3.4.1 Mass Transport in animals

• Arteries and arterioles take blood away from the heart. Explain how the structures of the walls of arteries and arterioles are related to their functions. [6 marks]

  • Elastic tissue stretches under pressure / when heart beats then recoils / springs back
  • Evens out pressure / flow;
  • Muscle contracts to reduce diameter of lumen / vasoconstriction / constricts vessel;
  • Changes flow / pressure
  • Epithelium smooth
  • Reduces friction / blood clots / less resistance;
• Describe the role of red blood cells and haemoglobin in oxygen transport

  ● Red blood cells contain lots of haemoglobin (Hb) - no nucleus, biconcave, high surface area : volume ratio , short diffusion path

  ● Hb associates with / binds / loads O2 at gas exchange surfaces where partial pressure of O2 (pO2) is high

  ● This forms oxyhaemoglobin which transports O2 (each can carry 4O2 - one at each Haem group)

  ● Hb dissociates from / unloads O2 near cells / tissues where pO2 is low
• Describe the structure of haemoglobin

  ● Protein with a quaternary structure

  ● Made of 4 polypeptide chains

  ● Each chain contains a Haem group containing an iron ion (Fe2+)
• The haemoglobins are a group of chemically similar molecules found in many different organisms.
• Describe the loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve

  Areas with low pO2 (respiring tissues):

  ● Hb has a low affinity for O2

  ● So O2 readily unloads / dissociates with Hb

  ● So % saturation is low
• Describe the loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve

  Areas with high pO2 (gas exchange surfaces):

  ● Hb has a high affinity for O2

  ● So O2 readily loads / associates with Hb

  ● So % saturation is high

  
• Explain how the cooperative nature of oxygen binding results in an S-shaped (sigmoid) oxyhaemoglobin dissociation curve

  1. Binding of first oxygen changes tertiary / quaternary structure of haemoglobin

  2. This uncovers Haem group binding sites, making further binding of oxygens easier
• Describe evidence for the cooperative nature of oxygen binding

  ● A low pO2 as oxygen increases there is little / slow increase in % saturation of Hb with oxygen

  ○ When first oxygen is binding

  ● At higher pO2 , as oxygen increases there is a big / rapid increase in % saturation of Hb with oxygen

  ○ Showing it has got easier for oxygens to bind
• What is the Bohr effect?

  Effect of CO2 concentration on dissociation of oxyhaemoglobin → curve shifts to right
• Explain effect of CO2 concentration on the dissociation of oxyhaemoglobin

  1. Increasing blood CO2 eg. due to

  increased rate of respiration

  2. Lowers blood pH (more acidic)

  3. Reducing Hb’s affinity for oxygen as

  shape / tertiary / quaternary

  structure changes slightly

  4. So more / faster unloading of oxygen

  to respiring cells at a given pO2

  
• How the curve provides evidence for Bohr effect

  • At a given partial pressure of oxygen, percentage saturation of Haemoglobin is lower

  
• Explain the advantage of the Bohr effect (eg. during exercise)

  • More dissociation of oxygen
  • faster aerobic respiration / less anaerobic respiration →
  • more ATP produced
• Explain how organisms can be adapted to their environment by having different types of haemoglobin with different oxygen transport properties

  Curve shift left → Hb has higher affinity for O2

  ● More O2 associates with Hb more readily

  ● At gas exchange surfaces where pO2

  is lower

  ● Eg. organisms in low O2 environments -

  high altitudes, underground, or foetuses
• Curve shift right → Hb has lower affinity for O2

  ● More O2 dissociates from Hb more readily

  ● At respiring tissues where more O2 is needed

  ● Eg. organisms with high rates of respiration / metabolic rate (may be small or active)