7 - Mass Transport

• What is the structure of haemoglobin?

  Haemoglobin is a protein with a quaternary structure. It has four haem groups, containing iron.
• What is the oxygen dissociation curve?

  Oxygen is loaded in regions with high partial pressure of oxygen (e.g. alveoli) and is unloaded in regions of low partial pressure of oxygen (e.g. respiring tissues).

  
• What is co-operative binding?

  The affinity haemoglobin has for oxygen changes depending on how many oxygen molecules are already associated with it. Haemoglobin can associate with four oxygen molecules and as each molecule binds, the shape of haemoglobin changes making the binding of further oxygen molecules easier. Therefore, in areas with high partial pressure of oxygen, meaning a high concentration, the affinity of haemoglobin for oxygen is high and it loads more oxygen. In humans, the alveoli have a high partial pressure of oxygen meaning haemoglobin will readily load with oxygen here
• What is the Bohr effect?

  The Bohr effect is when a high carbon dioxide concentration causes the oxyhaemoglobin curve to shift to the right. The affinity for oxygen decreases because the acidic carbon dioxide changes the shape of haemoglobin slightly. When carbon dioxide dissolves in liquid, carbonic acid forms and this decrease in pH changes the shape of haemoglobin slightly, which is why the affinity for oxygen decreases. In respiring tissues, this is advantageous, as the haemoglobin delivers the oxygen to the site of respiring cells so that aerobic respiration can continue.
• How are animals adapted for mass transport?

  Many animals are adapted to their environment by possessing different types of haemoglobin with different oxygen transport properties. Animals like lugworms, whales and even human foetuses have myoglobin. Myoglobin has a very high affinity for oxygen, even at very low partial pressures. Therefore, it acts as an oxygen store, holding onto oxygen and not dissociating until nearly all oxygen has been used up in cells.
• How is llama haemoglobin adapted to the llama's environment?

  Llamas live at high altitudes where the atmospheric pressure is low and so there is a lower partial pressure of oxygen. Llamas have a type of haemoglobin with a higher affinity of oxygen so that despite the low partial pressure of oxygen, it is still loaded onto haemoglobin. The curve shifted to the left, indicating a higher affinity even at low pp Oxygen
• How is dove haemoglobin adapted to the dove's environment?

  Animals with faster metabolisms, like a fast-moving dove, need more oxygen for respiration to provide energy for contracting muscles.

  
  

  Therefore their haemoglobin has a lower affinity so that it can readily unload oxygen, which is why the curve has shifted to the right

  
• What is the circulatory system of a mammal?

  Double circulatory system

  
  

  Closed - the blood remains within the blood vessels

  
  

  Double - the blood passes through the heart twice in each circuit. There is one circuit that delivers blood to the lungs and another circuit that delivers blood to the rest of the body.
• Why do mammals need a double circulatory system?

  To manage the pressure of blood flow. The blood flows through the lungs at a lower pressure. This prevents damage to the capillaries in the alveoli and also reduces the speed at which the blood flows, enabling more time for gas exchange. The oxygenated blood from the lungs then goes back through the heart to be pumped out at a higher pressure to the rest of the body. This is important to ensure that the blood reaches all the respiring cells in the body
• What are the major blood vessel attached to the following organs?

  • Heart (vena cava, aorta, pulmonary artery and pulmonary vein)
  • Lungs (pulmonary artery and pulmonary vein)
  • Kidneys (renal artery and renal vein)
• Tissue fluid is the liquid that surrounds cells. What does it contain?

  1. water
  2. glucose
  3. amino acids
  4. fatty acids
  5. ions
  6. oxygen
• Arteries:~

  • Muscle layer = thicker than veins so constriction & dilation can occur to control volume of blood
  • Elastic layer = thicker than veins to help maintain blood pressure. Walls can stretch and recoil in response to heart beat
  • Wall thickness = thicker than veins to help prevent the vessels bursting due to high pressure
  • No valves
• Arterioles:~

  • Muscle layer = thicker than arteries to restrict blood flow into capillaries
  • Elastic layer = thinner than in arteries as pressure is lower
  • Wall thickness = thinner as pressure is slightly lower
  • No valves
• Veins:~

  • Muscle layer = relatively thin so it can't control blood flow
  • Elastic layer = relatively thin as pressure is lower
  • Wall thickness = thin as pressure is lower so low risk of bursting. Thinness means vessels are easily flattened, which helps the flow of blood up to the heart
  • Yes valves
• Capillaries:~

  • Muscle layer = N/A
  • Elastic layer = N/A
  • Wall thickness = One cell thick consisting of only lining layer, providing a short diffusion distance for exchanging materials between blood & cells
  • No valves
• How is tissue fluid formed?

  1. Capillaries have small gaps in the walls so that liquid and small molecules can be forced out.
  2. As blood enters the capillaries from arterioles, the smaller diameter results in a high hydrostatic pressure so water, glucose, amino acids, fatty acids, ions and oxygen are forced out.
  3. This is known as ultrafiltration.
  4. Red blood cells, large proteins and platelets are too big to fit through the tiny gaps, so they remain within the capillary.

  
• How is the liquid reabsorbed?

