Mass transport

• Describe structure of haemoglobin

  -globular protein with quaternary structure

  -4 polypeptide chains - 2 alpha sub-unit and 2 beta sub-unit

  -Each sub-unit contains 1 polypeptide chain and a haem group which contains a single iron ion (Fe2+)

  -This FE2+ has a high affinity for oxygen

  -4 Oxygen molecules can bind to four haem groups

  -oxyhaemoglobin= 100% saturated
• Oxygen Loading


  Oxygen binds to Hb in the alveoli, replacing CO2. Affinity is high, and Hb is saturated.
• Bohr Shift

  The Bohr shift increases the affinity of Hb for CO2, facilitating CO2 removal in the lungs.
• Unloading Oxygen

  Oxygen is released from Hb in the tissues due to low pO2. Affinity is low, and Hb becomes unsaturated.
• Explain how oxygen is loaded, transported and unloaded in blood

  -Haemoglobin has high affinity for oxygen at high partial pressure

  -Oxygen binds/loads to haemoglobin in lungs

  -and unloads in respiring cells/tissues at low partial pressure of oxygen

  -Unloading linked to higher carbon dioxide concentration; Bohr Shift;
• Explain the shape of the haemoglobin saturation and dissociation curve

  
  

  • the graph is a sigmoid or s-shaped
  • this is because binding of first oxygen molecule causes the haemoglobin's quaternary structure to change shape
  • this uncovers the other O2 binding sites thus making it easier for other oxygen molecules to bind this is know as positive cooperativity
  • Once 3 o2 molecules are bound the graph becomes shallower this is because its harder for the final oxygen to bind as there is only one binding site available
• Describe the Bohr effect

  -Haemoglobin's affinity for oxygen also changes at different concentrations of carbon dioxide. At higher partial pressures of carbon dioxide haemoglobin has a lower affinity for oxygen causing oxyhaemoglobin to dissociate more readily

  -This is useful because tissues with high rate of respiration will be producing large amounts of carbon dioxide. This ensures that oxygen is unloaded from haemoglobin at respiring tissues.

  -high co2 concentration shifts the dissociation curve to the right
• Name 3 common features of a mammalian system

  -suitable medium for transport, water based to allow substances to dissolve and because it can be moved around easily

  -means of moving the medium and maintaining pressure throughout the body

  -means of controlling flow so it maintains unidirectionality such as valves
• How does increasing co2 levels affect haemoglobin ?

  -The production of Co2 causes the formation of carbonic acid which causes a fall in pH

  -The fall in pH causes a change in the structure of haemoglobin causing it to release its oxygen more readily

  -Thus the more Co2 being produced the more O2 being released for respiration
• Outline a feature of the heart

  -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
• Outline the structure of the chambers and how its related to their function

  Atria :

  • thinner muscular wall - as its is only pumping blood to ventricles so doesn't need to contract as hard
  • elastic wall to stretch when blood enters Ventricles :
  • thick muscular walls - to enable bigger contraction this created a higher blood pressure to enable blood to flow longer distances
• Give 2 ways by which directional flow is maintained in the circulation system

  -pressure gradient

  -valves to stop backflow
• Describe atrial systole

  -wall of atria contact as a result atrial volume decreases and atrial pressure increases

  -pressure in atria rises above that in ventricles forcing AV valves to open

  blood is forced into ventricles
• Describe ventricular systole

  -walls of ventricles contract as a result the volume decreases and pressure increases above that of the atria

  -Forces AV valve to close pressure in ventricular rises above that of aorta and pulmonary artery

  -This forces the semi lunar valves to open so blood is forced ito the arteries and out
• Describe cardiac diastole

  -atria and ventricles are relaxed

  -blood enters the atria increasing the pressure behind the AV valve causing them to open

  -Blood then enters the ventricles from the atria and the semi-lunar valves remain closed
• Give four structural features of the aorta and explain how they relate to its function

  -elastic tissue to allow stretching - smooths outflow of blood

  -thick wall withstands pressure

  -smooth endothelium reduces friction

  -semi-lunar valve prevents backflow
• Suggest why there are larger fluctuations in blood pressure in the aorta than in the small arteries

  -aorta is closer to the heart

  -aorta has elastic tissue

  -aorta can stretch/recoil
• How is the structure of veins related to their function ?

  -thin muscle walls

  -has valves to prevent backflow

  -thin layer of elastic fibre as BP is low

  -movement of blood due to contraction of skeletal muscle
• How is the structure of arteries related to their function

  -Thick muscular wall and lots of elastic tissue to withstand high BP

  -folded endothelium which enables expansion under high BP

  -small lumen ensure high BP is maintained
• How is structure of arterioles related to their function?

  -Thicker muscular layer - to contact so it can constrict its lumen to control amount of blood flow to capillaries/tissues

  • thinner elastic layer- blood is at lower BP
• How is the structure of capillaries related to their function?

  -walls are only one cell thick so shorter diffusion pathway

  -very narrow so can permeate tissues and red blood cells can lie flat against the wall effectively delivering O2 to tissues

  -numerous and highly branched providing a larger surface area
• Describe the mass flow hypothesis for the mechanism of translocation

  • In source / leaf sugars actively transported into phloem
  • By companion cells;
  • Lowers water potential of sieve cell / tube and water enters by osmosis;
  • Increase in pressure causes mass movement (towards sink / root);-
  • Sugars used / converted in root for respiration for storage;
• What are the four key conditions that affect the rate of transpiration?


  • Light intensity
  • Temperature
  • Humidity
  • Wind
• How does light intensity affect the rate of transpiration?


  Higher light intensity causes more stomata to open, increasing evaporation
• What is the effect of temperature on the rate of transpiration?


  Higher temperature increases the kinetic energy of water molecules, increasing evaporation
• How does humidity affect the rate of transpiration?


  Higher humidity decreases the rate of transpiration due to a reduced water potential gradient
• What is the relationship between wind and the rate of transpiration?


  More wind increases the rate of transpiration by carrying away water vapor
• What does the cohesion tension theory explain?


  How water can move up a plant against gravity
• What is cohesion in the context of water molecules?


  The sticking together of water molecules due to hydrogen bonds
• How does cohesion affect water movement in the xylem?


  It allows water to travel up the xylem as one continuous column
• What is adhesion in the context of water movement?


  The sticking of water molecules to the walls of the xylem
• How does capillarity relate to the movement of water in plants?


  Narrow xylem increases capillarity, helping water move up
• What is root pressure?


  The pressure created when water moves into the roots by osmosis
• How does root pressure contribute to water movement in plants?


  It pushes water upwards due to increased pressure in the roots
• What are the three main components of the cohesion tension theory?

  • Cohesion: Sticking together of water molecules
  • Adhesion: Water molecules sticking to xylem walls
  • Root pressure: Positive pressure pushing water upwards
• How does transpiration create a pull on the water column in plants?


  Evaporation of water creates a lower pressure, pulling water up from the xylem
• What role do hydrogen bonds play in the cohesion tension theory?


  They allow water molecules to stick together, forming a continuous column
• How does tension affect the diameter of the xylem?


  Tension pulls the xylem walls in, making the diameter narrower
• What is the overall process of water movement in plants according to the cohesion tension theory?


  1. Water evaporates from stomata (transpiration)
  2. Lower pressure created in the leaf
  3. Water from xylem moves up to replace lost water
  4. Cohesion keeps water molecules together
  5. Adhesion helps water stick to xylem walls
  6. Tension pulls water column upwards
• What is the final summary of transpiration and the cohesion tension theory?


  Transpiration is the loss of water vapor, and the cohesion tension theory explains how water moves up a plant against gravity