transport in animals

Question 1

the need for a circulatory system

Answer 1

The cells of all living organisms need a constant supply of reactants for metabolism, e.g. oxygen and glucose

These materials are gained from the environment via exchange surfaces

Single celled organisms can gain oxygen and glucose directly across their surface membranes and the molecules can diffuse to all parts of the cell quickly due to short diffusion distances

Larger organisms gain these reactants via specialised exchange surfaces, but because they are made up of many layers of cells, the time taken for substances such as glucose and oxygen to diffuse to every cell in the body would be far too long

The diffusion distances involved are too great
To solve this problem their exchange surfaces are connected to a mass transport system, for example

The digestive system is connected to the circulatory system

The lungs are connected to the circulatory system
Circulatory systems are systems that transport fluids containing oxygen, nutrients and waste

Question 2

single and double circulatory system

Answer 2

There are two different models of circulatory systems, single circulatory systems and double circulatory systems

In a single circulatory system, the blood passes through the heart once during one complete circuit of the body

In a double circulatory system, the blood passes through the heart twice during one complete circuit of the body

Fish have a single circulatory system while mammals have a double circulatory system

Question 3

single circulatory system in fish

Answer 3

Deoxygenated blood is pumped to the gills from the heart

The gills are the exchange site where oxygen and carbon dioxide are exchanged with the atmosphere and the blood

The oxygenated blood flows from the gills to the rest of the body

It travels through the capillaries in organs, delivering oxygen and nutrients
The blood returns to the heart
The heart only has one atrium and one ventricle

Question 4

double circulatory system in mammals

Answer 4

In mammals the blood passes throught the heart twice during a single circuit of the body

As a result the mammalian heart has a left side and right side with a wall (septum) dividing the two
The left side contains oxygenated blood and the right side contains deoxygenated blood
Blood in the right side of the heart leaves and travels to the lungs

The blood returns to the left side of the heart before being pumped around the rest of the body
Once the blood has passed through all the other organs and tissues it returns to the right side of the heart

In general, any blood that has just passed through an organ goes straight back to the heart, not to another organ
The hepatic portal vein is the exception to this rule, it allows blood from the gut to flow to the liver

Question 5

advantages of double circulation

Answer 5

It is believed that a double circulatory system has evolved from the single circulatory system as there are several benefits to a double circulatory system
When blood enters a capillary network the pressure and speed drops significantly

In a single circulatory system, the blood has to pass through two capillary networks before returning to the heart

In a double circulatory system, the blood only passes through one capillary network before returning to the heart

As a result, the double circulation maintains higher blood pressure and average speed of flow
This increased pressure and speed helps to maintain a steeper concentration gradient which allows for the efficient exchange of nutrients and waste with the surrounding tissues

Question 6

open and closed circulatory system

Answer 6

Circulatory systems are either open or closed
In a closed circulatory system, blood is pumped around the body and is always contained within a network of blood vessels

All vertebrates and many invertebrates have closed circulatory systems
In an open circulatory system, blood is not contained within blood vessels but is pumped directly into body cavities

Organisms such as arthropods and molluscs have open circulatory systems.

Humans have a closed double circulatory system: in one complete circuit of the body blood passes through the heart (the pump) twice

The right side of the heart pumps blood deoxygenated blood to the lungs for gas exchange; this is the pulmonary circulatory system
Blood then returns to the left side of the heart, so that oxygenated blood can be pumped efficiently (at high pressure) around the body; this is the systemic circulatory system

Question 7

circulatory system in insects

Answer 7

Insects have one main blood vessel - the dorsal vessel

The tubular heart in the abdomen pumps haemolymph (this is what blood in insects is called) into the dorsal vessel

The dorsal vessel delivers the haemolymph into the haemocoel (body cavity)

Haemolymph surrounds the organs and eventually reenters the heart via one-way valves called ostia

Unlike the blood in a mammals circulatory system, the haemolymph is not specifically directed towards any organs in an insect

Insects are able to survive with this less efficient circulatory system because oxygen is delivered directly to their tissues via tracheae (a system of tubes) that connect directly to the outside

Question 8

arteries, arterioles, veins and venues

Answer 8

The body contains several different types of blood vessel:
Arteries: transport blood away from the heart (usually at high pressure) to tissues

