Cats were fasted overnight then given a single meal complete in all amino acids except arginine. Within 2 hours, blood ammonia levels increased from a normal level of 18 μg/L to 140 μg/L, and the cats showed the clinical symptoms of ammonia toxicity. A control group fed a complete amino acid diet showed no unusual clinical symptoms.

(a) What was the role of fasting in the experiment?
(b) What caused the ammonia levels to rise in the experimental group?
(c) Why did the absence of arginine lead to ammonia toxicity?