Gaseous Exchange

Master Gaseous Exchange: Haemoglobin, O2/CO2 transport, and plant stomata.

1. Describe the structures and functions of haemoglobin. Structure:A conjugated protein with a quaternary structureConsists of 4 polypeptide chains2 alpha chains and 2 beta chainsEach of these polypeptide chains is associated with a haem groupwith an iron(II) ion at its centerEach iron ion can bond with one oxygen moleculeFunctions:Major function is to transport oxygen from the lungs to the tissuesOne haemoglobin molecule can bond with 4 oxygen moleculeforming oxyhaemoglobinHaemoglobin has a high affinity for oxygenWhen one of the iron atom binds with an O2 moleculeThe Hb structure will be alteredThe remaining 3 ion atoms will accept the O2 readily 2. With the aid of labeled diagram, describe oxygen dissociation curve for haemoglobin. Hb has a high affinity towards O2The higher the partial pressure of oxygen (ρO2), the higher is its percentage of saturation with O2At higher partial pressure of oxygen, more haem groups binds to oxygen cooperative bindingAt very higher partial pressure of oxygen, hemoglobin is very saturated with O2.All hemoglobin bind with O2At low partial pressure of O2, it easily dissociates from hemoglobin . Less hemoglobin binds with O2 Explain the regulation of stomatal opening and closing based on starch-sugar hypothesis. Opening of stomaDuring photosynthesis, glucose is actively produced in guard cells.Decreases the water potential of the cell sap of guard cells.The water potential of guard cells is lower than surrounding epidermal cells.Water enters the guard cells by osmosis.Guard cells become turgid.Stomata open.Closing of stomaCO2 is released during respiration (not used in photosynthesis).This will increase the concentration of H+ (pH will decrease).Sugar converts into starch in the guard cells.Water potential in the guard cell increase.Water leaves the guard cells into neighbouring cells by osmosis.Guard cells become flaccid.Stomata close 3. Describe the transport of carbon dioxide from tissues to the lungs in human. There are 3 ways of which the CO2 is transported in the blood:7% of the CO2 is transported in solution in blood plasma23% binds to the amino ends of the haemoglobin forming carbaminohaemoglobin70% is transported in the blood in the form of bicarbonate ions where,The CO2 will diffuse out of the tissue into the blood plasmaThe CO2 will then diffuse into the red blood cellThis reaction is catalyzed by the enzyme carbonic anhydrase found in the red blood cellThe carbonic acid will dissociates into hydrogen ions (H+) and bicarbonate ionsThe hydrogen ions (H+) will bind to haemoglobin to form haemoglobinic acidThe bicarbonate ions then diffuse out of the RBC into the blood plasma and transported into the lungs.To maintain electrochemical balance, a chloride ion (Cl-) enters the erythrocyte for each HCO3- that exits. This called chloride shift.Erythrocytes move along blood vessel to lung.In the lungs,The bicarbonate ions diffuses from the plasma into red blood cellsIt will then combine with hydrogen ion to form carbonic acid.The carbonic acid will be converted back into carbon dioxide/ CO2 and waterThe carbon dioxide/ CO2 from carbaminohaemoglobin is also releasedCarbon dioxide/ CO2 will then diffuse into the blood plasma and into alveolar space in the lungs