3.3.4 Mass transport in animals

Question 1

Describe the structure of haemoglobin

Answer 1

Globular, water soluble. Consists of 4 polypeptide chains, each carry a haem group

Question 2

Describe the role of haemoglobin

Answer 2

Present in RBC
Oxygen molecules bind to the haem groups and are carried around the body to where they are needed in respiring tissues

Question 3

Name 3 factors affecting oxygen-haemoglobin binding

Answer 3

1. Partial pressure of oxygen
2. Partial pressure 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 a 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 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 conc of CO2 in lungs so affinity is high
Positive cooperativity

Question 8

Explain why oxygen is released from haemoglobin in respiring tissues

Answer 8

Partial pressure of oxygen is low
High conc of CO2 in respiring tissues so affinity decreases

Question 9

What do oxyhaemoglobin dissociation curves show

Answer 9

Saturation of haemoglobin with oxygen plotted against partial pressure of oxygen. Curves further to the left to show the haemoglobin has a higher affinity for oxygen

Question 10

How does CO2 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

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 functions

Answer 13

Arteries have thick walls to handle high pressure without tearing, and are muscular and elastic to control blood flow
Veins have thin walls due to lower pressure therefore requiring valves to prevent the backflow of blood. Have less muscular and elastic tissue as they dont have to control blood flow

Question 14

Why are 2 pumps 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 its returned to the heart to increase the pressure

Question 15

Describe what happens during cardiac diastole

Answer 15

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 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

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

Question 18

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

Answer 18

Sinoatrial node (SAN) = wall of right atrium
Atrioventricular node (AVN) = inbetween the 2 atria

Question 19

What does myogenic mean

Answer 19

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

Question 20

Explain how the heart contracts

Answer 20

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 21

Why does the impulse need to be delayed

Answer 21

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 22

How is the structure of capillaries suited to their function

Answer 22

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

Question 23

What is tissue fluid

Answer 23

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

Question 24

How is tissue fluid formed

Answer 24

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

Question 25

Explain how valves maintain blood flow in one direction (right)

Answer 25

(happens on either side this is for right) Blood enters right atrium from vena cava
Atrium contracts the volume decreases so pressure increases, when pressure in atrium is greater than ventricle then the atrioventricular valve opens
Blood moves into right ventricle
Right ventricle contracts so volume decreases so pressure increases, pressure in ventricle is greater than the atrium so atrioventricular valve closes
Pressure in ventricle is greater than pulmonary artery so semi lunar valve opens
Blood moved into pulmonary artery
Pressure in pulmonary artery greater than ventricle so semi lunar valve closes