Module 3: Transport in Animals

Question 1

Why do organisms require a mass transport system?

Answer 1

Organisms require oxygen and glucose to produce energy for aerobic respiration.

Small organisms such as bacteria, can obtain these by diffusion due to short diffusion pathway/distance

However, large organisms have a large diffusion distances meaning that diffusion would be too slow to reach the cells in the centre of the body. Therefore they require mass transport systems.

Question 2

Why do multicellular organisms require a mass transport system?

Answer 2

They are relatively big, have a low surface area to volume ratio and a higher metabolic rate.

Question 3

What is the transport system in mammals and describe its function.

Answer 3

The circulatory system in mammals uses blood to carry glucose and oxygen around the body.

It also carries hormones, antibodies (to fight disease) and waster products like CO2

Question 4

Describe the single circulatory system and give an example.

Answer 4

In a single system, blood only passes through the heart once for each complete circuit of the body.

Example: Fish have a single transport system.

The heart pumps deoxygenated blood to the gills (to pick up oxygen) and then the gills pump oxygenated blood through the rest of the body (to deliver the oxygen) before returning back to the heart in a single circuit.

Question 5

Describe a double circulatory system and give an example.

Answer 5

Here, the blood passes through the heart twice for each complete circuit of the body.

Example: Mammals.

The right side of the heart pumps deoxygenated blood to the lungs (to pick up oxygen). From the lungs, the now oxygenated blood travels to the left side of the heart, which pumps it to the rest of the body. When deoxygenated blood from the rest of the body returns back to the heart, it enters the right side again.

The two loops are known as the pulmonary system (to the lungs) and the systemic system (to the body).

Question 6

Describe closed circulatory systems and give an example.

Answer 6

Blood is enclosed inside blood vessels.

Example: Fish and mammals.

In fish, the heart pumps deoxygenated blood into arteries. These branch out into millions of capillaries. Substances such as oxygen and glucose diffuse from the blood in the capillaries into the body cells, (blood becomes oxygenated) but the blood stays inside the blood vessels as it circulates. Veins takes blood back to the heart.

Question 7

Describe open circulatory systems and give an example.

Answer 7

Here, blood isn’t enclosed in blood vessels all the time. Instead, it flows freely through the body cavity.

Example: Insects.

1) The segmented heart pumps blood forwards.
2) The blood is pumped into a single main artery.
3) The main artery opens up into the body cavity.
4) The blood flows back through the body cavity.
5) The blood returns to heart through valves.

Question 8

What are the 5 types of blood vessels?

Answer 8

Arteries.

Arterioles.

Capillaries.

Venules.

Veins.

Question 9

Describe the structure and function of Arteries.

Answer 9

Function: They carry blood from the heart to the rest of the body- different organs.

Structure: Their walls are thick, muscular and have elastic tissue to stretch and recoil as the heart beats, which helps to maintain the high pressure.

The inner lining of the arteries, called the endothelium, is folded which allows the artery to expand (elastic recoil) which also helps it to withstand the high pressure.

The small lumen ensures a high pressure is maintained.

All arteries carry oxygenated blood, except for the pulmonary arteries, which take deoxygenated blood to the lungs.

Question 10

Describe the structure and function of Arterioles.

Answer 10

Function: Controls the amount of blood flowing throughout the body.

Structure: Arteries branch into arterioles, which are much smaller than arteries.

They have a layer of smooth muscle, but they have less elastic tissue.
The smooth muscle allows them to expand or contract, thus controlling the amount of blood flowing to tissues.

Question 11

Describe the structure and function of Capillaries.

Answer 11

Function: allow the exchange of substances such as oxygen and glucose between the blood and the body’s cells.

Arterioles branch into capillaries (smallest blood vessels).

Small holes (pores) enable the exchange of substances.

Walls are just one cell thick which reduces the diffusion distance for these substances.

Question 12

Describe the structure and function of venules.

Answer 12

Function: moves blood that contains waste and lacks oxygen from your capillaries to your veins.

