3.4 mass transport in animals

Question 1

Why is the heart inverted?

Answer 1

Because it is from the point of view of a persons heart inside

Question 2

Describe the structure of haemoglobin

Answer 2

-Globular, water soluble
-consists of four polypeptide chains, each carrying a haem group (quaternary structure)

Question 3

Describe the role of haemoglobin

Answer 3

-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 4

Name the 3 factors affecting oxygen-haemoglobin binding

Answer 4

-partial pressure of oxygen
-partial pressure of carbon dioxide
-saturation of haemoglobin with oxygen

Question 5

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

Answer 5

-As pp of oxygen increases, the affinity of haemoglobin for oxygen also increases so oxygen binds tightly to haemoglobin
-When pp is low, oxygen is released from haemoglobin

Question 6

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

Answer 6

-As pp of carbon dioxide increases, the conditions become more acidic causing haemoglobin to change shape
-The affinity of haemoglobin for oxygen therefore decreases, so oxygen is released form haemoglobin (Bohr affect)

Question 7

How does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?

Answer 7

-Hard for the first oxygen molecule to bind
-Once it does, haemoglobin changes shape to make it easier for the second and third molecules to bind (positive cooperativity)
-Then, slightly harder for the fourth oxygen molecule to bind because there is a low chance of finding a binding site

Question 8

Explain why oxygen binds to heaemoglobin in the lungs

Answer 8

-Pp of oxygen is high
-Pp of carbon dioxide in the lungs is low, so high affinity
-Positive cooperation (after first oxygen molecule, binding of subsequent molecules is easier

Question 9

Explain why oxygen is released from haemoglobin in respiring tissues

Answer 9

-Pp of oxygen is low
-Pp of carbon dioxide is high, so affinity decreases

Question 10

What do oxyhaemoglobin dissociation curves show?

Answer 10

-Saturation of haemoglobin with oxygen (in %) plotted against pp of oxygen (in kPa)
-Curves further to the left showing the haemoglobin has a higher affinity for oxygen

Question 11

How does carbon dioxide affect the position of an oxyhaemoglobin dissociation curve?

Answer 11

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

Question 12

Name 3 common features of a mammalian circulatory system

Answer 12

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

Question 13

Relate the structure of the chambers to their function

Answer 13

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 right because it has to pump blood all the way around the body

Question 14

Relate veins and arteries structure to function

Answer 14

Arteries-thick walls to handle high pressure without tearing, and are muscular and elastic to control blood flow
Veins-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 15

Why are two pumps needed instead of one

Answer 15

-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 16

What happens during cardiac diastole

Answer 16

-The heart is relaxed
-Blood enters the atria, increasing the pressure and pushing open the AV valves
-This allows blood to flow into the ventricles
-Pressure in the heart is lower than in the arteries, so semilunar valves remain shut

Question 17

What happens during atrial systole?

Answer 17

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

Question 18

What happens during Ventricular systole?

Answer 18

-The ventricles contract
-The pressure increases, closing the atrioventricular valves to prevent backflow
-Opening of semilunar valves
-Blood flows into the arteries

Question 19

Name the nodes involved in the heart and where they are situated

Answer 19

-Sinoatrial node (SAN)=wall of the right atrium
-Atrioventrular node (AVN)=in between the two atria

Question 20

What does myogenic mean?

Answer 20

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

Question 21

How does the heart contract?

Answer 21

-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 down the purkinje fibres which branch across the ventricles, so they contract from the bottom up

Question 22

Why does the impulse need to be delayed when the AVN receives it?

Answer 22

-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 23

How is structure of capillaries related to function?

Answer 23

-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 24

What is tissue fluid?

Answer 24

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

Question 25

How is tissue fluid formed

Answer 25

-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