The kidneys FILTER the blood and remove things that should not be there or that there is too much of. UREA, GLUCOSE,WATER, AND MINERAL IONS diffuse across the partially permeable membrane. The urea is all filtered out of the blood and is URINATED out along with any EXCESS water and mineral particles, but the GLUCOSE is all reabsorbed into the blood by active transport because it is needed for respiration. Some water and mineral ions are also reabsorbed to be used by the body.
RED BLOOD CELLS and PROTEINS are too big to fit through the walls of the nephrons that the capillaries are near to, so they cannot diffuse out of the blood like urea, glucose, water and minerals can :)
Key Words
UREA Bad stuff that is toxic to the body, all of it is removed and urinate
PARTIALLY PERMEABLE MEMBRANE - wall that has very small holes in, only very small molecules can fit through using diffusion, osmosis or active transport
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