Structure: Have thin walls that contain some muscle cells. Venules join together to form veins.

Question 13

Describe the structure and function of veins.

Answer 13

Function: Carry blood from the organs of the body towards the heart.

Blood is flowing at a much lower pressure so veins have a large lumen and much thinner walls containing little elastic fibres or muscle tissue.

Valves prevent the slow-moving blood from flowing backwards.

The contraction of nearby body muscles helps blood to flow through veins.

Question 13

What is tissue fluid and how is it made?

Answer 13

It is the fluid that surrounds cells in tissues.

It is made up of the substances that are small enough to move out of the capillary, such as water, oxygen, glucose and mineral ions.

It also contains the waste products released from cells, like carbon dioxide, water and urea.

It doesn’t contain things that are too big to be forced out of the capillary, so there are no red blood cells or large proteins.

In a capillary bed (the network of capillaries in an area of tissue), substances move out of the capillaries, into the tissue fluid, by pressure filtration.

Question 14

What is pressure filtration?

Answer 14

At the start of the capillary bed, nearest the arteries, the hydrostatic pressure (pressure exerted by a liquid) inside the capillaries is greater than the hydrostatic pressure in the tissue fluid.

This difference in hydrostatic pressure forces fluid out of the capillaries (down a pressure gradient) and into the spaces around the cells, forming tissue fluid.

As fluid leaves, the hydrostatic pressure reduces in the capillaries- so the hydrostatic pressure is much lower at the end of the capillary bed that’s nearest to the venules.

As water leaves the capillaries, the concentration of plasma proteins in the capillaries increases and the water potential decreases. Plasma proteins in the capillaries generate a form of pressure called oncotic pressure- so at the venule end of the capillary bed there is a high oncotic pressure and a low water potential.

As the water potential in the capillaries is lower than the water potential in the tissue fluid, some water re-enters the capillaries from the tissue fluid at the venule end by osmosis.

Question 15

Explain what happens to excess tissue fluid.

Answer 15

Not all tissue fluid re-enters the capillaries at the vein end of the capillary bed- some excess tissue fluid is left over.

This extra fluid eventually gets returned to the blood through the lymphatic system- a kind of drainage system, made up of lymph vessels.

Question 16

Explain the lymphatic system.

Answer 16

Excess tissue fluid passes into lymph vessels. The smallest lymph vessels are lymph capillaries. Once it is inside, it is called lymph.

Valves in the lymph vessels stop the lymph going backwards.

Lymph gradually moves towards the main lymph vessels in the thorax (chest cavity)

Here, it is returned to the blood, near the heart.

Question 17

Explain the differences in the composition of blood, tissue fluid and lymph.

Answer 17

RED BLOOD CELLS: are present in the blood but cannot be tissue fluid or lymph due to them beings too big to get through the capillary walls into tissue fluid.

WHITE BLOOD CELLS: are present in the blood, very few turn into tissue fluid. Most white blood cells are in the lymph system. They only enter tissue fluid when there is an infection.

PLATELETS: present in the blood and not present in the tissue fluid or lymph. They are only present in tissue fluid if the capillaries are damaged.

PROTEINS: present in the blood and very few are turned into tissue fluid, lymph only contains the antibodies. This is because most plasma proteins are too big to get through capillary walls.

WATER: present in the blood, tissue fluid and lymph. Tissue fluid and lymph have a higher water potential than blood.

DISSOLVED SOLUTES: present in all blood, tissue fluid and lymph. This is because solutes can move freely between blood, tissue fluid and lymph.

Question 18

Describe the components of an external structure of the heart.

Answer 18

Consists of:

Superior vena cava
Inferior vena cava
Aorta
Right atrium
Coronary artery
Right ventricle
Vena cava
Pulmonary artery
Left atrium
Pulmonary veins
Left ventricle.

Question 19

Describe the components of an internal structure of the heart.

