PHYSIOLOGY OF EXCRETION -

1.      FORMATION OF UREA -

It takes place in liver.

(i) Deamination

(ii) Ornithine cycle or urea cycle -

• Explained by H. Kreb and Hansleit. 2 mol of NH₃, 1 CO₂, 2H2O combine to form urea as byproduct.
• 3 A.T.P. are consumed.
• Process takes place in five steps -

Enzyme used in five steps are -

1. Carbamyl phosphate synthatase                       

2. Ornithine carbamyl transferase.

3. Argino-succinic acid synthetase                       

4. Argio-succinase                                

5. Arginase