Transport in Animals - Erythrocytes and Haemoglobin

Question 1

what are the adaptations of erythrocytes

Answer 1

• very small
• biconcave disc
• no nucleus, mitochondria or ER

Question 2

how does being very small help erythrocytes

Answer 2

• short diffusion distance
• squeeze through capillaries so in close contact with tissues

Question 3

how does a biconcave disc help erythrocytes

Answer 3

larger surface area to volume ratio

Question 4

how does no nucleus, mitochondria or ER help erythrocytes

Answer 4

leaves more space for haemoglobin - combines reversibly with oxygen to form oxyhaemoglobin

Question 5

which of the following functions can be carried out in a mature red blood cell:
- protein synthesis
- cell division
- lipid synthesis
- respiration

Answer 5

respiration - anaerobic respiration can occur in the cytoplasm

Question 6

what is haemoglobin

Answer 6

• a globular protein molecule made of four polypeptide chains
• each polypeptide has a haem prosthetic group containing a single iron ion (Fe2+)

Question 7

describe the haem group

Answer 7

has an affinity for oxygen - the iron ion can attract and hold one oxygen molecule

Question 8

describe the formation of oxyhaemoglobin

Answer 8

• formed in the lungs
• reversible reaction

Question 9

where is the oxygen released

Answer 9

in body tissues, this is called dissociation or unloading

Question 10

Describe the process of taking up oxygen

Answer 10

• in the alveoli of the lungs oxygen molecules diffuse into the blood plasma
• oxygen molecules bind to the haemoglobin forming oxyhaemoglobin

Question 11

What maintains a steep concentration gradient in the process of taking up oxygen

Answer 11

• Taking oxygen out of solution maintains a steep concentration gradient
• Therefore more oxygen enters the blood and diffuses into the red blood cells

Question 12

Describe the process of releasing oxygen

Answer 12

• Oxygen molecules are needed in the tissues for aerobic respiration
• Oxyhaemoglobin dissociates releasing the oxygen

Question 13

What does haemoglobins affinity for oxygen depend on

Answer 13

The partial pressure of oxygen (pO2)

Question 14

What is partial pressure of oxygen

Answer 14

A measure of oxygen concentration

Question 15

What is the relationship between haemoglobins affinity for oxygen and pO2

Answer 15

As pO2 increases, so does Hb’s affinity for oxygen

Question 16

What happens when there’s a high pO2

Answer 16

Oxygen loads onto Hb to form oxyhaemoglobin

Question 17

What happens when there’s a lower pO2

Answer 17

Oxyhaemoglobin unloads its oxygen

Question 18

describe loading at alveoli in the lungs

Answer 18

• high pO2 (12-14kPa)
• Hb has a high affinity for O2
• oxygen loads
• Hb 96-97% saturated

Question 19

describe unloading at respiring tissue

Answer 19

• low pO2 (2-5kPa)
• Hb has a low affinity for O2
• oxygen unloads/dissociates
• Hb 20-70% saturated

Question 20

what does a haemoglobin dissociation curve show

Answer 20

the affinity of haemoglobin for oxygen at different partial pressures of oxygen

Question 21

what is the shape of a haemoglobin dissociation curve

Answer 21

s-shaped (sigmoid)

Question 22

why is the first part of the curve not very steep

Answer 22

the first O2 molecule combines relatively slowly with the first haem group.

Question 23

what happens after the first binding

Answer 23

the binding of oxygen with the first haem group causes the shape of the whole haemoglobin molecule to change

Question 24

why does the curve become steeper

Answer 24

as a result of its altered shape, it is much easier for the second and third O2 molecules to bind to their haem groups

Question 25

why does the curve flatten off

Answer 25

it then becomes much harder for the fourth (ie last) oxygen molecule to combine with the fourth haem group

Question 26

do the same shape changes occur during dissociation

Answer 26

yes