Mass transport

• describe the structure of haemoglobin

  primary structure- sequence of amino acids in the four polypeptide chains

  secondary structure- in which each of these polypeptide chains is coiled into a helix

  tertiary structure- in which each polypeptide is folded into a precise shape [an important factor in its ability to carry oxygen]

  quaternary structure- in which all four polypeptides are linked together to form an almost spherical molecule. each polypeptide is associated with a haem group which contains a ferrous ion. each ferrous ion can combine with a single oxygen molecule. [a total of four]
• what is the process by which haemoglobin binds with oxygen

  loading or associating
• what is the process by which haemoglobin releases its oxygen

  unloading or dissociating
• haemoglobins with a high affinity for oxygen take up oxygen more easily, but release it less easily. haemoglobins with a low affinity for oxygen take up oxygen less easily but release it more easily
• what is the role of haemoglobin

  transport oxygen
• to be efficient at transporting oxygen what must haemoglobin do?

  • readily associate with oxygen at the surface where gas exchange takes place
  • readily dissociate from oxygen at those tissues requiring it
• haemoglobin changes affinity for oxygen under different conditions. in the presence of carbon dioxide, the new shape of haemoglobin binds more loosely to oxygen, as a result it releases its oxygen
• describe the attachment of the first oxygen molecule

  the shape of the haemoglobin molecule makes it difficult for the first oxygen molecule to bind to one of the sites on its four polypeptide subunits because they are closely united. therefore at low oxygen concentrations, little oxygen binds to haemoglobin. which is why the gradient of the oxygen dissociation curve is shallow initially
• how does the binding of the first oxygen molecule impact loading of the rest

  the binding of the first oxygen molecule changes the quaternary structure of the haemoglobin molecule, causing it to change shape. this change makes it easier for the other subunits to bind to an oxygen molecule. in other words, the binding of the first oxygen molecule induces the other subunits to bind to an oxygen molecule
• what is positive cooperativity

  it takes a smaller increase in the partial pressure of oxygen to bind the second oxygen molecule than it did to bind the first one. this is why the oxygen dissociation curve steepens
• how does the ease of oxygen binding change after the binding of the third oxygen molecule


  it is harder. this is due to probability. with the majority of the binding sites occupied, it is less likely that a single oxygen molecule will find an empty site to bind to. this causes the oxygen dissociation curve to reduce and the graph flattens off
• the further to the left the oxygen dissociation curve, the greater the affinity of haemoglobin for oxygen [loads readily but unloads less easily]
• the further to the right the curve, the lower is the affinity of haemoglobin for oxygen [it loads oxygen less readily but unloads it more easily]
• describe the affinity of haemoglobin at the gas exchange surface

  the concentration of carbon dioxide is low because it diffuses across the exchange surface and is excreted from the organism. the affinity of haemoglobin for oxygen is increased, which, coupledd with the high concentration of oxygen in the lungs, means that oxygen is readily loaded by haemoglobin. the reduced carbon dioxide concentration has shifted the oxygen dissociation curve to the left
• describe the affinity of oxygen in rapidly respiring tissues

  the concentration of carbon dioxide is high. the affinity of haemoglobin for oxygen is reduced, which, coupled with the low concentration of oxygen in the muscles, means that oxygen is readily unloaded from the haemoglobin into the muscle cells. the increased carbon dioxide has shifted the oxygen dissociation curve to the right
• • at the gas - exchange surface carbon dioxide is constantly being removed
  • the PH is slightly raised due to the low concentration of carbon dioxide
  • the higher PH changes the shape of haemoglobin into one that enables it to load oxygen readily
  • this shape also increases the affinity of haemoglobin for oxygen, so it is not released while being transported in the blood
  • in the tissues, carbon dioxide is produced by respiring cells
  • carbon dioxide lowers tissue blood PH
  • lower PH changes haemoglobin shape to lower affinity
  • haemoglobin releases oxygen into respiring tissues
• what is the overall saturation of haemoglobin at atmospheric pressure

