| Date | May 2014 | Marks available | 2 | Reference code | 14M.3.hl.TZ2.9 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Describe | Question number | 9 | Adapted from | N/A |
Question
Hemoglobin is often described as a carrier of diatomic oxygen.
Describe the structure of hemoglobin.
Outline the role of hemoglobin in transporting diatomic oxygen.
Markscheme
(hemoglobin large protein molecule with) iron(II) held by four (nitrogen) ligands/coordinate/dative bonds (to form heme);
porphyrin/heme encapsulated in protein/polypeptide unit;
hemoglobin comprises four/several/more than one of these (protein/polypeptide) units;
(during respiration) oxygen bonds (temporarily) to iron (while hemoglobin travels through bloodstream releasing oxygen molecule when and where needed);
decreasing pH causes change in polypeptide releasing the oxygen;
each hemoglobin bonds to four oxygens;
iron stays in \( + 2\) oxidation state;
Examiners report
The structure of hemoglobin in Q9 was not well understood and its role in the transport of oxygen was superficial with very little mention of the change in pH. The question was based on B.9.2.
The structure of hemoglobin in Q9 was not well understood and its role in the transport of oxygen was superficial with very little mention of the change in pH. The question was based on B.9.2.
