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A* A level Biology Summary notes mass transport
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Mass transport (3.3.4)Describe the structure of haemoglobin?
A protein with a quaternary structure that consists of 4 polypeptide chains- 2 alpha-globin and 2
beta-globin. Each polypeptide chain is associated with a haem (non-protein group) which contains an
Fe2+ ion.
Why are haemoglobin molecules soluble in water?
Due to their metabolic activity, they are globular proteins therefore have a spherical shape. The
hydrophobic R groups point inwards towards the centre of the molecule, and the hydrophilic R
groups point towards the outside of the molecule, so they can form hydrogen bonds with
surrounding water molecules.
Why is this important?
Because haemoglobin molecules are proteins associated with blood.
What is haemoglobins role?
The transport of oxygen. The haemoglobin must be able to load with oxygen at the lungs or gills, and
then unload once red blood cells reach the respiring tissues.
How does it carry out this role?
Each Fe2+ ion in the haem groups on the outside of the polypeptide chain will bind to one oxygen
atom. Each haem group has a high affinity (strong attraction) to oxygen, the high affinity allows the
haem groups to load with oxygen at the lungs. Oxygen and haemoglobin bind to form
oxyhaemoglobin (the red pigment synonymous with blood).
What is the oxyhaemoglobin dissociation curve?
A curve that plots the partial pressure of oxygen against the proportion of haemoglobin in its
saturated form.
Describe and explain the oxyhaemoglobin dissociation curves shape?
S- shaped because at a low partial pressure, there is low saturation at first because the haemoglobin
molecules with a high affinity for oxygen are in the centre of the molecule. As the partial pressure
increases, the first haem group binds to an oxygen atom causing a conformational change, which is a
change in the tertiary structure of haemoglobin which uncovers a second binding site making it
easier for the second molecule of haemoglobin to bind (cooperative nature of binding), as
haemoglobin approaches 100% saturation, the curve levels off.
How does a high concentration of CO2 affect haemoglobin?
Causes haemoglobin molecules to have a lower affinity for oxygen.
Where and how does CO2 affect haemoglobin?
At the gas exchange surface, the level of CO2 is low causing haemoglobin molecules to have a high
affinity whereas at the respiring tissues the level of CO2 is high causing haemoglobin molecules to
have a low affinity.
, Where and how do haemoglobin molecules load with oxygen?
Haemoglobin loads with oxygen at the gas exchange surface in the lungs as there is a low
concentration of CO2 because CO2 is constantly removed, therefore the pH is high which causes a
change in shape of the haemoglobin molecule that allows it to have a high affinity for oxygen (loads
with oxygen readily and does not release oxygen during transportation)
Where and how do haemoglobin molecules load with oxygen?
The respiring tissues. When haemoglobin gets to the respiring tissues, the concentration of CO2 is
high therefore the pH of the blood in tissues is low which causes a change in shape that gives the
haemoglobin molecule a low affinity allowing it to unload oxygen easily to the respiring tissues.
What does a higher rate of respiration cause?
The higher the rate of respiration, the more CO2 the tissues produce, the lower the pH of blood in
tissues, the greater the haemoglobin shape changes, the more readily oxygen is unloaded, and the
more oxygen is available for respiration.
What is the heart?
The heart is an organ that pumps blood around the body in a double circulatory system.
What is the right ventricle?
The chamber of the heart that pumps blood to the lungs for gas exchange- pulmonary circulation.
What is the left ventricle?
The chamber of the heart that pumps blood around the rest of the body- systemic circulation.
What are the coronary arteries?
The blood vessels that supply the heart muscle with oxygen and glucose for respiration.
Why does the left ventricle have a thicker muscular wall than the right ventricle?
As it ejects blood at a very high-pressure to pump blood further right to extremities of the body.
Why does the right ventricle have a less thick muscular wall than the left ventricle?
As it pumps blood at low pressure to maximise gas exchange in the short distance to the lungs and
also to prevent damage to the capillaries which do not have walls containing collages fibres to
withstand high pressure.
What happens if the coronary arteries are blocked?
They cannot supply oxygen and glucose to the heart muscle which it requires to contract. Therefore,
a myocardial infarction (heart attack) occurs which is when the heart muscle dies.
Why do mammals have a double circulatory system?
They are too large to reply on diffusion therefore they need a circulatory system to move substances
around the body. It is called a double circulatory system because blood passes through twice-
pulmonary circulation and systemic circulation.
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