Answer 19

Consists of:

Superior vena cava

Inferior vena cava

Right atrium

Semi- lunar valve

Atrioventricular valve

Right ventricle

Left ventricle

Cords (valve tendons)

Atrioventricular valve

Semi- lunar valve

Left atrium

Pulmonary veins

Aorta

Pulmonary artery.

Question 20

Describe the structure and function of the heart.

Answer 20

The heart is made up of four chambers divided into two sides. The left side of the heart has a thicker wall, as it needs to pump more strongly to deliver blood all around the body (whereas the right side just needs to send the blood to the lungs). The left side carries oxygenated blood whereas the right side carries deoxygenated blood.

Question 21

Explain how the heart pumps blood to the left side of the heart and to the rest of the body.

Answer 21

The chambers at the top are called atria and these chambers receive the blood from the veins supplying the heart.

Blood flows from the atria to the ventricles, which are separated from the atria by atrioventricular valves to prevent blood flowing in the opposite direction.

There are another set of valves between the ventricles and the arteries which are called the semi-lunar valves as they look like little half-moons.

The main artery which takes oxygenated blood from the left side of the heart to the rest of the body is called the aorta whereas the artery which delivers deoxygenated blood between the right side of the heart and the lungs is called the pulmonary artery.

The major vein which returns blood from the body to the right side of the heart is the vena cava and the vein which ferries blood from the lungs to the heart is called the pulmonary vein.

The heart muscle itself also needs its own blood supply, so that it can get plenty of oxygen and glucose to keep respiring and keep pumping - these are called the coronary arteries. It’s a blockage in these coronary arteries which leads to a heart attack.

Question 22

Describe the practical for the dissection of a mammalian heart.

Answer 22

• Dissecting instruments
  should be clean and sharp.

Identify the aorta and coronary arteries.
* Some hearts are slit which makes it difficult to see the
valves and to flow the water through.
* Specialist suppliers can supply whole hearts or they can
be bought as part of a ‘full pluck’ which has the lungs
and trachea attached so the heart remains intact.
The heart is open like a butterfly structure so the
ventricular walls and internal structures can be easily
seen.
* To open the heart, start at the aorta and cut around the
outside edge of the heart.
* Lay the heart flat on a dissection board and label the
structures.
* Dispose of all items including gloves and paper towels
in a special disposal bag.

Question 23

What is the Cardiac cycle?

Answer 23

The cardiac cycle is a coordinated sequence of contractions and relaxations by the heart muscle which causes blood to move from the atria, into the ventricles and then the arteries.

The volumes of the atria and ventricles change as they contract and relax, altering the pressure in each chamber. This causes valves to open and close, which directs the blood flow through the heart.
If you listen to a human heartbeat you can hear a ‘lub-dub’ sound. The first ‘lub’ sound is caused by the atrioventricular valves closing. The second ‘dub’ sound is caused by the semi-lunar valves closing.

Muscle contractions are referred to as systole and relaxation is referred to as diastole.

It occurs in the three stages:

Question 24

Explain the first stage of the cardiac cycle.

Answer 24

1. The atria contract, ventricles relax. (ATRIAL SYSTOLE)

The ventricles are relaxed. The atria contract, decreasing the volume of the chambers and increasing the pressure inside the chambers.

This pushes the blood into the ventricles, through the atrioventricular valves (already open)

There’s a slight increase in ventricular pressure and chamber volume as the ventricles receive the ejected blood from the contracting atria.

Question 25

Explain the second stage of the cardiac cycle.

Answer 25

2. The ventricles contract, the atria relaxes. (Ventricular systole)

The atria relaxes and the ventricles contract, decreasing their volume and increasing their pressure.

The pressure becomes higher in the ventricles than the atria, which forces the AV valves shut to prevent back-flow.

The pressure in the ventricles is also higher than in the aorta and the pulmonary artery, which forces open the SL valves and blood is forced out into theses arteries.

Question 26

Explain the third stage of the cardiac cycle.

