Lesson 15A.5

15A.5 Biological complexes: haemoglobin Quiz: Pearson Edexcel Chemistry, Unit 15

20 questions

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Lesson 15A.5, Biological complexes: haemoglobin: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 15: Transition Metals, written with Revision Ninja.

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The 20 questions

  1. Which metal ion is at the centre of the haem group in haemoglobin?

    • Copper
    • Magnesium
    • Zinc
    • Iron

  2. What is the oxidation state of the iron in haemoglobin that binds oxygen?

    • +1, as iron(I)
    • +4, as iron(IV)
    • +2, as iron(II)
    • +3, as iron(III)

  3. What type of bond forms between the iron centre and an oxygen molecule in oxyhaemoglobin?

    • A hydrogen bond between the oxygen and the protein
    • An ionic bond formed by transfer of electrons from iron to oxygen
    • A metallic bond with delocalised electrons
    • A dative bond, with O2 acting as a ligand that donates electron density to iron

  4. What is the role of the multidentate ligand in the haem group?

    • It converts iron(II) into iron(III) so that oxygen can bind more strongly to the haem group
    • It makes the iron a monodentate ligand, so that only one donor atom bonds to the oxygen molecule
    • It holds the iron firmly through several donor atoms, giving a stable complex
    • It prevents oxygen from reaching the iron centre by sitting in the only site that oxygen could use

  5. What is a ligand exchange reaction?

    • A reaction in which the metal ion changes its oxidation state and the ligands stay the same
    • A reaction in which a precipitate forms from two complex ions
    • A reaction in which a precipitate forms from two complex ions that exchange their ligands
    • A reaction in which the complex loses all of its ligands and becomes a bare metal ion

  6. In haemoglobin, which ligand is replaced by carbon monoxide in the ligand exchange?

    • Chloride, Cl-
    • Oxygen, O2
    • Ammonia, NH3
    • Water, H2O

  7. What is the main role of iron in haemoglobin's oxygen transport?

    • It is a catalyst that splits O2 into oxygen atoms
    • It stores electrons that are released to make ATP
    • It binds O2 reversibly
    • It dissolves CO2 so that it can be exhaled

  8. Which molecule is the ligand in oxyhaemoglobin?

    • CO2
    • H2O
    • N2
    • O2

  9. What is the approximate number of haem groups in one haemoglobin molecule?

    • Four
    • Two
    • Eight
    • One

  10. If the Fe(II) in haem is oxidised to Fe(III), what happens to oxygen transport?

    • It increases CO2 transport instead, because the oxidised iron binds carbon dioxide more strongly
    • It is unaffected, because the oxidation state does not matter to the binding of oxygen at all
    • It improves, because Fe(III) binds O2 more strongly and so carries more oxygen per haem group
    • It is impaired, because the iron(III) centre does not bind O2 in the same way

  11. Which equation represents ligand exchange when haemoglobin binds carbon monoxide?

    • Hb + O2 gives HbO2 + 2e-
    • Hb.O2 + CO gives Hb.CO + O2
    • Hb.CO gives Hb + CO2
    • Hb + H2O gives HbOH + H+

  12. Roughly how many times more strongly does CO bind to haemoglobin than O2?

    • About 200 times
    • About 2 times
    • About 20 times
    • About 2000 times

  13. A student says haemoglobin works because iron is a transition metal with a variable oxidation state. Which evaluation is best?

    • Incorrect, because haemoglobin contains no ligands and so cannot form any bonds to oxygen at all
    • Correct, because variable oxidation state alone explains oxygen transport in all living organisms
    • Partly correct, but the key is reversible binding of O2 to Fe(II) through the multidentate haem ligand
    • Incorrect, because iron plays no role in oxygen transport, which is carried out by the protein alone

  14. What is the name of the product formed when CO binds to haemoglobin?

    • Methaemoglobin
    • Carboxyhaemoglobin
    • Oxyhaemoglobin
    • Ferrihaemoglobin

  15. Why does plasma alone carry too little oxygen for the body's needs?

    • Haemoglobin stores oxygen as a solid crystal inside cells
    • Plasma cannot contain oxygen at all
    • O2 is more soluble in plasma than in haemoglobin
    • O2 has low solubility in plasma

  16. What does the term haem refer to in haemoglobin?

    • A protein chain that binds oxygen without any metal
    • A copper-containing unit that stores oxygen
    • A carbohydrate that transports oxygen in the blood
    • The iron-containing ring complex unit that binds oxygen

  17. The equilibrium Hb.O2 + CO gives Hb.CO + O2 lies far to the right. What does this mean?

    • Haemoglobin does not react with either gas
    • The reaction is reversible but lies far to the left
    • CO largely replaces O2 on haemoglobin
    • O2 largely replaces CO, so haemoglobin is cleared

  18. Why is the Fe(II)-haem complex described as a biological complex?

    • It contains no metal at all, so it is classified as an organic molecule rather than a complex
    • A metal ion bonded to ligands in a biological molecule forms a coordination complex that controls function
    • It is only formed in the laboratory and never in living cells, since no metal can bind to proteins
    • It is a covalent network like diamond, with each iron atom bonded to four others in a lattice

  19. What is the d-electron count of the Fe(II) centre in haem?

    • 8
    • 4
    • 5
    • 6

  20. What is the oxidation state of iron in methaemoglobin, the form in which iron is oxidised?

    • +3
    • +4
    • +2
    • +1

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