ions, particularly sodium ions, from the ascending limb to the descending limb, creates a very negative water potential in this region of the kidney. This allows water to move out of the descending limb to the tissue fluid and then into the capillaries.
The next part of the lesson challenges students to consider the bigger picture as they learn that this decreasing water potential in the medulla allows water to be reabsorbed from the filtrate in the collecting duct too.
The remainder of the lesson uses the real-world examples of the hopping mouse and kangaroo rat to check student understanding, and there are also prior knowledge checks to encourage students to make links to relevant content from earlier topics. All answers are embedded into the PowerPoint.
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