Answer 26

3. Ventricles relax and the atria relaxes. (Diastole)

The ventricles and the atria both relax. The higher pressure in the pulmonary artery closes the SL valves to prevent back-flow into the ventricles.

Blood returns to the heart and the atria fill again due to higher pressure in the vena cava and the pulmonary vein.

In turn this starts to increase the pressure of the atria.

As the ventricles continue to relax, their pressure falls below the pressure of the atria and so the AV valves open.

This allows blood to flow passively (without being pushed by atrial contraction) into the ventricles from the atria. the atria contract, and the whole process begins again.

Question 27

What is cardiac output and how do you calculate?

Answer 27

Cardiac output is the volume of blood pumped by the heart per minute (measured in Cm3 min-1)

[CARDIAC OUTPUT = HEART RATE X STROKE VOLUME]

HEART RATE: The number of beats per minute (bpm)

STROKE VOLUME: The volume of blood pumped during each heartbeat, measured in cm3

Question 28

What muscle is ‘Myogenic’ and what does this mean?

Answer 28

Cardiac muscle is ‘myogenic’ which means it can contract and relax on its own accord without receiving signals from nerve.

This pattern of contraction controls the regular heartbeat.

Question 29

What is the process that happens for a heartbeat to take place?

Answer 29

The process starts in the Sino-atrial node (SAN), which is in the wall of the right atrium. The SAN is like a pacemakers- its sets the rhythm of the heartbeat by sending regular waves of electrical activity over the atrial walls. This causes the right and left atria to contract at the same time.

A band of non-conducting collagen tissue prevents the waves of electrical activity from being passed directly from the atria to the ventricles. Instead, these waves of electrical activity are transferred from the SAN to the atrioventricular node (AVN).

The AVN is responsible for passing the waves of electrical activity on to the bundle of His. But there’s a slight delay before the AVN reacts, to make sure the ventricles contract after the atria have emptied.

The bundle of His is a group of muscle fibres responsible for conducting the waves of electrical activity to the finer muscle fibres in the right and left ventricles walls, called the Purkyne tissue.

The Purkyne tissue carries the waves of electrical activity into the muscular walls of the right and left ventricles, causing them to contract simultaneously, from the bottom up.

Question 30

What is an Electrocardiographs?

Answer 30

It is a machine that records the electrical activity of the heart.

Question 31

How does an Electrocardiographs work?

Answer 31

Whenever a part of the heart contracts, the membrane of muscle cells becomes depolarised (it loses charge) and repolarises (gains charge) when the muscle relaxes.

This change in charge in the heart muscle can be detected by an electrocardiograph, which uses electrodes placed against the patient’s chest.

The change in electrical activity is displayed as an electrocardiogram (ECG) which can be used by doctors to diagnose heart problems.

Question 32

Explain what you would see on a normal ECG trace and what each section means.

Answer 32

The first, small bump on an ECG is called the P wave which is caused by the atria contracting (depolarisation).

The large, sharp spike is called the QRS complex and is caused by the ventricular contraction.

The final bump is referred to as the T wave and results from repolarisation of the ventricles as they relax.

You can pick out any of these points on the ECG to measure the time taken for one heart beat to occur - e.g. the time taken from one P wave to the next P wave.

The height of the wave is proportional to the strength of contraction - the higher the wave, the greater the depolarisation of the muscle cell and the stronger the contraction.

Question 33

How can you calculate heart rate?

Answer 33

you can use an ECG.

heart rate (bpm) = 60 / time taken for one heartbeat (s)

Question 34

What is Tachycardia?

Answer 34

This is when the heartbeat is too fast- around 120 beats per minute.

This is ok during exercise, however at rest it shows that the heart isn’t pumping blood efficiently.

Question 35

What is Bradycardia?

Answer 35

This is when the heartbeat is too slow- 50 beats per minute.

A heart rate this slow is normal in some people such as trained athletes.

However in others it can indicate a problem with the electrical activity of the heart.
For example there may be something preventing impulses from the SAN being passed on properly.

