3.4.1 Mass transport in animals

Question 1

Describe the structure of haemoglobin

Answer 1

Globular, water soluble. Consists of four polypeptide chain, each carrying a haem group

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, known as loading. 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 shape to make it easier for the second and third molecules to bind, known as positive cooperativity. It is then slightly harder for the fourth 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 tissue

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 some 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

Name the two chambers of the heart

Answer 12

Atria and ventricles

Question 13

Relate the structure of the atria to its function

Answer 13

Thin-walled and elastic, so they can stretch when filled with blood

Question 14

Relate the structure of the ventricles to its function

Answer 14

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 15

Name the two vessels of the heart

Answer 15

Arteries and veins

Question 16

Relate the structure of arteries to their function

Answer 16

Thick walls to handle high pressure without tearing, and are muscular and elastic to control blood flow

Question 17

Relate the structure of veins to their function

Answer 17

Thin walls due to lower pressure, therefore requiring valves to ensure blood doesn’t flow backwards. Have less muscular and elastic tissue as they don’t have to control blood flow

Question 18

Why are two pumps needed instead of one?

Answer 18

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 19

Describe what happens during cardiac diastole

Answer 19

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

Question 20

Describe what happens during atrial systole

Answer 20

The atria contract, pushing any remaining blood into the ventricles

Question 21

Describe what happens during ventricular systole

Answer 21

The ventricles contract. The pressure increases, closing the atrioventricular valves to prevent backflow, and opening the semi-lunar valves. Blood flows into the arteries

Question 22

Name the nodes involved in heart contraction

Answer 22

• Sinoatrial node (SAN)
• Atrioventricular node (AVN)

Question 23

Where is the sinoatrial node located?

Answer 23

Wall of the right atrium

Question 24

Where is the atrioventricular node located?

Answer 24

In between the two atria

Question 25

What does myogenic mean?

Answer 25

The heart’s contraction is initiated from within the muscle itself, rather than by nerve impulses

Question 26

Explain how the heart contracts

Answer 26

• SAN initiates and spreads impulse across the atria, so they contract
• AVN receives, delays, and then conveys the impulse down the bundle of His
• Impulse travels into the Purkinje fibres which branch across the ventricles, so they contract from the bottom up

Question 27

Why does the impulse need to be delayed?

Answer 27

If the impulse spread straight from the atria into the ventricles, there would not be enough time for all the blood to pass through and for the valves to close

Question 28

Describe the structure of capillaries

Answer 28

• Walls are only one cell thick
• Very narrow
• Numerous and highly branched

Question 29

How is the structure of capillaries suited to their function?

Answer 29

• 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 30

What is tissue fluid?

Answer 30

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

Question 31

How is tissue fluid formed?

Answer 31

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