  • Large molecules remain in the capillaries and therefore create a lowered water potential. Towards the venule end of the capillaries, the hydrostatic pressure is lowered due to the loss of liquid, but the water potential is very low due to the proteins that remained within the capillary. Therefore, water re-enters the capillaries by osmosis at the venule end.

  
• Not all the liquid will be reabsorbed by osmosis, as equilibrium will be reached. How is the rest of the liquid reabsorbed?

  The rest of the liquid is absorbed into the lymphatic system and eventually drains back into the bloodstream near the heart. This liquid that is transferred in the lymphatic system is called lymph.
• What unique properties does cardiac muscle have?

  • It is myogenic, meaning it can contract and relax without nervous or hormonal stimulation
  • It never fatigues, as long as it has a supply of oxygen
• What is the location & function of the coronary arteries?

  These are the blood vessels that supply the cardiac muscle with oxygenated blood. They branch off from the aorta.
• Which ventricular wall is thickest and why?

  The left ventricle has a much thicker muscular wall in comparison to the right ventricle to enable larger contractions of the muscle to create a higher pressure to pump blood around the body.
• What are the four major blood vessels attached to the heart and describe their role?

  • Vena Cava - carries deoxygenated blood from the body into the right atrium.
  • Pulmonary Vein -carries oxygenated blood from the lungs to the left atrium.
  • Pulmonary Artery - carries deoxygenated blood from the right ventricle to the lungs to become oxygenated.
  • Aorta - carries oxygenated blood from the left ventricle to the rest of the body

  
• What are the valves in the heart named & describe their location?

  1. Semilunar valve - located in the aorta & pulmonary artery
  2. Atrioventricular valve - located between atria and ventricles

  
• What causes a valve to?

  Open - Valves open if pressure is higher behind them, compared to in front

  
  

  Closed - If pressure is higher in front, valve remains closed
• Cardiac output = heart rate X stroke volume
• What is stroke volume?

  The volume of blood that leaves the heart each beat in dm3
• Describe the three stages of the cardiac cycle - Diastole?

  The atria and ventricular muscles are relaxed. This is when blood will enter the atria via the vena cava and pulmonary vein. The blood flowing into the atria increases the pressure within the atria
• Describe the three stages of the cardiac cycle - Atrial systole?

  The atria muscular walls contract, increasing the pressure further. This causes the atrioventricular valves to open and blood to flow into the ventricles. The ventricular muscular walls are relaxed (ventricular diastole)
• Describe the three stages of the cardiac cycle - Ventricular systole?

  After a short delay, the ventricle muscular walls contract, increasing the pressure beyond that of the atria. This causes the atrioventricular valves to close and the semilunar valves to open. The blood is pushed out of the ventricles into the arteries (pulmonary and aorta)
• What is transpiration?

  Transpiration is the loss of water vapour from the stomata by evaporation.
• Describe how four different factors affect the rate of transpiration: 1 Light intensity?

  There is a positive correlation between light intensity and transpiration. This is because the higher the light intensity, the more stomata that open and this provides a larger surface area for evaporation
• Describe how four different factors affect the rate of transpiration: 2 Temperature?

  There is a positive correlation between temperature and transpiration. The more heat there is the more kinetic energy, and therefore faster-moving molecules. This increases evaporation
• Describe how four different factors affect the rate of transpiration: 3 Humidity?

  There is a negative correlation between humidity and transpiration. The more water vapour in the air, the more positive the water potential is outside of the leaf. This reduces the water potential gradient and therefore reduces evaporation.
• Describe how four different factors affect the rate of transpiration: 4 Wind?

  There is a positive correlation between wind (air movement) and transpiration. The windier it is, the more humid air containing the water vapour that is blown away. This maintains the water potential gradient, increasing evaporation.
• How does water move up the xylem?

  1. Water vapour evaporates out of stomata on leaves. This loss in water volume creates a lower pressure.
  2. When this water is lost by transpiration more water is pulled up the xylem to replace it (moves due to negative pressure).
  3. Due to the hydrogen bonds between water molecules, they are cohesive (stuck together). This creates a column of water within the xylem.
  4. Water molecules also stick to the walls of the xylem, helping to pull the water column upwards.
  5. As water is pulled up the column, the xylem it creates tension, pulling the xylem in to become narrower.
• What is the function of the phloem?

  Phloem is the tube responsible for the transport of organic substances in plants, such as sugars.
• Describe the structure of: Sieve tube elements?

  These are living cells, but they contain no nucleus and very few organelles. This is to make the cell more hollow and therefore provide less resistance to the flow of sugars.
• Describe the structure of: Companion cells?

  As the sieve tube elements have few organelles, they depend on the companion cell for resources. The companion cells provide ATP required for active transport of organic substances
• Organic substances, such as sucrose, move in solution from the leaves where they are created in photosynthesis, to respiring cells. The site of production is called the 'source' and the site of use is called the 'sink' in the mass flow hypothesis.
• What is the source of sink mass flow hypothesis?

  • Sucrose lowers the water potential of the source cell. This causes water to enter by osmosis. This increases the hydrostatic pressure in the source cell.
  • The respiring cell is using up sucrose, and therefore it has a more positive water potential. Therefore water leaves the sink cell by osmosis. This decreases the hydrostatic pressure in the sink cell.
  • This results in the source cell having a higher hydrostatic pressure than the sink cell, so the solution is forced towards the sink cell via the phloem.