Haemoglobin, the Dissociation Curve and the Bohr Shift · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

How haemoglobin loads and unloads oxygen

Science · The Human Body · ages 17-18
Name ______________________   Date ____________

  1. Where does haemoglobin load up with oxygen fastest?

    • In resting tissue, where pressure is lowest
    • In the lungs, where oxygen pressure is high
    • In the veins, where blood runs darkest

  2. How many oxygen molecules can a single haemoglobin molecule carry?

    • Four
    • One
    • Two

  3. What makes the dissociation curve S-shaped rather than straight?

    • Red cells changing shape in narrow vessels
    • Oxygen dissolving directly in the plasma
    • Cooperative binding after the first oxygen attaches

  4. After a rightward shift, what does haemoglobin hold at the same oxygen pressure as before?

    • More oxygen than before
    • Less oxygen than before
    • No oxygen at all

  5. A muscle works hard and carbon dioxide builds up around it. Which way does its curve move?

    • It shifts to the right, favouring unloading
    • It shifts to the left, gripping oxygen tighter
    • It stays fixed, since only pressure matters

  6. At very high pressure the curve flattens near the top. What does that tell you?

    • Haemoglobin has stopped working entirely
    • Oxygen has run out in the lungs
    • Haemoglobin is nearly fully loaded, so extra pressure adds little

  7. Failing kidneys let acid build up so blood pH drops. What happens to oxygen delivery?

    • Affinity rises, so haemoglobin refuses to release oxygen
    • Affinity falls, so tissues unload oxygen more easily
    • Nothing changes, since pH never affects binding

  8. A student says carbon dioxide shifts the curve left so muscle keeps its oxygen. What is wrong?

    • Both the direction and the effect are backwards
    • Curves can never shift in either direction
    • Carbon dioxide has no link to oxygen release
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Answer key

For grown-ups. Fold this page away before handing over the rest.

How haemoglobin loads and unloads oxygen W1-mt_MmYJArGxrE-s1

  1. In the lungs, where oxygen pressure is high · High pressure in the lungs drives oxygen onto haemoglobin.
  2. Four · Haemoglobin has four subunits and each binds one oxygen molecule.
  3. Cooperative binding after the first oxygen attaches · Each oxygen twists haemoglobin so the next binds more easily, steepening the middle.
  4. Less oxygen than before · Right means lower saturation at any pressure, which is more oxygen released.
  5. It shifts to the right, favouring unloading · Carbon dioxide produces the Bohr shift to the right, releasing oxygen where it is needed.
  6. Haemoglobin is nearly fully loaded, so extra pressure adds little · On the flat top almost every spot is filled, leaving little room for more.
  7. Affinity falls, so tissues unload oxygen more easily · Lower pH loosens the grip like carbon dioxide does, favouring unloading.
  8. Both the direction and the effect are backwards · Carbon dioxide shifts the curve right, which releases oxygen rather than keeping it.
Worksheet · LightMySky