Arterioles: arteries branch into narrower blood vessels called arterioles which transport blood into capillaries

Veins: transport blood to the heart (usually at low pressure)

Venules: these narrower blood vessels transport blood from the capillaries to the veins

Blood flows through the lumen of a blood vessel; the size of the lumen varies depending on the type of blood vessel (with arteries having a narrow lumen, and the veins a wider one)

The walls of each type of blood vessel have a structure that relates to the function of the vessel. Arteries, arterioles, veins & venules all have varying structural features

Question 9

structure of arteries

Answer 9

Artery walls consist of three layers: tunica adventitia/externa, tunica media and tunica intima

The tunica intima is made up of an endothelial layer, a layer of connective tissue and a layer of elastic fibres

The endothelium is one cell thick and lines the lumen of all blood vessels. It is very smooth and reduces friction for free blood flow

The tunica media is made up of smooth muscle cells and a thick layer of elastic tissue
Arteries have a thick tunica media

The layer of muscle cells strengthen the arteries so they can withstand high pressure. It also enables them to contract and narrow the lumen for reduced blood flow

The elastic tissue helps to maintain blood pressure in the arteries. It stretches and recoils to even out any fluctuations in pressure

The tunica adventitia covers the exterior of the artery and is mostly made up of collagen
Collagen is a strong protein protects blood vessels from damage by over-stretching

Arteries have a narrow lumen which helps to maintain a high blood pressure
A pulse is present in arteries

Question 10

structure of arterioles

Answer 10

Arterioles possess a muscular layer that means they can contract and partially cut off blood flow to specific organs
Eg. During exercise blood flow to the stomach and intestine is reduced which allows for more blood to reach the muscles

Unlike arteries, arterioles have a lower proportion of elastic fibres and a large number of muscle cells
The presence of muscle cells allows them to contract and close their lumen to stop and regulate blood flow

Question 11

structure of veins

Answer 11

Veins return blood to the heart
They receive blood that has passed through capillary networks (blood pressure is very low and it must be returned to the heart)

The tunica media is much thinner in veins
There is no need for a thick muscular layer as veins don’t have to withstand high pressure

The lumen of the vein is much larger than that of an artery
A larger lumen helps to ensure that blood returns to the heart at an adequate speed
A large lumen reduces friction between the blood and the endothelial layer of the vein
The rate of blood flow is slower in veins but a larger lumen means the volume of blood delivered per unit of time is equal

Veins contain valves
These prevent the backflow of blood, helping return blood to the heart
A pulse is absent in veins

Question 12

structure of venues

Answer 12

Venules connect the capillaries to the veins
They have few or no elastic fibres and a large lumen
As the blood is at low pressure after passing through the capillaries there is no need for a muscular layer

Question 13

capillaries

Answer 13

Capillaries are a type of blood vessel present in the circulatory system
They have thin walls which are “leaky”, allowing substances to leave the blood to reach the body’s tissues
They can form networks called capillary beds which are very important exchange surfaces within the circulatory system

Question 14

structure and function of capillaries

Answer 14

Capillaries have a very small diameter (lumen)
This forces the blood to travel slowly which provides more opportunity for diffusion to occur

A large number of capillaries branch between cells
Substances can diffuse between the blood and cells quickly as there is a short diffusion distance
The wall of the capillary is made solely from a single layer of endothelial cells (this layer also lines the lumen in arteries and veins)

The wall is only one cell thick – this reduces the diffusion distance for oxygen and carbon dioxide between the blood and the tissues of the body
The cells of the wall have gaps called pores which allow blood plasma to leak out and form tissue fluid

White blood cells can combat infection in affected tissues by squeezing through the intercellular junctions in the capillary walls

Question 15

formation of tissue fluid

Answer 15

Plasma is a straw-coloured liquid that constitutes around 55 % of the blood
Plasma is largely composed of water (95 %) and because water is a good solvent many substances can dissolve in it, allowing them to be transported around the body

As blood passes through capillaries some plasma leaks out through gaps in the walls of the capillary to surround the cells of the body
This results in the formation of tissue fluid

The composition of plasma and tissue fluid are very similar, although tissue fluid contains far fewer proteins
Proteins are too large to fit through gaps in the capillary walls and so remain in the blood

