3.1.2 Transport in Animals

Question 1

What factors influence the need for a transport system?

Answer 1

• size
• surface area to volume ratio
• level of metabolic activity

Question 2

How does size influence the need for a transport system?

Answer 2

• cells in a large organism are further from its surface, so the diffusion pathway is increased
• diffusion rate is reduced, and too slow to supply all the requirements
• the outer layers of cells also use up the supplies, so that less will reach the cells deep inside the body

Question 3

How does surface area to volume ratio influence the need for a transport system?

Answer 3

• small animals have a large surface area to volume ratio
• therefore, for each gram of tissue in their body, they have a sufficient area of body surface through which exchange can occur
• however, larger animals have a smaller surface area to volume ratio, so each gram of tissue has a smaller area of body surface for exchange

Question 4

How do the levels of metabolic activity influence the need for a transport system?

Answer 4

• animals need energy from food, so that they can move around
• releasing energy from food by aerobic respiration requires oxygen
• if the animal is very active, its cells need good supplies of nutrients and oxygen to supply the energy for movement
• animals that keep themselves warm, such as mammals, need more energy

Question 5

What are some features of an effective transport system?

Answer 5

• a fluid or medium to carry nutrients, oxygen and wastes around the body (blood)
• a pump t create pressure that will push the fluid around the body (heart)
• exchange surfaces that enable substances to enter the blood and leave it again where they are needed (capillaries)

Question 6

What are some features of an efficient transport system?

Answer 6

• tubes or vessels to carry the blood by mass flow
• two circuits: one to pick up oxygen and another to deliver oxygen to the tissues

Question 7

Define single circulatory system

Answer 7

• one in which the blood flows through the heart once for each circuit of the body

Question 8

Define double circulatory system

Answer 8

• one in which the blood flows through the heart twice for each circuit of the body

Question 9

Which animals have a single circulatory system?

Answer 9

• fish

Question 10

What route does the circulatory system of fish take?

Answer 10

• heart → gills → body → heart

Question 11

What is pulmonary circulation?

Answer 11

• one of the circuits in the double circulatory system
• carries blood to the lungs to pick up oxygen

Question 12

What is systemic circulation?

Answer 12

• one of the circuits in the double circulatory system
• carries the oxygen and nutrients around the body to the tissues

Question 13

What route does blood take in a double circulatory system?

Answer 13

• heart → body → heart → lungs → heart

Question 14

Explain why the single circulatory system of fish is not as efficient as the double circulatory system

Answer 14

• the blood pressure drops as blood passes through the tiny capillaries of the gills
• blood has low pressure as it flows towards the body and will not flow very quickly
• the rate at which oxygen and nutrients are delivered to respiring tissues and CO₂ and urea are removed, is limited
• however, fish are not as metabolically active as mammals, as they do not maintain their body temperature
• so they need less energy and their system delivers sufficient oxygen and nutrients for their needs

Question 15

Explain the advantages of the double circulatory system

Answer 15

• the blood pressure must not be too high in the pulmonary circulation, otherwise it may damage the delicate capillaries in the lungs
• the heart can increase the pressure of the blood after it has passed through the lungs, so the blood is under higher pressure as it flows to the body and flows more quickly
• the systemic circulation can carry blood at a higher pressure than pulmonary circulation

Question 16

What is an open circulatory system

Answer 16

• blood is not held in blood vessels and instead circulates through the body cavity so that tissues and cells are bathed directly in blood

Question 17

Why is movement important for some animals with an open circulatory system?

Answer 17

• some animals require movement for blood to circulate around the body
• without movement, blood stops moving and transport of oxygen and nutrients stop

Question 18

Describe how blood is pumped in some animals with an open circulatory system

Answer 18

• e.g. locusts
• a long, muscular tube that lies under the dorsal surface of the body is much like the heart
• blood from the body enters the heart through pores called ostia
• heart then pumps the blood towards the head by peristalsis
• at the forward end of the heart, the blood simply pours out into the body cavity
• this circulation can continue when insect is at rest, but movement also affects

Question 19

Why do some larger and more active insects have open-ended tubes attached to the heart?

Answer 19

• these direct blood towards the active part of the body, such as wing and leg muscles

Question 20

What are the disadvantages of open circulatory systems?

Answer 20

• blood pressure is low
• blood flow is slow
• circulation of blood may be affected by body movements or lack of body movements

Question 21

What is the closed circulatory system?

