CBSE Class 10 Answered

The filtration unit in human kidneys is the nephrons. More specifically, it is the glomerulus of nephrons which carry out this function of filtration of blood.

Malpighian tubule shows a cup shaped Bowman's capsule and a tuft of blood capillaries called glomerulus fitted into the cavity of the Bowman's capsule. These capillaries connect the 2 branches of renal artery, the afferent arteriole (that brings in blood) and an efferent arteriole (that drains blood away from the glomerulus). The diameter of afferent arteriole is greater than that of the efferent, hence blood flows under great pressure in the glomerulus.

Ultra- filtration occurs in the malpighian body. It is the filtration of blood under pressure. Here, blood is filtered so finely that almost all the constituents of the plasma, except the proteins pass onto the lumen of the Bowman's capsule from the glomerulus. Blood pressure forces water and small molecules to be filtered from the glomerulus and collected in Bowman's capsule. The filtrate formed by ultra filtration is the primary urine.