Tissue fluid bathes almost all the cells of the body that are outside the circulatory system
Exchange of substances between cells and the blood occurs via the tissue fluid
For example, carbon dioxide produced in aerobic respiration will leave a cell, dissolve into the tissue fluid surrounding it, and then move into the capillary

Question 16

tissue fluid formation

Answer 16

The volume of liquid that leaves the plasma to form tissue fluid depends on two opposing forces

Hydrostatic pressure
This is the pressure exerted by a fluid, e.g. blood
The hydrostatic pressure in this example is the blood pressure, generated by the contraction of the heart muscle

Oncotic pressure
This is the osmotic pressure exerted by plasma proteins within a blood vessel
Plasma proteins lower the water potential within the blood vessel, causing water to move into the blood vessel by osmosis

Question 17

at the arterial end

Answer 17

When blood is at the arterial end of a capillary the hydrostatic pressure is great enough to force fluid out of the capillary

Proteins remain in the blood as they are too large to pass through the pores in the capillary wall

The increased protein content creates a water potential gradient (osmotic pressure) between the capillary and the tissue fluid

At the arterial end the hydrostatic pressure is greater than the osmotic pressure so the net movement of water is out of the capillaries into the tissue fluid

Question 18

at venous end

Answer 18

At the venous end of the capillary the hydrostatic pressure within the capillary is reduced due to increased distance from the heart and the slowing of blood flow as it passes through the capillaries

The water potential gradient between the capillary and the tissue fluid remains the same as at the arterial end

At the venous end the osmotic pressure is greater than the hydrostatic pressure and water begins to flow back into the capillary from the tissue fluid

Roughly 90 % of the fluid lost at the arterial end of the capillary is reabsorbed at the venous end

The other 10 % remains as tissue fluid and is eventually collected by lymph vessels and returned to the circulatory system

If blood pressure is high (hypertension) then the pressure at the arterial end is even greater

This pushes more fluid out of the capillary and fluid begins to accumulate around the tissues. This is called oedema

Question 19

formation of lymph

Answer 19

Some tissue fluid reenters the capillaries while some enters the lymph vessels
The lymph vessels are separate from the circulatory system

They have closed ends and large pores that allow large molecules to pass through
Larger molecules that are not able to pass through the capillary wall enter the lymphatic system as lymph
Small valves in the vessel walls are the entry point to the lymphatic system

The liquid moves along the larger vessels of this system by compression caused by body movement. Any backflow is prevented by valves
This is why people who have been sedentary on planes can experience swollen lower limbs

The lymph eventually reenters the bloodstream through veins located close to the heart
Any plasma proteins that have escaped from the blood are returned to the blood via the lymph capillaries

If plasma proteins were not removed from tissue fluid they could lower the water potential (of the tissue fluid) and prevent the reabsorption of water into the blood in the capillaries

After digestion lipids are transported from the intestines to the bloodstream by the lymph system

Question 20

heart structure

Answer 20

The human heart has a mass of around 300g and is roughly the size of a closed fist
The heart is a hollow, muscular organ located in the chest cavity

it is made up of cardiac muscle, it does not get fatigued and need to rest unlike skeletal muscle. the coronary arteries supply the cardiac muscle with oxygenated blood. the heart is surrounded by inelastic pericardial membranes which help prevent the heart from over distending with blood

It is protected in the chest cavity by the pericardium, a tough and fibrous sac

The heart is divided into four chambers. The two top chambers are atria and the bottom two chambers are ventricles

The left and right sides of the heart are separated by a wall of muscular tissue, called the septum. The portion of the septum which separates the left and right atria is called the interatrial septum, while the portion of the septum which separates the left and right ventricles is called the interventricular septum

The septum is very important for ensuring blood doesn’t mix between the left and right sides of the heart

Question 21

valves in the heart

Answer 21

Valves in the heart:
Open when the pressure of blood behind them is greater than the pressure in front of them

Close when the pressure of blood in front of them is greater than the pressure behind them

Valves are important for keeping blood flowing forward in the right direction and stopping it flowing backwards.

