2.68a excretion

• urea contains nitrogen which is toxic
• amino acids (that are used for growth) contain nitrogen but excess AA have to be excreted
• the amino acids circulates to the the liver and urea comes out which re-enters into the bloodstream which circulates to both kidneys so that the kidneys can filter the urea from the blood which is added to the water to create urine which circulates to the bladder.

this is an example of excretion.