Final answer:
The breakdown of the non-iron portion of heme in the correct sequence is Biliverdin → Bilirubin → Urobilinogen → Stercobilinogen, best represented by option A in the given choices.
Step-by-step explanation:
The correct sequence in the breakdown of the non-iron portion of the heme is Biliverdin → Bilirubin → Urobilinogen → Stercobilinogen, which corresponds to option A. This breakdown process starts with the degradation of the non-iron portion of heme into biliverdin, a green pigment, which is further reduced to bilirubin, a yellow pigment. In the liver, bilirubin is used in the manufacture of bile and then passes into the intestines. In the large intestine, bilirubin is transformed by bacteria to urobilinogen, and some of it is further converted into stercobilinogen before being excreted as stercobilin in the feces, giving it its characteristic brown color.