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Date May 2014 Marks available 2 Reference code 14M.3.hl.TZ2.9
Level HL Paper 3 Time zone TZ2
Command term Outline Question number 9 Adapted from N/A

Question

Hemoglobin is often described as a carrier of diatomic oxygen.

Describe the structure of hemoglobin.

[2]
a.

Outline the role of hemoglobin in transporting diatomic oxygen.

[2]
b.

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;

a.

(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;

b.

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.

a.

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.

b.

Syllabus sections

Options » B: Biochemistry » B.9 Biological pigments (HL only)
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