A detailed study of the way our kidneys work is confined to KS4 and A-level science courses. But KS3 pupils need to know where the kidneys are, how many they have and their relationship to other body structures. This is best done with a model torso that shows their positioning on either side of the main artery and vein on the back wall of the abdomen, and the tube going from each kidney to the bladder.
lUsing an untrimmed lamb's kidney from a butcher shop, slice it in half lengthwise to show the exterior (cortex), the darker medulla towards the inside and the white part, which collects urine before it is discharged into the tube (ureter) that goes to the bladder. The branching shape of this white part is easy to see.
lA kidney is made up of thousands of tiny tubes (nephrons), each with their own blood supply. Sixth-formers could inject the artery of a lamb's kidney with warm liquid latex, allow it to cool and then slice the kidney to reveal the branching pattern of the blood vessels. A kidney prepared in this way could be used at KS4 to show the branching of the artery inside the kidney. This injection technique is described in Biology: A Functional Approach: Student's Manual by Michael Roberts and Tim King (Nelson Thornes, pound;20.50). It can also be used to show the branch tubes that join up to form the ureter and those that unite to form the vein.
lStudents may know that when they drink a lot they expel large volumes of pale yellow urine. If they sweat a lot and don't drink, there is less urine and it is a darker colour. The deeper the colour, the more concentrated it is. It is difficult to investigate this in school, so use the tables of data about the body's water intake that are in most school texts.