3.3.4.1 Mass Transport In Animals - Hb

Question 1

Structure of Hb and its relationship with oxygen

Answer 1

• RBC contain Hb
• large protien with quaternary structure - made of 4 polypeptide chains
• each chain has a haem group, contains an iron ion, gives Hb red colour
• Hb has high affinity for o2 - each molecule can carry 4 o2 molecules

Question 2

What occurs to Hb in the lungs

Answer 2

• oxygen joins to haemoglobin in RBC’s to form oxyhaemoglobin
• reversible reaction - o2 leaves oxyhaemoglobin near the body cells, it turns back to Hb.

Question 3

What is oxygen and carbon dioxide partial pressure

Answer 3

• partial p of o2 is a measure of o2 concentration
• the greater the conc of dissolved o2 in cells, the higher the partial pressure
• partial p of co2 is a measure of the conc of co2 in a cell

Question 4

Relationship between Hb and partial pressure

Answer 4

• Hb affinity for o2 varies depending on the partial pressure of o2
• o2 loads into Hb to form oxyhaemoglobin where there is a high partial p
• oxyhaemoglobin unloads o2 where there’s a low partial p

Question 5

Hb in the alveoli, lungs and respiring tissue

Answer 5

• o2 enters the blood capillaries at the alveoli in the lungs. Alveoli have a high partial p so o2 loads onto the Hb to form oxyhaemoglobin.
• when cells respire, they use up o2, lowers the partial p of o2. RBC deliver oxyhaemoglobin to respiring tissues, where it unloads its o2
• the Hb then returns to the lungs to pick up more o2.

Question 6

Describe the oxygen dissociation curve

Answer 6

• where the partial p is high (lungs) Hb has high affinity for o2, so a high saturation of o2
• where there’s partial p is low (respiring tissue) Hb has a low affinity for o2, releases o2 rather than combines with it, low saturation of oxygen

Question 7

Why is the graph an s shape

Answer 7

• Hb combines with the first o2 molecule, the shape alters in a way that makes it easier for other molecules to join.
• Hb starts to become saturated, it gets harder for more o2 molecules to join
• so the curve has a steep bit in the middle where it is easier for the o2 molecules to join, and shallow bits at each end where it’s harder.
• when the curve is steep, small change in partial p of o2 causes a big change in the amount of o2 carried by the Hb

Question 8

How does the co2 conc affect oxygen unloading

Answer 8

• Hb gives up o2 more readily at higher partial p of co2
• when cells respire they produce co2, which raises the partial pressure of co2
• increases the rate of o2 unloading, so the dissociation curve shifts to the right. Saturation of blood with o2 is lower for a given o2 partial p, so more o2 is being released
• called the Bohr shift

Question 9

How is Hb different in different organisms

Answer 9

Organisms that live in environments with a low conc of o2, have Hb with a higher affinity for o2 than human Hb - the dissociation curve is to the left of ours
Organisms that are very active and have a high oxygen demand, have Hb with a lower affinity for o2 than human Hb - the curve is to the right of the human one