  97%
• the blood returning to the lungs will contain haemoglobin that is still ___ saturated with oxygen

  75%
• why do large animals have a transport system?

  because larger animals have a smaller surface area to volume ratio, their needs cannot be met by body surface alone. this means that a specialist exchange surface is required and a transport system is required to take materials from cells to exchange surfaces and vise versa
• what two factors determine if an organism has a specialised transport medium, and whether or not its circulated by a pump

  1. the surface area to volume ratio
  2. how active the organism is

  the lower the surface area to volume ratio, and the more active the organism, the greater is the need for a specialised transport system with a pump
• what are the common features of transport systems

  • a suitable medium in which to carry materials. this is normally a liquid based on water because it readily dissolves substances and can be moved aroundd easily, but may be a gas
  • a form of mass transport in which the transport medium is moved in bulk over long distances
  • a closed system of tubular vessesl that contains the transport medium
  • a mechanism for moving the transport medium. this requires a pressure difference
• how is a pressure difference achieved in transport systems in mammals

  • animals use muscular contraction either of the body muscles or of a specialised pumping organ
  • plants rely on natural, passive processes such as the evapouration of water.
  • both need a mechanism to maintain the mass flow movement in one direction
  • both need a means of controlling the flow of the transport medium to suit the changing needs of different parts of organisms
  • both need a mechanism for the mass flow of water or gases
• what sort os transport system do mammals have

  they have a closed, double circulatory system

  this is where blood is confined to vessels and passes twice through the heart for each complete circuit of the body.

  this is because when blood is passed through the lungs, its pressure is reduced. if it were to pass immediately to the rest of the body its low pressure would make circulation very slow. blood is therefore returned to the heart to boost its pressure before being circulated around the body. this is needed because animals have a high body temperature and metabolism
• what is the heart?

  a muscular organ that lies in the thoracic cavity behind the sternum. it operates continuously and tirelessly throughout the life of an organism
• the left side of the heart deals with oxygenated blood from the lungs, while the right side deals with deoxygenated blood from the body
• what is the atrium?

  thin walled and elastic and stretches as it collects blood
• what are the ventricles

  much thicker muscular wall as it has to contract strongly to pump blood some distance, either to the lungs or to the rest of the body
• what valve lies between the atrium and ventricle on the left side of the heart

  the left atrioventricular [bicupsid] valve
• what valve lies between the atrium and ventricle on the right side of the heart

  the right atrioventricular [tricupsid] valve
• the ventricles pump blood away from the heart and into arteries
• the atria receive blood from the veins
• what are the vessels called that connect the heart to the lungs

  pulmonary vessels
• what is the aorta

  connected to the left ventricle and carries oxygenated blood to all parts of the body except the lungs
• what is the vena cava

  connected to the right atrium and brings deoxygenated blood back from the tissues of the body [except the lungs]
• what is the pulmonary artery

  connected to the right ventricle and carries deoxygenated blood to the lungs, where its oxygen is replenished and its carbon dioxide is removed.
• what is the pulmonary vein

  connected to the left atrium and brings oxygenated blood back from the lungs to the heart
• what blood vessels supply the heart with oxygen


  coronary arteries - which branch off the aorta shortly after is leaving the heart
• what is the result of blocking coronary arteries

  myocardial infarction, or heart attack. this is because an area of the heart muscle is deprived of blood and therefore oxygen. the muscle cells in this region are unable to respire and so die.
• what is the cardiac cycle

  the heart undergoes a sequence of events that is repeated in humans around 70 times each minute when at rest. it involves contraction [systole] and relaxation [diastole]
• explain diastole [relaxation of the heart]

  blood returns to the atria of the heart through the pulmonary vein [from the lungs] and the vena cava [from the body]. as the atria fill, the pressure in them rises. when this pressure exceeds that in the ventricles, the atrioventricular valves open allowing the blood to pass into the ventricles, aided by gravity. the muscular walls of both the atria and ventricles are relaxed at this stage. the relaxation of ventricle walls causes them to recoil and reduced the pressure within the ventricle. this closes semi-lunar valves.