8.4

Question 1

how are erythrocytes specialised to carry oxygen?

Answer 1

they have a biconcave disk shape which gives a larger surface area for diffusion

no nucleus or organelles to maximise haemoglobin storage

Question 2

haemoglobin + oxygen

Answer 2

oxyhaemoglobin

Question 3

what is positive cooperativity?

Answer 3

when oxygen binds to one haem group, the shape of haemoglobin changes to make it easier for another oxygen to bind

Question 4

why do oxygen dissociation curves have an s shape?

Answer 4

because of positive cooperativity making it easier to gain or lose oxygen when one has binded to a haem group

Question 5

what affinity does haemoglobin have for oxygen at high p(O2)?

Answer 5

high affinity

Question 6

what affinity does haemoglobin have for oxygen at low p(O2)?

Answer 6

low affinity

Question 7

what is the Bohr effect?

Answer 7

at high p(CO2), haemoglobin gives up oxygen more easily

Question 8

why is the Bohr effect important when exercising?

Answer 8

at high p(CO2) in respiring cells, O2 can be released and used in aerobic respiration to provide ATP

CO2 can be removed by haemoglobin which prevents toxic build up

Question 9

what affinity does haemoglobin have for oxygen at high p(CO2)?

Answer 9

low affinity

Question 10

what affinity does haemoglobin have for oxygen at low p(CO2)?

Answer 10

high affinity

Question 11

what is the change in the graph for Bohr effect?

Answer 11

shifts to the right

Question 12

what is different about fetal haemoglobin?

Answer 12

fetal haemoglobin has a higher affinity for oxygen

this allows for oxygen to be transferred to the placenta from the maternal blood more easily

Question 13

what is the change in the graph for fetal haemoglobin?

Answer 13

shifts to the left left

Question 14

what happens to CO2 when it enters the erythrocyte?

Answer 14

it reacts with water to form carbonic acid (H2CO3)

Question 15

which enzyme catalyses the production of carbonic acid?

Answer 15

carbonic anhydrase

Question 16

what does carbonic acid dissociate into?

Answer 16

HCO3- ions
H+ ions

Question 17

what do the HCO3- ions do?

Answer 17

they diffuse out of the erythrocyte down the concentration gradient

Question 18

what is caused by HCO3- ions diffusing out?

Answer 18

a change in the electrochemical gradient as it becomes more positive

Question 19

what restores the electrochemical gradient?

Answer 19

Cl- ions move into the erythrocyte

Question 20

what is the movement of Cl- into the erythrocyte called?

Answer 20

chloride shift

Question 21

how does a high p(CO2) cause oxygen to be released by haemoglobin?

Answer 21

oxygen stored as oxyhaemoglobin

CO2 reacts with water to form carbonic acid

carbonic acid dissociates into HCO3- and H+

H+ ions causes oxyhaemoglobin to release oxygen and react to form haemoglobonic acid

Question 22

how do erythrocytes maintain a steep concentration gradient to take in more CO2?

Answer 22

by converting CO2 into carbonic acid, it reduces the CO2 concentration inside the erythrocyte while the respiring tissues will have a high CO2 concentration from respiration

CO2 moves into erythrocyte down the conc gradient

Question 23

when does carbonic anhydrase catalyse the reverse reaction?

Answer 23

when there is a low concentration of CO2 like in the lungs

Question 24

how does CO2 leave the erythrocyte?

Answer 24

carbonic acid is broken down into CO2 and water which increases the CO2 concentration gradient in the erythrocyte

CO2 then moves down the concentration gradient, out of the erythrocyte and into the lungs

Question 25

how does haemoglobin act as a buffer?

Answer 25

when acid is added it accepts H+ ions to form haemoglobonic acid which raises the pH back to normal

Question 26

how does CO2 reduce Hb’s affinity for O2?

Answer 26

reacts with water to form carbonic acid
carbonic acid dissociates into H+ ions
H+ ions react with Hb to form haemoglobonic acid which prevents oxygen binding