Question 36

What is an Ectopic Heartbeat?

Answer 36

This is an extra heartbeat that interrupts the regular rhythm.

It can be caused by an earlier contraction of the atria than in previous heartbeats.

However, it can also be caused by earlier contraction of the ventricles tool.

Occasional ectopic heartbeats in a healthy person do not cause problems.

Question 37

What is Fibrillation?

Answer 37

This is a really irregular heartbeat.

The atria or ventricles completely lose their rhythm and stop contracting properly.

It can result in anything from chest pain and fainting to lack of pulse and death.

Question 38

What is Haemoglobin?

Answer 38

It is a protein that has a quaternary structure.

Haemoglobin has 4 polypeptide chains that aren’t able to bind to oxygen alone, as it would chain the structure. Instead the polypeptide chains bind to prosthetic groups called haem groups that can bind to oxygen. The haem groups contain iron ions which allow bonds to form with oxygen.

Question 39

Describe the association and dissociation of Oxyhaemoglobin

Answer 39

In the lungs, oxygen joins to the iron in haemoglobin to form oxyhaemoglobin.

This is a reversible reaction- near the body cells, oxygen leaves oxyhaemoglobin and it turns back to haemoglobin.

When an oxygen molecule joins to haemoglobin, its referred to as association or loading, and when oxygen leaves oxyhaemoglobin it’s referred to as dissociation or unloading.

Hb + 4O2 = HbO8

Question 40

What does ‘affinity’ for oxygen mean?

Answer 40

This means the tendency a molecule has to bind with oxygen.

Question 41

Explain haemoglobin’s affinity for oxygen and pO2.

Answer 41

Haemoglobin’s affinity for oxygen varies depending on the conditions it’s in.

One of the conditions that affect haemoglobins affinity for oxygen is the partial pressure of oxygen (pO2). This is the measure of oxygen concentration.

The greater the concentration of dissolved oxygen in cells, the higher the partial pressure.

As pO2 increases, haemoglobins affinity for oxygen also increases. This is because oxygen loads onto haemoglobin to form oxyhaemoglobin where there’s a high pO2. Also, oxyhaemoglobin unloads its oxygen where there’s a lower pO2

Question 42

What does Positive Cooperativity mean?

Answer 42

This means when the binding or unbinding of one particle makes it easier for another to bind or unbind.

Question 43

Give an example of positive cooperativity in terms of haemoglobin and oxygen.

Answer 43

When an oxygen molecule binds to an iron atom in haemoglobin, the quaternary structure of haemoglobin changes.

This change in structure uncovers more of the iron atoms making it easier for another oxygen molecules to bind.

Question 44

What is oxygen association and disassociation?

Answer 44

Oxygen association: The process of oxygen binding to haemoglobin.

Oxygen disassociation: The process of oxygen unbinding to haemoglobin.

Question 45

Explain the process of oxygen loading and unloading in the lungs and respiring cells.

Answer 45

Oxygen enters blood capillaries at the alveoli in the lungs.

Alveoli have a high pO2, so oxygen loads onto haemoglobin to form oxyhaemoglobin. Positive cooperativity enables oxygen to rapidly associate to haemoglobin speeding up the transfer of oxygen from the air in the alveoli to our red blood cells.

When cells respire, they use up oxygen and this lowers the pO2. Red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads it’s oxygen.

The haemoglobin then returns to the lungs to pick up more oxygen.

Question 46

What is an oxygen Dissociation curve?

Answer 46

This shows how saturated (how full) the haemoglobin is with oxygen at any given partial pressure.

Question 47

Describe the shape of an oxygen dissociation curve and explain why.

Answer 47

It is an S- shape.

Where pO2 is high (lungs), haemoglobin has a high affinity for oxygen, so it has a high saturation of oxygen.

where pO2 is low (respiring tissues), haemoglobin has a low affinity for oxygen, so it has a low saturation of oxygen.

