transport of Co2 and O2

Question 1

what is haemoglobin

Answer 1

red, oxygen carrying pigment found in RBC

Question 2

describe properties of haemoglobin

Answer 2

• globular conjugated protein made of 4 peptide chains
• contains 4 Fe haem prosthetic groups

Question 3

what is meant by ‘haemoglobin has a high affinity for oxygen’?

Answer 3

increased tendency to combine with oxygen (1 haemoglobin can carry 4 O2 molecules)

Question 4

what is the reversible reaction that forms oxyhaemoglobin

Answer 4

Hb + 4O2 = Hb(O2)4 (haemoglobin + 4 oxygen = oxyhaemoglobin)

Question 5

how is a steep concentration gradient formed between RBC and air in alveoli

Answer 5

when erythrocytes enter lung capillaries, the oxygen levels in cells are relatively low

Question 6

explain how oxygen binds to haemoglobin

Answer 6

1. oxygen moves into the erythrocyte and binds to haemoglobin
2. when one oxygen molecule binds to a haem group, the molecule changes shape, making it easier for the next oxygen molecule to bind

Question 7

why is oxygen binding to haemoglobin known as positive cooperation

Answer 7

oxygen binding to a haem group increases haemoglobin’s affinity for oxygen, maintaining a steep concentration gradient until all haemoglobin is saturated

Question 8

what happens when blood reaches body tissues

Answer 8

• concentration of oxygen in cytoplasm of body cells is lower than erythrocytes so oxygen moves out down a CG
• once the first oxygen is released, the molecule changes shape again so remaining oxygen is released more easily

Question 9

what is an oxygen dissociation curve?

Answer 9

a graph showing the affinity of haemoglobin for oxygen

Question 10

what do oxygen dissociation curves help us to understand?

Answer 10

how the blood carries and release oxygen

Question 11

what is partial pressure of oxygen (PO2)

Answer 11

a measure of oxygen concentration

Question 12

when is partial pressure of oxygen at its highest and why?

Answer 12

in the lungs as haemoglobin is rapidly loaded with oxygen

Question 13

when is partial pressure of oxygen at its lowest and why?

Answer 13

in respiring tissues as oxygen is released rapidly from haemoglobin

Question 14

what % of oxygen is released into body cells when inactive and what happens to the rest?

Answer 14

25% - rest acts as reservoir for when demand suddenly increases

Question 15

what happens when partial pressure of Co2 increases?

Answer 15

haemoglobin releases oxygen more easily

Question 16

how is the bohr effect represented graphically?

Answer 16

as the proportion of Co2 increases, the oxygen dissociation curve shifts to the right

Question 17

how is fetal haemoglobin represented graphically?

Answer 17

the oxygen dissociation curve shifts to the left

Question 18

compare the affinity for oxygen in adults with fetuses

Answer 18

fetal haemoglobin has a higher affinity for oxygen than the mother at the same partial pressure of oxygen

Question 19

why is it important that fetal haemoglobin has a higher affinity for oxygen?

Answer 19

• the fetus gets oxygen from its mothers blood - one the blood has reached the placenta, its oxygen saturation has decreased
• higher affinity = it absorbs more oxygen

Question 20

what 3 ways is Co2 transported to the lungs?

Answer 20

• 5% is dissolved in plasma
• 10-20% is combined with amine groups in polypeptide chains of haemoglobin (forms carbaminohaemoglobin)
• 75-85% is converted into hydrogen carbonate ions (HCO3-) in red blood cell cytoplasm

Question 21

explain how CO2 is transported to the alveoli for expiration

Answer 21

1. CO2 reacts with water to form carbonic acid (H2CO3-) catalysed by carbonic anhydrase
2. carbonic acid dissociates into H+ ions and HCO3- ions
3. H+ ion increase causes oxyhaemoglobin to unload oxygen so haemoglobin can take up H+ ions forming haemoglobinic acid (stopping H+ ions increasing cell acidity)
4. HCO3- ions diffuse out of the RBC and are transported in blood plasma
5. Cl- ions compensate for loss of HCO3- by diffusing into the RBC - known as chloride shift
6. when blood reaches lungs, low PCo2 causes some HCO3- and H+ ions to recombine into CO2 and water
7. CO2 then diffuses into alveoli and is breathed out