(a) Haemoglobin is a globular protein which is able to transport oxygen and is soluble in water.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

1. [3] (a)(i) any three from haem group containing iron (atom);
2. [3] (a)(i) four haem groups (per molecule of haemoglobin);
3. [3] (a)(i) each iron (atom) / haem / prosthetic group, binds one oxygen molecule ; or four oxygen molecule per haemoglobin molecule ;
4. [3] (a)(i) cooperative binding / allosteric effect described ;
5. [3] (a)(i) AVP;
6. [2] (a)(ii) any two from ref. folding of polypeptide chain(s) / globin(s) fold (to give globular structure) ; A ref. to, tertiary structure / quaternary structure
7. [2] (a)(ii) (so) hydrophilic R groups (of amino acids) are on the outside of the molecule / hydrophobic R groups (of amino acids) on the inside of the molecule;
8. [2] (a)(ii) A hydrophilic and hydrophobic amino acids
9. [2] (a)(ii) hydrogen bonds form with water (molecules) ;
10. [1] (b)(i) Ilama = 90.5% human = 78.5% ;
11. [2] (b)(ii) any two from lower partial pressure of oxygen at high altitude ;
12. [2] (b)(ii) at the same partial pressure the percentage saturation is (much) higher than for humans ;
13. [2] (b)(ii) ref. to haemoglobin has a higher affinity for oxygen ;
14. [2] (b)(ii) idea that sufficient oxygen delivered to tissues to satisfy demand;