They are also important for maintaining the correct pressure in the chambers of the heart

The right atrium and right ventricle are separated by the atrioventricular valve, which is otherwise known as the tricuspid valve

The right ventricle and the pulmonary artery are separated by the pulmonary valve

The left atrium and left ventricle are separated by the mitral valve, which is otherwise known as the bicuspid valve

The left ventricle and aorta are separated by the aortic valve
There are two blood vessels bringing blood to the heart; the vena cava and pulmonary vein

There are two blood vessels taking blood away from the heart; the pulmonary artery and aorta

Question 22

coronary arteries

Answer 22

The heart is a muscle and so requires its own blood supply for aerobic respiration

The heart receives blood through arteries on its surface, called coronary arteries

It’s important that these arteries remain clear of plaques, as this could lead to angina or a heart attack (myocardial infarction)

Question 23

cardiac cycle

Answer 23

The contraction of the heart is called systole, while the relaxation of the heart is called diastole

in diastole the heart relaxes and the atria and the the ventricles fill with blood, the volume and pressure of the blood builds as the heart fills but the pressure in the arteries is at a minimum

in systole the atria contract (atrial systole) closely followed by the ventricles (ventricular systole). the pressure inside the heart increases dramatically and blood is forced out of the right side of the heart to the lungs and from the left side to the main body circulation. volume and pressure are low at the end of systole.

Atrial systole is the period when the atria are contracting and ventricular systole is when the ventricles are contracting

During ventricular systole, blood is forced out of the pulmonary artery (to the lungs) and aorta (to the rest of the body)

One systole and diastole makes a heartbeat and lasts around 0.8 seconds in humans. This is the cardiac cycle

Question 24

pressure changes

Answer 24

During systole and diastole, heart valves open and close as a result of pressure changes

Valves are an important mechanism to stop blood flowing backwards

During diastole, the heart is relaxing

The atrioventricular valves open and the semilunar valves are closed

During systole, the heart contracts and pushes blood out of the heart

During this time, the atrioventricular valves are closed and the semilunar valves are open

Question 25

the cardiac cycle

Answer 25

A cardiac cycle is the sequence of events that make up a single heartbeat
It includes periods of heart muscle contraction and relaxation

One cardiac cycle is followed by another in a continuous process

There is no gap between cycles where blood stops flowing
The contraction of the muscles in the wall of the heart reduces the volume of the heart chambers and increases the pressure of the blood within that chamber

When the pressure within a chamber/vessel exceeds that in the next chamber/vessel the valves are forced open and the blood moves through

When the muscles in the wall of the heart relax they recoil which increases the volume of the chamber/vessel and decreases the pressure so that the valves close

Question 26

analysis the cardiac cycle

Answer 26

The curves on the graph represent the pressure of the left atria, aorta and the left ventricle

The points at which the curves cross each other are important because they indicate when valves open and close

Point A - both left atrium and left ventricle are relaxed
Pressure sits at roughly 0 kPa
Between points A and B - atrial systole
Left atria contracts and empties blood into the left ventricle

Point B - beginning of the ventricular systole
Left ventricular pressure increases
AV valve shuts
Pressure in the left atria drops as the left atrium expands

Point C - pressure in the left ventricle exceeds that in the aorta
Aortic valve opens
Blood enters the aorta

Point D - diastole
Left ventricle has been emptied of blood
Muscles in the walls of the left ventricle relax and pressure falls below that in aorta
Aortic valve closes
AV valve opens

Point E - expansion of the left ventricle
There is a short period of time during which the left ventricle expands
This increases the internal volume of the left ventricle which decreases the pressure

Question 27

cardiac output

Answer 27

Cardiac output (CO) is the term used to describe the volume of blood that is pumped by the heart (the left and right ventricle) per unit of time

An average adult has a cardiac output of roughly 4.7 litres of blood per minute when at rest
Individuals who are fitter often have higher cardiac outputs due to having thicker and stronger ventricular muscles in their hearts

Cardiac output increases when an individual is exercising
This is so that the blood supply can match the increased metabolic demands of the cells

Question 28

how can the co of an individual be calculated

Answer 28

The CO of an individual can be calculated using their heart rate and stroke volume
Heart rate is the number of times a heart beats per minute
This can also be described as the number of cardiac cycles per minute

Stroke volume is the volume of blood pumped out of the left ventricle during one cardiac cycle