Answer 21

• blood is held inside vessels
• in larger animals
• a separate fluid, called tissue fluid, bathes the tissues and cells

Question 22

Give advantages of a closed circulatory system

Answer 22

• higher pressure, so that blood flows more quickly
• more rapid delivery of oxygen and nutrients
• more rapid removal of carbon dioxide and other wastes
• transport is independent of body movements

Question 23

What is the structure and function of the endothelium?

Answer 23

• all types of blood vessels have an inner layer or lining, made of a single layer of cells
• thin later is particularly smooth in order to reduce friction with the flowing blood

Question 24

Describe the structure of arteries

Answer 24

• artery wall is thick because blood is at high pressure
• lumen is relatively small in order to maintain high pressure
• inner wall (consisting of three layers) is folded to allow lumen to expand as blood flow increases

Question 25

Describe the three layers of the inner wall of the arteries

Answer 25

• inner layer (tunica intima): consists of a thin layer of elastic tissue which allows the wall to stretch and then recoil to help maintain blood pressure
• middle layer (tunica media): consists of a thick layer of smooth muscle
• outer layer (tunica adventitia): a relatively thick layer of collagen and elastic tissues which provides strength to withstand the high pressure and recoil to maintain pressure

Question 26

Describe the structure and function of the arterioles

Answer 26

• arterioles are small blood vessels that distribute the blood from an artery to the capillaries
• arteriole walls contain a layer of smooth muscle
• contraction of this muscle will constrict the diameter of the arteriole
• this increases resistance to flow and reduces the rate of flow of blood
• constriction of the arteriole walls can be used to divert the flow of blood to regions of the body that are demanding more oxygen

Question 27

Describe the structure of capillaries

Answer 27

• they have very thin walls, allowing exchange of materials between the blood and tissue fluid
• lumen is very narrow:
• diameter is about the same as a red blood cell (7µm)
• red blood cells may be squeezed against the walls of the capillary as they pass along
• this helps the transfer of oxygen, as it reduces the diffusion path to the tissues
• also increases resistance and reduces the rate of flow
• walls consist of a single layer of flattened endothelial cells
• this reduces diffusion distance for the materials being exchanged
• walls are leaky which allow blood plasma and dissolved substances to leave the blood

Question 28

Describe the structure of venules

Answer 28

• from the capillaries, blood flows into small vessels called venules
• these collect the blood from the capillary bed and lead into the veins
• venule wall consists of thin layers of muscle and elastic tissue outside the endothelium and a thin outer layer of collagen

Question 29

Describe the structure and function of veins

Answer 29

• veins carry blood back to the heart
• the blood is at low pressure and walls do not need to be thick
• lumen is relatively large, in order to ease the flow of blood
• walls have thinner layers of collagen, smooth muscle and elastic tissue than in artery walls
• they do not need to stretch and recoil and are not actively constricted in order to reduce blood flow
• they contain valves to help the blood flow back to the heart and to prevent it flowing in the opposite direction
• as the walls are thin, the vein can be flattened by the action of surrounding skeletal muscle
• contraction of surrounding skeletal muscle applies pressure to the blood, forcing blood to move along in a direction determined by the valves

Question 30

What is in blood?

Answer 30

• plasma which contains:
• many dissolved substances
• oxygen, CO2, minerals, glucose, amino acids, hormones and plasma proteins
• cells:
• erythrocytes (red blood cells)
• varioous white blood cells (leucocytes)
• platelets

Question 31

Describe the formation of tissue fluid

Answer 31

• when an artery reaches the tissues, it branches into smaller arterioles, then into a network of capillaries. These eventually link up with venules to carry blood back to the veins. So, blood flowing into an organ or tissue is contained in capillaries
• at the arterial end of a capillary, the blood is at relatively high hydrostatic pressure
• this pressure pushes blood fluid out f the capillaries through the capillary wall as it leaves through tiny gaps between the cells in the capillary wall
• the fluid that leaves the blood consists of plasma with dissolved nutrients and oxygen. This is called mass flow.
• all red blood cells, platelets, plasma proteins and most white blood cells remain in blood as they are too large to pass through capillary wall gaps
• this tissue fluid surrounds the body cells, so exchange of gases and nutrients can occur across the plasma membranes
• this exchange occurs by diffusion, facilitated diffusion and active transport

Question 32

How does tissue fluid return to the blood?