Question 48

How does the saturation of haemoglobin affect its affinity for oxygen?

Answer 48

When haemoglobin combines with the first oxygen molecule, its shape alters in a way that makes it easier for other molecules to join too.

As the haemoglobin starts to become saturated, it gets harder for more oxygen molecules to join.

As a result, the curve has a steep bit in the middle where it’s really easy for oxygen molecules to join, and shallow bits at each end where its harder.

When the curve is steep, a small change in pO2 causes a big change in the amount of oxygen carried by haemoglobin.

Question 49

What are the two types of haemoglobin?

Answer 49

1) Fetal haemoglobin - found in foetuses.

2) Adult haemoglobin - found in humans after birth.

Question 50

Explain Fetal haemoglobin affinity.

Answer 50

Fetal haemoglobin has a higher affinity for oxygen compared to adult haemoglobin.

This means that it binds more strongly, holding on to the oxygen as it makes its way around the mother’s body.

It ensures that it is still in the oxyhaemoglobin form by the time It gets past the placenta to reach the foetus.

If fetal haemoglobin had the same affinity for oxygen as adult haemoglobin its blood wouldn’t be saturated enough. On a dissociation curve, fetal haemoglobin lies slightly to the left.

At low pO2 in the placenta, fetal haemoglobin has a high affinity for oxygen, so oxygen loads.

Question 51

What is the Bohr effect?

Answer 51

The shift in the oxygen dissociation curve caused by changes in the concentration of carbon dioxide or the pH of the environment is called the Bohr effect.

When cells respire they produce CO2, which raises the partial pressure of CO2 (pCO2),

This increases the rate of oxygen unloading- the dissociation curve ‘shifts’ right (still same shape).

The saturation of blood with oxygen is lower for a given pO2, meaning that more oxygen is being released.

Question 52

What is the reason for the Bohr Effect?

Answer 52

More CO2 =More H+ ions= More acidic
Less CO2 =Less H+ ions+ Less acidic

The concentration of CO2 in the blood influences the pH of the blood.

This is because in our blood CO2 reacts with water to form H+ ions and the concentration of these ions determines the blood pH and therefore the acidity.

As the bloods pH increases (more alkaline), the shape of the haemoglobin changes, and it is easier for oxygen to associate.

Question 53

What is the Bohr effect beneficial for and why?

Answer 53

It is beneficial for exercise. Respiring muscle cells release CO2, which decreases the pH of the blood near the tissues. This causes oxyhaemoglobin to change shape, allowing oxygen to dissociate/unbind more readily

Question 54

Explain the reaction that takes in the blood with CO2.

Answer 54

In red blood cells, CO2 reacts with water to form carbonic acid- catalysed by the enzyme carbonic anhydrase.

CO2 + H2O —> H2CO3

Carbonic acid splits up into 2 ions - Hydrogen carbonate ions and H+ ions.

H2CO3 —> H+ + HCO3-

This increase in H+ ions (more acidic) causes oxyhaemoglobin to unload its oxygen so that haemoglobin can take up the H+ ions.

This forms a compound called haemoglobinic acid- This process also stops the H+ ions from increasing the cells acidity.
The HCO3- ions diffuse out of the red blood cells and are transported in the blood plasma.

Question 55

What is the Chloride shift?

Answer 55

When carbonic acid dissociates to H+ and HCO3- ions, the HCO£- ions diffuse out of the red blood cells, transported back to the lungs in the blood plasma.

This then results in the blood plasma being too negatively charged. So Cl- from the blood plasma diffuses out of the blood plasma and into the red blood cells.

When the blood reaches the lungs, the reversed reaction takes place. HCO3- diffuses out of the blood plasma into the red blood cells and the Cl- diffuses into the blood plasma.

The hydrogen ion (that remained in the blood) recombines with the hydrogen carbonate ion to form carbonic acid which splits back into carbon dioxide and water.

The carbon dioxide diffuses into the alveoli and is breathed out.