Answer 1

The main nitrogenous waste in the human blood is urea. The kidneys remove the urea from the blood and excrete them in the form of a dilute solution called urine. 
Kidneys are the main excretory organ of the human body. There are millions of nephrons in each kidney. Each nephron contains a renal corpuscle and a renal tubule. The renal corpuscle consists of capillaries called the glomerulus, enclosed by a capsule called Bowman's capsule. The blood is filtered in the glomerulus and the filtrate travels through the renal tubules. Here, the materials needed by the body are reabsorbed, while the wastes (like urea) are collected and excreted in the urine.