AQA A Level Biology复习笔记3.4.7 Animal Adaptations For Their Environment

Different types of haemoglobin

• Haemoglobin is a quaternary protein made up of four globin polypeptides and four haem groups
• The structure of haem is identical in all types of haemoglobin but the globin chains can differ substantially between species
  • The globin polypeptides determine the precise properties of haemoglobin
• Haemoglobin types vary in their oxygen-binding properties, meaning that they bind to and release oxygen in different conditions
• Environmental factors can have a major impact on the evolution of haemoglobin within a species

Effects of altitude

• The partial pressure of oxygen in the air is lower at higher altitudes
• Species living at high altitudes have haemoglobin that is adapted to these conditions, e.g.
  • Llamas have haemoglobin that binds much more readily to oxygen
  • This is beneficial as it allows them to obtain a sufficient level of oxygen saturation in their blood when the partial pressure of oxygen (pO2) in the air is low

Species that live at high altitudes have evolved haemoglobin with a higher affinity for oxygen; this means that at any given partial pressure of oxygen the high altitude haemoglobin has a higher percentage saturation than lower altitude haemoglobin

Foetal haemoglobin

• The haemoglobin of a developing foetus has a higher affinity for oxygen than adult haemoglobin
• This is vital as it allows a foetus to obtain oxygen from its mother's blood at the placenta
  • Fetal haemoglobin can bind to oxygen at low pO2
  • At this low pO2 the mother's haemoglobin is dissociating with oxygen
• On a dissociation curve graph, the curve for foetal heamoglobin shifts to the left of that for adult haemoglobin
  • This means that 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

Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin. This means that at any given pO2, foetal haemoglobin will have a higher percentage saturation than adult haemoglobin.