This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
The vitamin B6 contained in plants is less bioavailable than that in animal tissues. Pyridoxine is required for: 
Select and explain. 
A. Urea formation, B. Heme synthesis, C. Amylase, D. Lipoprotein lipase
B: Heme synthesis
Answer: B: Heme synthesis 
Explanation: Pyridoxine (Vitamin B6): Vitamin B6 refers to a family of compounds that include pyridoxine, pyridoxal, pyridoxamine, and their 5'-phosphate derivatives. 5'-Pyridoxal phosphate (PLP) is a cofactor for enzymes that involved in amino acid metabolism. Vitamin B6 also is involved in heme and neurotransmitter synthesis and in the metabolism of glycogen, lipids, steroids, sphingoid bases, and several vitamins, including the conversion of tryptophan to niacin. Severe vitamin B6 deficiency can lead to, Peripheral neuropathy Abnormal electroencephalograms Personality changes that include depression and confusion. Ref: Russell R.M., Suter P.M. (2012). Chapter 74. Vitamin and Trace Mineral Deficiency and Excess. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.