Oxygen dissociation

Question 1

What is partial pressure of oxygen?

Answer 1

Hb saturation depends on the partial pressure of oxygen. The partial pressure of oxygen is a measure of oxygen concentration

The greater the concentration of dissolved oxygen in cells = the higher the partial pressure

Haemoglobin affinity for oxygen varies depending on the partial pressure of oxygen

Oxygen loads onto Hb to form oxyhaemoglobin where there is a high partial pressure pO2.
Oxyhaemoglobin unloads oxygen where there is a low partial pressure pO2

Question 2

How is oxygen dissociation in the lungs?

Answer 2

Oxygen enters the blood capillaries at the alveoli in the lungs. Alveoli have a high pO2, so the oxygen loads onto the Hb to form oxyhemoglobin

Question 3

How is oxygen dissociation in body cells?

Answer 3

Cells carry out respiration, which requires oxygen, this lowers the body cells pO2
Red blood cells deliver the oxyhaemoglobin to the respiring tissues, where it unloads the oxygen.
The Hb then returns to the lungs to pick up more oxygen

Question 4

Outline oxygen dissociation curves

Answer 4

A dissociation curve shows how saturated the haemoglobin is with oxygen at any given partial pressure
100% saturation = every Hb molecule is carrying the maximum of 4 molecules of oxygen.
0% saturation = none of the Hb molecules are carrying any oxygen

Question 5

Outline pO2 being high in the lungs

Answer 5

Hb has a high affinity for oxygen, so it readily combines with oxygen
Hb has a high saturation with oxygen

Question 6

Outline pO2 being low in respiring tissues

Answer 6

Hb has a low affinity for oxygen, so it releases oxygen readily rather than combine with it
Hb has a low saturation of oxygen.

Question 7

Outline the Bohr effect

Answer 7

The exact position of this curve depends on a number of factors, including the partial pressure of carbon dioxide, temperature and pH

Question 8

Partial pressure of carbon dioxide

Answer 8

The partial pressure of carbon dioxide (pCO2) measures the concentration of CO2 in a cell

When cells respire, they produce carbon dioxide which raises the pCO2

As pCO2 levels increase the rate at which oxygen is unloaded increases

This means that the rate at which oxyhaemoglobin dissociates to form Hb increases, meaning more oxygen is released. - when this happens the dissociation curve shifts to the right

This is called the Bohr effect

Hb gives up oxygen more readily at high partial pressure of CO2

Question 9

Explain why training at high altitudes might increase a runners race performance at sea level

Answer 9

High altitudes have lower partial pressure of oxygen therefore more red blood cells are made to carry enough oxygen.
When the runner returns to sea level, they have more red blood cells so more oxygen is carried than normal meaning aerobic respiration continues longer, and more energy is released for use by muscles