Question 29

calculating cardiac output

Answer 29

Cardiac output is found by multiplying the heart rate by the stroke volume:
Cardiac output = heart rate x stroke volume

The equation can be rearranged to find the heart rate and stroke volume if required
Heart rate = cardiac output ÷ stroke volume
Stroke volume = cardiac output ÷ heart rate

Question 30

the need for transport systems in animals

Answer 30

All living organisms have the need to exchange substances with their surrounding environment

They need to take oxygen and nutrients in
Waste products generated need to be released

The location within an organism where this occurs is described as an exchange site
E.g. lungs in humans (gases) and roots in plants (water and minerals)

Substances are said to not have entered or left an organism until it crosses the cell surface membrane

Small organisms like the single-celled Chlamydomonas are able to exchange substances directly with the environment
This is due to their large surface area: volume ratio

The diffusion or transport distance in these organisms are very small so essential nutrients or molecules are able to reach the necessary parts of the cell efficiently

Smaller organisms also tend to have lower levels of activity and so smaller metabolic demands

Question 31

increasing transport distances in larger animals

Answer 31

In larger, more complex organisms (both plants and animals) the important exchange sites tend to be far away from the other cells within the organism

This large transport distance makes simple diffusion a non-viable method for transporting substances all the way from the exchange site to the rest of the organism

Diffusion wouldn’t be fast enough to meet the metabolic requirements of cells

Question 32

surface area:volume ratio

Answer 32

Surface area and volume are both very important factors in the exchange of materials in organisms

The surface area refers to the total area of the organism that is exposed to the external environment

The volume refers to the total internal volume of the organism (total amount of space inside the organism)

As the surface area and volume of an organism increase (and therefore the overall ‘size’ of the organism increases), the surface area: volume ratio decreases

This is because volume increases much more rapidly than surface area as size increases

Single-celled organisms have a high SA: V ratio which allows for the exchange of substances to occur via simple diffusion

The large surface area allows for maximum absorption of nutrients and gases and secretion of waste products

The small volume means the diffusion distance to all organelles is short

Question 33

what happens to the sa:v ratio as the size of the organism increases

Answer 33

As organisms increase in size their SA: V ratio decreases

There is less surface area for the absorption of nutrients and gases and secretion of waste products

In addition, the greater volume results in a longer diffusion distance to the cells and tissues of the organism

Question 34

increasing levels of activity

Answer 34

Larger organisms are not only more physically active but they also contain more cells than smaller organisms

A larger number of cells results in a higher level of metabolic activity

As a result, the demand for oxygen and nutrients is greater and more waste is produced

The increased demand for oxygen and nutrients along with the greater need for the disposal of waste means that diffusion is not an efficient transport mechanism for larger organisms

Question 35

what are mass transport systems

Answer 35

Larger organisms have evolved specialised mass flow transport systems that enable the efficient transport of nutrients and waste

Mass flow is the bulk movement of materials. It is directed movement so involves some sort of force

In mass transport systems there is still some diffusion involved but only at specific exchange sites at the start and end of the route travelled by the substances
The lungs are the exchange site of the gas exchange system

Question 36

what does mass transport help with

Answer 36

Bring substances quickly from one exchange site to another

Maintain the diffusion gradients at exchange sites and between cells and their fluid surroundings

Ensure effective cell activity by keeping the immediate fluid environment of cells within a suitable metabolic range

Question 37

the heart beat

Answer 37

Control of the basic heartbeat is myogenic, which means the heart will beat without any external stimulus

This intrinsic rhythm means the heart beats at around 60 times per minute

Question 38

control of the heart action

Answer 38

The sinoatrial node (SAN) is a group of cells in the wall of the right atrium. The SAN initiates a wave of depolarisation that causes the atria to contract

The Annulus fibrosus is a region of non-conducting tissue which prevents the depolarisation spreading straight to the ventricles

Instead, the depolarisation is carried to the atrioventricular node (AVN)
This is a region of conducting tissue between atria and ventricles

After a slight delay, the AVN is stimulated and passes the stimulation along the bundle of His
This delay means that the ventricles contract after the atria

The bundle of His is a collection of conducting tissue in the septum (middle) of the heart.

