This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of carbohydrate, Subject name: Biochemistry
Which of the following pathway occurs paly in mitochondria and paly in cytosol? 
Select and explain. 
A. Glycolysis, B. Kreb's cycle, C. Ketogenesis, D. Urea cycle
D: Urea cycle
Answer: D: Urea cycle 
Explanation: In mammals, the urea cycle takes place primarily in the liver, and to a lesser extent in the kidney. The urea cycle consists of five reactions: two mitochondrial and three cytosolic. The cycle conves two amino groups, one from NH4+ and one from Asp, and a carbon atom from HCO3-, to the relatively nontoxic excretion product urea at the cost of four "high-energy" phosphate bonds (3 ATP hydrolyzed to 2 ADP and one AMP). Ornithine is the carrier of these carbon and nitrogen atoms.Ref: DM Vasudevan, 7th edition, page no: 196,203,226