Mass transport

    Cards (47)

    • Larger organisms

      • Need specialised exchange surfaces to absorb nutrients, exchange respiratory gases and excrete waste products
      • Need specialised transport systems to transport materials between the cells and the exchange surfaces
    • Larger organisms with a smaller surface area to volume ratio, that are more active

      • Have a greater need for a specialised transport system with a pump
    • Transport medium
      Normally water-based liquid (water acts as a solvent and can be moved around easily) but can be a gas
    • Closed system of tubular vessels
      • To contain the transport medium and to form a branched network to deliver it to all tissues within the organism
    • Mechanism for moving the transport medium within the vessels
      • This is generated by creating pressure differences between one part of the system and another
      • In animals: created by muscles contracting/the heart acting as a pump
      • In plants: created by passive processes such as loading of sugar into phloem/evaporating of water in leaves
    • Mechanism to maintain the mass flow movement in one direction
      • Normally controlled by valves preventing the backflow of the medium
    • Circulatory systems in mammals
      • Double (passes twice through the heart for each complete loop of the body)
      • Closed (blood is confined to vessels)
    • If blood was pumped straight from the lungs to the rest of the body, the pressure would be too low and circulation would be too slow
    • Transport systems are used to move substances long distances in organisms, but the final phase is diffusion through the tissue fluid
    • Diffusion into cells
      • Large surface area
      • Short diffusion distance
      • Steep concentration gradient
    • Haemoglobins
      Quaternary proteins that have evolved to load (bind to) oxygen under certain conditions but unload (release) oxygen under a different set of conditions
    • Different organisms have haemoglobins with a slightly different amino acid sequence. This changes the tertiary structure of their polypeptide chains, changing the quaternary structure and giving them different oxygen binding properties
    • Primary structure
      2α & chains of amino acids in human adult haemoglobin
    • Secondary structure
      Each chain is folded into a 3D shape that allows it to carry one oxygen molecule
    • Tertiary structure

      All 4 chains are linked & each is associated with a haem group. The Fe2+ ion can combine with a single oxygen molecule (O2)
    • Quaternary structure
      Each chain is coiled into a helix
    • Role of Haemoglobin
      To transport oxygen: Readily associate with oxygen where gas exchange takes place, Readily dissociate with oxygen at respiring tissues
    • Partial pressure (relative conc) of Oxygen
      High at gas exchange surface (alveoli in lungs), Low at respiring tissues (contracting muscles)
    • Partial pressure (relative conc) of Carbon Dioxide
      Low at gas exchange surface (alveoli in lungs), High at respiring tissues (contracting muscles)
    • Affinity of Hb for oxygen
      High at gas exchange surface, Low at respiring tissues
    • Positive cooperativity

      It is hard for the first oxygen to bind to a haem group as the four polypeptide chains are closely linked. The binding of the first oxygen changes the quaternary structure of the haemoglobin molecule, uncovering the other binding sites on the haem groups and making it easier for the next two oxygen molecules to bind. When the majority of haem groups have already bound to oxygen, it is harder for the last one to find an empty site – so in practice it is harder for the final oxygen to bind.
    • Oxygen dissociation curve and positive cooperativity

      At low partial pressures of oxygen there is little increase in saturation even as oxygen concentration increases, There is then a rapid rise in saturation as more binding sites on haem groups are uncovered, Saturation plateaus even as the partial pressure of oxygen continues to increase – harder for the last oxygen molecules to find empty binding sites
    • Myoglobin

      Found in muscle tissue and has a higher affinity for oxygen at lower partial pressures than normal adult haemoglobin
    • Fetal Haemoglobin

      Has a higher affinity for oxygen at lower partial pressures than adult Hb
    • Lugworm Haemoglobin
      Has a higher affinity for oxygen at lower partial pressures than human Hb
    • Oxygen dissociation curve and haemoglobins with higher affinity for oxygen
      Shifted to the LEFT of adult Hb
    • Bohr shift
      Explains the effect of carbon dioxide concentration on Hb and its affinity for oxygen. An increase in carbon dioxide concentration will decrease the pH of the plasma and affect the tertiary structure of the haemoglobin polypeptide chains, decreasing its affinity for oxygen.
    • At the gas exchange surface
      Carbon dioxide is constantly removed, slightly increasing the pH of the plasma, changing the tertiary shape of the haemoglobin polypeptides into one that more readily associates with oxygen, Hb has a higher affinity for oxygen and more readily binds it
    • At the respiring tissues

      Carbon dioxide is constantly produced and dissolves in the plasma, slightly decreasing the pH of the plasma as carbonic acid is formed, changing the tertiary shape of the haemoglobin polypeptides into one that more readily dissociates from oxygen, Hb has a lower affinity for oxygen and more readily unloads it
    • Oxygen dissociation curve and effect of carbon dioxide
      Shifted to the RIGHT of adult Hb
    • Pulmonary circulation

      Transports blood between the heart and the lungs - then back to the heart
    • Systemic circulation
      Transports blood between the heart and the organs and tissues of the body - then back to the heart again
    • Vena Cava
      Delivers deoxygenated blood to the right atrium
    • Pulmonary artery

      Pumps deoxygenated blood out of the right ventricle to the lungs
    • Pulmonary vein
      Delivers oxygenated blood from the lungs to the left atrium
    • Aorta
      Pumps oxygenated blood out of the left ventricle to the organs of the body
    • Diastole
      Atria fill = pressure in atria increases, when pressure is higher in the atria than ventricles – atrioventricular valves open, Ventricle walls relaxed = lowers pressure so semi-lunar valves shut
    • Atrial systole
      Atria contract = forces remaining blood into ventricles, Ventricle walls remain relaxed
    • Ventricular systole
      Pressure in ventricles rises = atrioventricular valves are forced shut, Pressure exceeds aorta and pulmonary artery – blood forced into vessels as semilunar valves open
    • Atrioventricular valves
      Separate atrium and ventricles (bicuspid on left side; tricuspid on right)
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