The bundle of His divides into two conducting fibres, called Purkyne tissue, and carries the wave of excitation along them
The Purkyne fibres spread around the ventricles and initiate the depolarization of the ventricles from the apex (bottom) of the heart

This makes the ventricles contract and blood is forced out of the pulmonary artery and aorta

Question 39

electrocardiographs (ECGs)

Answer 39

Electrocardiography can be used to monitor and investigate the electrical activity of the heart

Electrodes that are capable of detecting electric signals are placed on the skin
These electrodes produce an electrocardiogram (ECG)

An ECG shows a number of distinctive electrical waves produced by the activity of the heart

A healthy heart produces a distinctive shape in an ECG

Question 40

the p wave

Answer 40

Caused by the depolarisation of the atria, which results in atrial contraction (systole)

Question 41

theQRS complex

Answer 41

Caused by the depolarisation of the ventricles, which results in ventricular contraction (systole)

This is the largest wave because the ventricles have the largest muscle mass

Question 42

the T wave

Answer 42

Caused by the repolarisation of the ventricles, which results in ventricular relaxation (diastole)

Question 43

the u wave

Answer 43

Scientists are still uncertain of the cause of the U wave, some think it is caused by the repolarisation of the Purkyne fibres

Question 44

tachycardia

Answer 44

When the heart beats too fast it is tachycardic
An individual with a resting heart rate of over 100 bpm is said to have tachycardia

Question 45

bradycardia

Answer 45

When the heart beats too slow it is bradycardic
An individual with a resting heart rate below 60 bpm is said to have bradycardia
A lot of fit individuals or athletes tend to have lower heart rates and it is usually not dangerous

Question 46

ectopic heart beat

Answer 46

This condition is caused by an early heartbeat followed by a pause
It is common in the population and usually requires no treatment unless very severe

Question 47

fibrillation

Answer 47

An irregular heartbeat will disrupt the rhythm of the heart
Severe cases of fibrillation can be very dangerous, even fatal

Question 48

transport of oxygen

Answer 48

The majority of oxygen transported around the body is bound to the protein haemoglobin in red blood cells

Red blood cells are also known as erythrocytes

Each molecule of haemoglobin contains four haem groups, each able to bond with one molecule of oxygen

This means that each molecule of haemoglobin can carry four oxygen molecules, or eight oxygen atoms in total

haemoglobins have postive co operativity- as one oxygen binds to a haem group, the molecule changes shape making it easier for the next oxygen molecules to bind

Question 49

formation of oxyhaemoglobin

Answer 49

When oxygen binds to haemoglobin, oxyhaemoglobin is formed

Oxygen + Haemoglobin = Oxyhaemoglobin

4O2 + Hb= Hb4O 2

The binding of the first oxygen molecule results in a conformational change in the structure of the haemoglobin molecule, making it easier for each successive oxygen molecule to bind; this is COOPERATIVE binding

The reverse of this process happens when oxygen dissociates in the tissues

Question 50

carbon dioxide transport

Answer 50

Waste carbon dioxide produced during respiration diffuses from the tissues into the blood

There are three main ways in which carbon dioxide is transported around the body

A very small percentage of carbon dioxide dissolves directly in the blood plasma and is transported in solution

Carbon dioxide can bind to haemoglobin, forming carbaminohaemoglobin

A much larger percentage of carbon dioxide is transported in the form of hydrogen carbonate ions (HCO3-)

Question 51

formation of hydrogen carbonate ions

Answer 51

Carbon dioxide diffuses from the plasma into red blood cells
Inside red blood cells carbon dioxide combines with water to form hydrogen carbonate ions and hydrogen ions
CO2 + H2O ⇌ H2CO3 + h+

Question 52

the role of carbonic anahydrase in the formation of HC ions

Answer 52

Red blood cells cytoplasm contains the enzyme carbonic anhydrase which catalyses the reaction between carbon dioxide and water

Without carbonic anhydrase this reaction proceeds very slowly

The plasma contains very little carbonic anhydrase hence H2CO3 forms more slowly in plasma than in the cytoplasm of red blood cells

Carbonic acid dissociates readily into H+ and HCO3- ions
H2CO3 ⇌ HCO3– + H+

Question 53

role haemoglobinic acid in the formation of HC ions

Answer 53

Hydrogen ions can combine with haemoglobin, forming haemoglobinic acid and preventing the H+ ions from lowering the pH of the red blood cell

