Base your answer to the question on the graph below and on your knowledge of Earth science. The graph shows the number of radioactive Isotope X atoms present as a sample of the isotope undergoes radioactive decay.

The structures are nephrons which gets blood through the [renal artery]. The nephrons also consist of the [afférent and efferent artérioles], the latter of which is much narrower causing a high pressure to exist in the [glomerulus] (blood vessels in that ball structure) so that ultrafiltration can occur and the ultrafiltrate is passed into the [Bowman’s capsule]. The Bowman’s capsule consists of podocytes which are cells that form a microscopic pore so that small molecules can pass through (ions and such). There is the [proximal convoluted tube] that makes the contents flow downwards (and allows water to exit so the water potential inside is low) and the [distal convoluted tube] that makes the contents go upwards (and allows water to re-enter which increases the water potential inside). These are both partially permeable and set up a concentration gradient for the reabsorption of water from the urine. These tubes lead into the [collecting duct] which further reabsorb the water.

All the structures of the kidney are in [ ].