Haemoglobin

Question 1

Describe how haemoglobin normally loads oxygen in the lungs and unloads it in a tissue cell. (6)

Answer 1

• Oxygen combines (reversibly) to produce oxyhaemoglobin;
• each haemoglobin molecule/ one haemoglobin may transport 4 molecules of oxygen;
• high partial pressure of oxygen / oxygen tension / concentration in lungs;
• haemoglobin (almost) 95% / 100% saturated;
• unloads at low pO2 (in tissues);
• presence of carbon dioxide displaces curve further to right / increases oxygen dissociation;
• allows more O2 to be unloaded;
• increase temp/ acidity allows more O2 to be unloaded;
• low pO2 / increase CO2 / increase term / increase acid occur in vicinity of respiring tissue;

Question 2

Explain how oxygen in a red blood cell is made available for respiration in active tissues.

Answer 2

• CO2 (increased) respiration;
• (increased) dissociation oxygen from haemoglobin;
• Low partial pressure in tissues/plasma;
• Oxygen diffuses from red blood cells to tissues;

Question 3

The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus. (3)

Answer 3

• Higher affinity / loads more oxygen;
• At a lower partial pressure/pO2;
• Oxygen moves from mother/to fetus;

Question 4

Explain how oxygen is loaded, transported and unloaded in the blood. (5)

Answer 4

• Haemoglobin carries oxygen / has a high affinity for oxygen / oxyhaemoglobin;
• In red blood cells;
• Loading/uptake/association in lungs at high p.O2;
• Unloads/ dissociates / releases to respiring cells/tissues at low p.O2;
• Unloading linked to higher carbon dioxide (concentration);

Question 5

Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.

Explain why.

Answer 5

1. Binding of first oxygen changes tertiary / quaternary (structure) of haemoglobin; [conformational shift caused]
2. Creates / leads to / uncovers second / another binding site OR Uncovers another iron / Fe / haem group to bind to;

Question 6

Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin.

Answer 6

1. Increases/more oxygen dissociation/unloading OR Decreases haemoglobin’s affinity for O2;
2. (By) decreasing (blood) pH/increasing acidity;

Question 7

What is Affinity?

Answer 7

The “chemical attraction” for O2
- higher affinity = more O2 binds
- lower affinity = less O2 binds

Question 8

What is Saturation? (haemoglobin)

Answer 8

how much oxygen is bound to haemoglobin
- higher saturation = more O2 bound
- lower saturation = less O2 bound

Question 9

What is Association?

Answer 9

Binding of O2 to haemoglobin
- (in blood capillaries around alveoli)

Question 10

What is Dissociation?

Answer 10

Release of O2 from haemoglobin
- (into blood at respiring tissues)

Question 11

Haemoglobin + Oxygen?

Answer 11

Oxyhaemoglobin

Question 12

How do you calculate percentage saturation of haemoglobin with oxygen?

Answer 12

( Oxygenated haemoglobin / maximum saturation ) x 100

Question 13

What is cooperative oxygen loading?

Answer 13

When the first O2 molecule alters the tertiary structure of the Hb molecule. This exposes the 2nd and 3rd O2 binding sites. This makes it easier for 2nd and 3rd O2 molecules to bind and load.

Question 14

What is partial pressure of Oxygen? (pO2 / kPa)

Answer 14

The amount of oxygen in a mixture of gases or a solution

Question 15

Heat from respiration helps mammals to maintain a constant body temperature.

Use this information to explain the relationship between the surface area to volume ratio of mammals and the oxygen dissociation curves of their haemoglobins.
(5)

Answer 15

Smaller mammal has greater surface area to volume ratio;
Smaller mammal/larger SA:Vol ratio more heat lost (per unit body mass);
Smaller mammal/larger SA:Vol ratio has greater rate of respiration/metabolism;
Oxygen required for aerobic respiration;
(Haemoglobin) releases more oxygen / oxygen released more readily / haemoglobin has lower affinity;