Haemoglobin is said to act as a buffer in this situation

The hydrogen carbonate ions diffuse out of the red blood cell into the blood plasma where they are transported in solution

prevents changes in the pH by accepting free hydrogen ions in a reversible reaction to form haemoglobinic acid

Question 54

the chloride shift

Answer 54

carbonic a hydrate catalyses the reversible reaction between co2 and h2o to form carbonic acid. the carbonic acid then dissociates to form hydrogen carbonate ions and h+ ions. the negatively charged hydrogen carbonate ions move out of the erythrocytes into the plasma by diffusion down a conc gradient and negatively charged chloride ions move into the erythrocytes, which maintains the electrical balance of the cell- chloride shift.

The chloride shift is the movement of chloride ions into red blood cells that occurs when hydrogen carbonate ions are formed

Hydrogen carbobate ions are formed by the following process

Carbon dioxide diffuses into red blood cells
The enzyme carbonic anhydrase catalyses the combining of carbon dioxide and water to form carbonic acid (H2CO3)
CO2 + H2O ⇌ H2CO3

Carbonic acid dissociates to form hydrogen carbonate ions and hydrogen ions
H2CO3 ⇌ HCO3- + H+

Question 55

chloride shift (negatively charged)

Answer 55

Negatively charged hydrogencarbonate ions formed from the dissociation of carbonic acid are transported out of red blood cells via a transport protein in the membrane

To prevent an electrical imbalance, negatively charged chloride ions are transported into the red blood cells via the same transport protein

If this did not occur then red blood cells would become positively charged as a result of a buildup of hydrogen ions formed from the dissociation of carbonic acid

Question 56

the oxygen dissociation curve

Answer 56

The oxygen dissociation curve shows the rate at which oxygen associates, and also dissociates, with haemoglobin at different partial pressures of oxygen (pO2)

Partial pressure of oxygen refers to the pressure exerted by oxygen within a mixture of gases; it is a measure of oxygen concentration

Haemoglobin is referred to as being saturated when all of its oxygen binding sites are taken up with oxygen; so when it contains four oxygen molecules

Question 57

affinity of oxygen

Answer 57

The ease with which haemoglobin binds and dissociates with oxygen can be described as its affinity for oxygen

When haemoglobin has a high affinity it binds easily and dissociates slowly

When haemoglobin has a low affinity for oxygen it binds slowly and dissociates easily

In other liquids, such as water, we would expect oxygen to becomes associated with water, or to dissolve, at a constant rate, providing a straight line on a graph, but with haemoglobin oxygen binds at different rates as the pO2 changes; hence the resulting curve

It can be said that haemoglobin’s affinity for oxygen changes at different partial pressures of oxygen

Question 58

explaining the shape of the oxygen dissociation curve

Answer 58

The curved shape of the oxygen dissociation curve for haemoglobin can be explained as follows

Due to the shape of the haemoglobin molecule it is difficult for the first oxygen molecule to bind to haemoglobin; this means that binding of the first oxygen occurs slowly, explaining the relatively shallow curve at the bottom left corner of the graph

After the first oxygen molecule binds to haemoglobin, the haemoglobin protein changes shape, or conformation, making it easier for the next haemoglobin molecules to bind; this speeds up binding of the remaining oxygen molecules and explains the steeper part of the curve in the middle of the graph

The shape change of haemoglobin leading to easier oxygen binding is known as cooperative binding

As the haemoglobin molecule approaches saturation it takes longer for the fourth oxygen molecule to bind due to the shortage of remaining binding sites, explaining the levelling off of the curve in the top right corner of the graph

Question 59

interpreting the oxygen dissociation curve

Answer 59

When the curve is read from left to right, it provides information about the rate at which haemoglobin binds to oxygen at different partial pressures of oxygen

Question 60

at low po2 in the curve

Answer 60

At low pO2, in the bottom left corner of the graph, oxygen binds slowly to haemoglobin; this means that haemoglobin cannot pick up oxygen and become saturated as blood passes through the body’s oxygen-depleted tissues
Haemoglobin has a low affinity for oxygen at low pO2, so saturation percentage is low