Answer 32

• the blood pressure at the venous end of the capillary is much lower
• this allows some tissue fluid to return to the capillary carrying carbon dioxide and other waste substances into the blood
• but not all tissue fluid re-enters the blood

Question 33

Where else does tissue fluid go if not back into blood?

Answer 33

• some tissue fluid is directed into another tubular system called the lymph system or lymphatic system
• this drains excess tissue fluid out of the tissues and returns it to the blood system in the subclavian vein in the chest
• the fluid in the lymphatic system is called lymph and is similar in composition to tissue fluid
• it will contains more lymphocytes, as these are produced in the lymph nodes

Question 34

What are lymph nodes?

Answer 34

• they are swellings found at intervals along the lymphatic system
• they have an important part to play in the immune system

Question 35

What are the differences between plasma, tissue fluid and lymph?

Answer 35

Question 36

What influences the movement of fluid into and out of the capillary?

Answer 36

• hydrostatic pressure of the blood
• the hydrostatic pressure of the tissue fluid
• the oncotic pressure of solutes

Question 37

Describe the movement of fluid into and out of the capillary

Answer 37

• the hydrostatic pressure of the blood tends to push fluid out into the tissues
• the hydrostatic pressure of the tissue fluid tends to push fluid into capillaries
• the oncotic pressure of the blood tends to pull water back into the blood
• the oncotic pressure of the tissue fluid pulls water into the tissue fluid
• the net result of these forces creates a pressure to push fluid out of the capillary at the arterial end and into the capillary at the venule end

Question 38

What type of muscle is the heart made of?

Answer 38

• cardiac muscles

Question 39

What happens if the coronary arteries had restricted blood flow?

Answer 39

• may cause angina or heart attack (myocardial infarction)

Question 40

Describe the flow of deoxygenated blood in the heart

Answer 40

• deoxygenated blood from the body flows through the vena cava into the right atrium
• blood then flows down the atrio-ventricular valves into the ventricles
• attached to the valves are tendinous cords, which prevents the valves from turning inside out
• deoxygenated blood leaving the right ventricle flows into the pulmonary artery leading to lungs
• at the base of the major arteries, there are semilunar valves to prevent blood returning to the heart as the ventricles relax

Question 41

Describe the flow of oxygenated blood in the heart

Answer 41

• oxygenated blood from lungs flows through the pulmonary vein into the left atrium
• blood flows down through the atriio-ventricular valves into ventricles
• oxygenated blood leaves left ventricle into the aorta, carryinig blood to a number of arteries that supply all parts of the body
• at the base of the major arteries, there are semilunar valves to prevent blood returning to the heart as the ventricles relax

Question 42

Describe and explain how blood pressure affects the structure of the different chambers in the heart

Answer 42

Atria:

• muscle of atrial walls is very thin
• these chambers do not need to create much pressure
• their function is to receive blood from the veins and push it into the ventricles

Right ventricle:

• walls of right ventricle are thicker than walls of atria
• this enables the right ventricle to pump blood out of the heart
• since deoxygenated blood is pumped to the lungs, the blood does not need to travel very far
• also, alveoli in lungs are very delicate, so blood pressure cannot be very high

Left ventricle:

• wall can be two or three times thicker than the right ventricle
• the blood from the left ventricle is pumped out through the aorta and needs sufficient pressure to overcome the resistance of the systemic circulation

Question 43

Describe the structure of cardiac muscle

Answer 43

• consists of fibres that branch, producing cross-bridges
• these help to spread stimulus around the heart and ensures that the muscle can produce a squeezing action rather than a simple reduction in length
• numerous mitochondria between muscle fibrils (myofibrils) to supply energy for contraction
• muscle cells are separated by intercalated discs (thick wavy blue line), which facilitate synchronised contraction
• each cell has a nucleus and is divided into contractile units called sarcomeres (thin blue lines)

Question 44

What is the cardiac cycle?

Answer 44

• the sequence of events in one full beat of the heart

Question 45

Describe the cardiac cycle

Answer 45

• both right and left ventricles pump together
• contraction starts at the apex (base) of the heart so that blood is pushed upwards towards the arteries
• the muscular walls of all four chambers relax
• elastic recoil causes the chambers to increase in volume, allowing blood to flow in from the veins
• both right and left atria contract together
• the muscle in the walls is thin, so only a small pressure is created by this contraction
• this helps to push blood into the ventricles, stretching their walls and ensuring they are full of blood

