Adaptations in Haemoglobin (AQA AS Biology): Revision Note

Types of haemoglobin

• Different organisms may have different types of haemoglobin that bind to and release oxygen in different environmental conditions

  • These differences arise through the process of natural selection

• Examples of organisms that may have specialised haemoglobin include those that:

  • live in low pO₂ environments

    • Haemoglobin needs to pick up oxygen at a pO₂ at which adult human haemoglobin would release it

    • Haemoglobin needs a higher affinity for oxygen

  • are highly metabolically active, e.g. due to being small in size and needing to generate body heat

    • Haemoglobin needs to release oxygen easily to respiring tissues

    • Haemoglobin needs a lower affinity for oxygen

Haemoglobin at low pO₂

At high altitude

• The partial pressure of oxygen (pO₂) in the air is lower at higher altitudes

• Species living at high altitudes have haemoglobin that is adapted to these conditions by having an increased affinity for oxygen, e.g.:

  • llamas have haemoglobin with a high affinity for oxygen; it binds more readily to oxygen, allowing them to obtain a sufficient level of oxygen saturation in their blood when the pO₂ in the air is low

• Oxyhaemoglobin dissociation curves for haemoglobin with a higher affinity for oxygen shift to the left

In the developing fetus

• During development a fetus gains its oxygen from the mother's blood, which has already travelled around the body and so has a low pO₂

• The haemoglobin of a developing foetus therefore has a higher affinity for oxygen than adult haemoglobin, so that it can obtain oxygen from its mother's blood at the placenta

  • At this low pO₂ the mother's haemoglobin is dissociating with oxygen

• The dissociation curve for fetal haemoglobin shifts to the left of that for adult haemoglobin

  • At any given partial pressure of oxygen, foetal haemoglobin has a higher percentage saturation than adult haemoglobin

• After birth, a baby begins to produce adult haemoglobin which gradually replaces foetal haemoglobin

  • This is important for the easy release of oxygen in the respiring tissues of a more metabolically active individual