What is meant by excretion? Explain the process of formation of urine (AS1)

Excretion of the process of elimination of waste products produced by the organism into its surrounding.

The formation of urine takes place in two steps:

i. Ultracentrifugation: The blood flows through the glomerulus under very high pressure which causes the liquid part of the blood to filter out from the glomerulus into the renal tubules. This filtration under extraordinary force is called ultrafiltration.

ii. Reabsorption: The glomerular filtrate entering the renal tubule is not urine. As this filtrate passes down the tubule most of the water is reabsorbed with the reusable substances. This process concentrates the glomerular filtrate finally forming urine.