Mass transport

Question 1

Describe the structure of haemoglobin.

Answer 1

Globular, water soluble. Consists of 4 polypeptide chains, each carrying a
haem group (quaternary structure).

Question 2

Describe the role of haemoglobin.

Answer 2

Present in red blood cells. Oxygen molecules bind to the haem groups and are carried around the body to where they are needed in respiring tissues.

Question 3

Name three factors affecting oxygen-haemoglobin

binding.

Answer 3

1. Partial pressure/ concentration of oxygen.
2. Partial pressure/ concentration of carbon dioxide.
3. Saturation of haemoglobin with oxygen.

Question 4

How does partial pressure of oxygen affect oxygen-haemoglobin binding?

Answer 4

As partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases, so oxygen binds tightly to haemoglobin.
When partial pressure is low, oxygen is released from haemoglobin.

Question 5

How does partial pressure of carbon dioxide affect

oxygen-haemoglobin binding?

Answer 5

As partial pressure of carbon dioxide increases, the conditions become acidic causing haemoglobin to change shape.
The affinity of haemoglobin for oxygen therefore decreases, so oxygen is released from haemoglobin. This is known as the Bohr effect.

Question 6

How does saturation of haemoglobin with oxygen

affect oxygen-haemoglobin binding?

Answer 6

It is hard for the first oxygen molecule to bind.
Once it does, it changes the shape to make it easier for the 2nd and 3rd molecules to bind, known as positive cooperativity.
It is then slightly harder for the 4th oxygen molecule to bind because there is a low chance of finding a binding site.

Question 7

Explain why oxygen binds to haemoglobin in the lungs.

Answer 7

● Partial pressure of oxygen is high.
● Low concentration of carbon dioxide in the lungs, so affinity is high.
● Positive cooperativity (after the first oxygen molecule binds, binding of subsequent molecules is easier).

Question 8

Explain why oxygen is released from haemoglobin in respiring tissues.

Answer 8

● Partial pressure of oxygen is low

● High concentration of carbon dioxide in respiring tissues, so affinity decreases.

Question 9

What do oxyhaemoglobin dissociation curves show?

Answer 9

Saturation of haemoglobin with oxygen (in %), plotted against partial pressure of oxygen (in kPa).
Curves further to the left show the haemoglobin has a higher affinity for oxygen.

Question 10

How does carbon dioxide affect the position of an

oxyhaemoglobin dissociation curve?

Answer 10

Curve shifts to the right because haemoglobin’s affinity for oxygen has
decreased.

Question 11

Name three common features of a mammalian

circulatory system.

Answer 11

1. Suitable medium for transport, water-based to allow substances to dissolve.
2. Means of moving the medium and maintaining pressure throughout the body, such as the heart.
3. Means of controlling flow so it remains unidirectional, such as valves.

Question 12

Relate the structure of the chambers to their function.

Answer 12

● Atria: thin-walled and elastic, so they can stretch when filled with blood
● Ventricles: thick muscular walls pump blood under high pressure.
-The left ventricle is thicker than the right because it has to pump blood all the way around the body.

Question 13

Relate the structure of the vessels to their function.

Answer 13

● Arteries:
-thick walls to handle high pressure without tearing
-muscular and elastic to control blood flow.
● Veins:
-thin walls due to lower pressure
-valves to prevent backflow of blood
-less muscular and elastic tissue as they don’t have to control blood flow.

Question 14

Why are two pumps (left and right) needed instead of one?

Answer 14

To maintain blood pressure around the whole body.
When blood passes through the narrow capillaries of the lungs, the pressure drops sharply and therefore would not be flowing strongly enough to continue around the whole body.
Therefore it is returned to the heart to increase the pressure

Question 15

Describe what happens during cardiac diastole.

Answer 15

1. The heart is relaxed.
2. Blood enters the atria, increasing the pressure and pushing open the atrioventricular valves.
3. This allows blood to flow into the ventricles.
4. Pressure in the heart is lower than in the arteries, so semilunar valves remain closed.

Question 16

Describe what happens during atrial systole.

Answer 16

The atria contract, pushing any remaining blood into the ventricles.

Question 17

Describe what happens during ventricular systole.

Answer 17

1. The ventricles contract.
2. The pressure increases, closing the atrioventricular
   valves to prevent backflow, and opening the semilunar valves.
3. Blood flows into the arteries.

Question 18

How is the structure of capillaries suited to their

function?

Answer 18

● Walls are only one cell thick; short diffusion pathway.
● Very narrow, so can permeate tissues and red blood cells can lie flat against the wall, effectively delivering oxygen to tissues.
● Numerous and highly branched, providing a large surface area.

Question 19

What is tissue fluid?

Answer 19

A watery substance containing glucose, amino acids, oxygen, and other nutrients.
It supplies these to the cells, while also removing any waste materials.

Question 20

How is tissue fluid formed?

Answer 20

As blood is pumped through increasingly small vessels, this creates hydrostatic pressure which forces fluid out of the capillaries.
It bathes the cells, and then returns to the capillaries when the hydrostatic pressure is low enough.