Question 61

at medium po2 in the curve

Answer 61

At medium pO2, in the central region of the graph, oxygen binds more easily to haemoglobin and saturation increases quickly; at this point on the graph a small increase in pO2 causes a large increase in haemoglobin saturation

Question 62

at high po2 in the curve

Answer 62

At high pO2, in the top right corner of the graph, oxygen binds easily to haemoglobin; this means that haemoglobin can pick up oxygen and become saturated as blood passes through the lungs

Haemoglobin has a high affinity for oxygen at high pO2, so saturation percentage is high

Note that at this point on the graph increasing the pO2 by a large amount only has a small effect on the percentage saturation of haemoglobin; this is because most oxygen binding sites on haemoglobin are already occupied

Question 63

when the dissociation curve is read from right to left analysis

Answer 63

When read from right to left, the curve provides information about the rate at which haemoglobin dissociates with oxygen at different partial pressures of oxygen

In the lungs, where pO2 is high, there is very little dissociation of oxygen from haemoglobin

At medium pO2, oxygen dissociates readily from haemoglobin, as shown by the steep region of the curve; this region corresponds with the partial pressures of oxygen present in the respiring tissues of the body, so ready release of oxygen is important for cellular respiration

At this point on the graph a small decrease in pO2 causes a large decrease in percentage saturation of haemoglobin, leading to easy release of plenty of oxygen to the cells

At low pO2 dissociation slows again; there are few oxygen molecules left on the binding sites, and the release of the final oxygen molecule becomes more difficult, in a similar way to the slow binding of the first oxygen molecule

Question 64

foetal haemoglobin

Answer 64

The haemoglobin of a developing foetus has a higher affinity for oxygen than adult haemoglobin- if the baby had the same affinity as the mother little or no oxygen would be transferred

This is vital as it allows a foetus to obtain oxygen from its mother’s blood at the placenta- the mothers oxygenated blood runs close to the deoxygenated fetal blood

Fetal haemoglobin can bind to oxygen at low pO2

At this low pO2 the mother’s haemoglobin is dissociating with oxygen

On a dissociation curve graph, the curve for foetal heamoglobin shifts to the left of that for adult haemoglobin

This means that at any given partial pressure of oxygen, foetal haemoglobin has a higher percentage saturation than adult haemoglobin

After birth, a baby begins to produce adult haemoglobin which gradually replaces foetal haemoglobin

This is important for the easy release of oxygen in the respiring tissues of a more metabolically active individual

Question 65

different types of haemoglobin

Answer 65

Haemoglobin is a quaternary protein, made up of four globin polypeptides and four haem groups

The structure of haem is identical in all types of haemoglobin

The globin chains however can differ substantially between species

The globin polypeptides determine the precise properties of haemoglobin
There are a wide range of haemoglobin types that exist

They vary in their oxygen-binding properties
They bind to and release oxygen in different conditions

Environmental factors can have a major impact on the evolution of haemoglobin within a species

Question 66

effects of altitude

Answer 66

The partial pressure of oxygen is lower at higher altitudes

Species living at high altitudes have haemoglobin that is adapted to these conditions

For example, llamas have haemoglobin that binds very readily to oxygen

This is beneficial as it allows them to obtain a sufficient level of oxygen saturation in their blood when the partial pressure of oxygen in the air is low

Question 67

bohr shift

Answer 67

as the partial pressure of carbon dioxide rises (higher partial pressure of co2) haemoglobin gives up oxygen more easily. this change is known as the bohr effect

• in active tissues with a high partial pressure of co2, haemoglobin gives up its oxygen more readily
  -in the lungs where the proportion of co2 in the air is relatively low, oxygen binds to the haemoglobin molecules easily

Question 68

transporting carbon dioxide

Answer 68

5% carried dissolves into plasma
10-20% is combined with the amino groups in the polypeptide chains of haemoglobin to form a compound called carbaminohaemoglobin
75-85% is converted into hydrogen carbonate ions (HCO3-) in the cytoplasm of the red blood cells.

Question 69

hole in heart

Answer 69

the development of the septum is not completed until after birth, in the foetus the blood is oxygenated in the placenta not in the lungs so all the blood in the heart is similar and mixes freely. in the days after the birth the gap in the septum must close to keep oxygenated blood and deoxygenated blood completely separate. a hole in the heart can be heard as a heart murmur with a stethoscope