Question 46

Describe the action of atrio-ventricular valves

Answer 46

• after systole, the ventricular walls relax and recoil:
• the pressure in the ventricles rapidly drops below the pressure in atria
• blood in the atria pushes the atrio-ventricular valves open
• blood entering the heart flows straight through the atria and into the ventricles
• the pressure in the atria and the ventricles rises slowly as they fill with blood
• the valves remain open while the atria contract but close when the atria begin to relax
• this closure is caused by a swirling action in the blood around the valves when the ventricle is full
• as the ventricles begin to contract (systole), the pressure of the blood in the ventricle rises
• when the pressure rises above that in the atria, the blood starts to move upwards
• this movement fills the valve pockets and keeps them closed
• the tendinous cords attached to the valves prevent them from turning inside out
• this prevents blood flowing back into atria

Question 47

Describe the action of the semilunar valves

Answer 47

• before ventricular contraction, the pressure in the major arteries is higher than the pressure in the ventricles
• this means that the semilunar valves are closed
• ventricular systole raises the blood pressure in the ventricles very quickly
• once the pressure in the ventricles rises above the pressure in the major arteries, the semilunar valves are pushed open
• the blood is under very high pressure, so it is forced out of the ventricles in a powerful spurt
• once the ventricle walls have finished contracting, the heart muscle starts to relax (diastole)
• elastic tissue in the walls of the ventricles recoils
• this stretches the muscle out again and returns the ventricle to its original size
• this causes pressure in the ventricles to drop quickly
• as it drops below the pressure in major arteries, the blood starts to flow back towards the ventricles
• the semilunar valves are pushed closed by the blood collecting into the pockets of the valves
• this prevents blood returning to the ventricles
• the pressure wave created when the left semilunar valves close is the pulse that we feel at the neck

Question 48

Describe the graph showing pressure changes in the heart chambers during one cardiac cycle

Answer 48

Question 49

How does the structure of the artery walls play a role in creating even flow of blood?

Answer 49

• the artery walls close to the heart have a lot of elastic tissue
• when blood leaves the heart, these walls stretch
• as blood moves on and out of the aorta, the pressure in the aorta starts to drop
• the elastic recoil of the walls helps to maintain the blood pressure in the aorta
• the further the blood flows along the arteries, the more the pressure drops and fluctuations become less obvious

Question 50

Describe the blood pressure at different parts of the blood system

Answer 50

Question 51

What does ‘the heart muscle is myogenic’ mean?

Answer 51

• it is able to initiate its own contraction, even if not connected to the body

Question 52

What is fibrillation?

Answer 52

• the uncoordinated contraction of the atria and ventricles

Question 53

What is the sino-atrial node?

Answer 53

• a small patch of tissue at the top right atrium, that generates electrical activity
• initiates a wave of excitation at regular intervals
• the pacemaker

Question 54

Describe the contraction of the atria

Answer 54

• the wave of excitation quickly spreads over the walls of both atria
• it travels along the membranes of the muscle tissue
• as the wave of excitation passes, it causes the cardiac muscles to contract
• this is atrial systole
• the tissue at the base of atria cannot conduct a wave of excitation so another node, known as the atrio-ventricular node conducts a wave of excitation through to ventricles
• this wave is delayed allowing atria to finish contracting and for blood to flow into ventricles before they contract

Question 55

Describe the contraction of the ventricles

Answer 55

• after the short delay, the wave of excitation is carried away from the AVN and down specialised conducting tissue called the Purknyne tissue
• this runs down the interventricular septum
• at the base of the septum, the wave of excitation spreads out over the walls of the ventricles
• as the excitation spreads upwards from the base of the ventricles, it causes muscles to contract
• this means that the ventricles contract from the base upwards
• this pushes the blood up towards the major arteries at the top of the heart

Question 56

Label the diagram of the coordination of the cardiac cycle

Answer 56

Question 57

What do P, Q, R, S, T of the ECG show?

Answer 57

• P: excitation of the atria
• QRS: indicates excitation of ventricles
• T: diastole

Question 58

Label diagram of abnormal ECG traces

Answer 58

Question 59

Describe the structure of haemoglobin

Answer 59

• a complex protein with four subunits
• each subunit consists of a polypeptide chain and a haem (non-protein) group
• the haem group consists single iron ion in the form of Fe²⁺
• the iron ion can attract and hold an oxygen molecule
• the haem group is said to have a high affinity for oxygen
• each haemoglobin molecule can carry four oxygen molecules
• there are about 280million molecules of haemoglobin molecules in each red blood cell
• so each red blood cell can carry over a billion oxygen molecules

Question 60

How is oxygen transported?

Answer 60

• oxygen is absorbed into the blood as it passes the alveoli in the lungs
• oxygen molecules diffusing into the blood plasma enter red blood cells
• they become associated with the haemoglobin
• it binds reversibly to haemoglobin
• this takes oxygen molecules out of solution and maintains a steep concentration gradient, allowing more oxygen to enter the blood from lungs and diffuse into cells
• in the body tissues, the oxyhaemoglobin releases the oxygen
• this is dissociation

Question 61

What does the ability of haemoglobin to associated with and release oxygen depend on?

Answer 61

• the concentration of oxygen in the surrounding tissues

Question 62

How is the concentration of oxygen measured?

Answer 62

• it is measured by the relative pressure that is contributes to a mixture of gases
• this is the partial pressure of oxygen or _pO₂
• or oxygen tension, measured in kPa

Question 63

Describe the haemoglobin dissociation curve

Answer 63

• the way that haemoglobin can associate with oxygen produces an S-shaped curve
• at low oxygen tension, haemoglobin does not readily associate with oxygen molecules
• because the haem groups that attract the oxygen are in the centre of the haemoglobin molecule
• this makes it difficult for the oxygen molecule to reach the haem group
• as the oxygen tension rises, the diffusion gradient into the haemoglobin molecule increases
• eventually, one oxygen molecule enter the haemoglobin molecule and associated with one of the haem groups
• this causes a slight change of the haemoglobin molecule, known as conformational change
• it allows more oxygen molecules to enter the haemoglobin molecule and associate with other haem groups relatively easily
• so the curve steepens
• as haemoglobin approaches 100% saturation, the curve levels off

Question 64

How and why is fetal haemoglobin slightly different?

Answer 64

• it has a higher affinity for oxygen than adult haemoglobin
• the haemoglobin dissociation curve is to the left of the adult curve
• this is because fetal haemoglobin must be able to associate with oxygen in an environment where oxygen tension is low enough to make adult haemoglobin release oxygen
• in the placenta, where the oxygen tension is low, fetal haemoglobin will absorb oxygen from the surrounding fluid
• this reduces the oxygen tension even further
• so oxygen diffuses from the mother’s blood into the placenta
• this reduces the oxygen tension within the mother’s blood, making maternal haemoglobin release more oxygen

Question 65

What ways are carbon dioxide transported?

Answer 65

• about 5% is dissolved directly in the plasma
• about 10% is combined directly with haemoglobin to form carbaminohaemoglobin
• about 85% is transported in the form of hydrogencarbonate ions (HCO₃^-)

Question 66

How are hydrogencarbonate ions formed?

Answer 66

• carbon dioxide in the blood plasma diffuses into the red blood cells
• it combines with water to form carbonic acid
• this is catalysed by carbonic anhydrase
• CO₂ + H₂O → H₂CO₂
• this carbonic acid dissociates to release H+ ions and HCO₃^- ions
• H₂CO₃ → HCO₃^- + H⁺

Question 67

What is the chloride shift?

Answer 67

• the hydrogencarbonate ions diffuse out of the red blood cells into the plasma
• the charge inside the red blood cell is maintained by the movement of chloride ions from the plasma into the red blood cell
• this is called the chloride shift

Question 68

How is pH maintained in red blood cells?

Answer 68

• to prevent the build of H⁺ ions, they are taken out of solution by associating with haemoglobin to produce haemoglobinic acid (HHb)
• the haemoglobin is acting as a buffer

Question 69

Describe the Bohr effect

Answer 69

• it describes the effect that an increasing concentration of carbon dioxide has on haemoglobin
• carbon dioxide enters red blood cells forming carbonic acid, which dissociates to release hydrogen ions
• these hydrogen ions affect the pH of the cytoplasm, making it more acidic
• the pH affects the tertiary structure of haemoglobin and reduces the affinity of the haemoglobin for oxygen
• it is unable to hold as much oxygen and oxygen is released from the oxyhaemoglobin to the tissues

Question 70

Where does the Bohr effect occur and what effects does it have?

Answer 70

• there will be more carbon dioxide where there is more respiration
• so, there are more hydrogen ions produced and so oxyhaemoglobin release more oxygen
• when more carbon dioxide is present, the haemoglobin becomes less saturated with oxygen
• this causes the haemoglobin dissociation curve to shift downwards, known as the Bohr shift
• this means more oxygen is released for more aerobic respiration to continue