Chapter 7 - Mass transport Flashcards
Where is haemoglobin found?
Inside red blood cells
What is haemoglobin made from?
Protein
What type of structure does haemoglobin have?
Quaternary
What is the primary structure of haemoglobin?
The sequence of amino acids in the four polypeptide chains
What is the secondary structure of haemoglobin?
Each of the polypeptide chains are made into a helix
How many polypeptide chains are there in haemoglobin?
4
What is the tertiary structure of haemoglobin?
Each polypeptide chain is folded into a precise shape
What is the quaternary structure of haemoglobin?
The four polypeptide chains are linked together. Each polypeptide chain is associated with a haem group (a Fe2+ ion) and so the molecule can carry 4 oxygen molecules
What does a haem group contain?
A ferrous (Fe2+) ion
What is the name of the process of binding with oxygen?
Loading (or associating)
What is the name of the process of haemoglobin releasing oxygen?
Unloading (or dissociating)
Where does association with oxygen take place?
Lungs
Where does dissociation of oxygen take place?
Tissues
What does affinity mean?
Tendency to combine with?
Does haemoglobin have a high or low affinity for oxygen?
High - it combines with it easily but releases it less easily
What does haemoglobin form when it associated with oxygen?
Oxyhaemoglobin
What properties does haemoglobin have that makes it successful at transporting oxygen?
It readily binds to oxygen in the lungs and readily dissociates with oxygen in the tissues
How does haemoglobin obtain its contradicting properties?
Its tertiary structure (and so, therefore, the shape of active site) change under certain conditions, like carbon dioxide concentration
What is partial pressure?
A measure of oxygen concentration
When will oxyhaemoglobin release its oxygen?
When there is a low concentration of oxygen
Why do different haemoglobins have different affinities for oxygen?
The DNA base sequence differs between species. As a result of this, the mRNA and tRNA sequences will be different too. Therefore, the amino acid sequence constructed by the ribosome will be different. Bonds will form in different places and so the tertiary and quaternary structures will be different. This impacts the haemoglobin’s ability to bind to oxygen
What is an oxygen dissociation curve?
It shows how saturated haemoglobin is with oxygen at any given partial pressure
Why is the gradient of the oxygen dissociation curve shallow initially?
At low oxygen concentrations, the haemoglobin has a low affinity for oxygen (so it releases it rather than associating with it). This is because it changes its shape to make it harder for oxygen to bind to it
What happens once the first molecule of oxygen has bonded to the haemoglobin?
The binding of the oxygen molecule makes the haemoglobin change its shape so that is easier for the other haem groups to bind to an oxygen molecule
Why does the gradient of the oxygen dissociation curve steepen?
Once the first molecule of oxygen has bound to the haemoglobin, it only takes a small increase in partial pressure to bind the second molecule. This is an example of positive cooperativity (binding the first makes the second easier and so on)
Why does the gradient of the oxygen dissociation curve level out?
Probability - three of the binding sites are occupied so the probability of an oxygen molecule binding with the fourth is small
What does an oxygen dissociation curve that is further to the left show?
The greater the affinity for oxygen (loads easily, unloads with difficulty)
What does an oxygen dissociation curve that is further to the right show?
The lower the affinity for oxygen (loads with difficulty, unloads easily)
Why does a mouse’s haemoglobin have a lower affinity for oxygen?
It has a high surface area to volume ratio so loses heat easily. This means it must have a high metabolic rate (and therefore require lots of aerobic respiration to create energy)
Why might the affinity of haemoglobin of a carp be higher than that of a mackerel?
The carp is found in deep, freshwater lakes where there isn’t much oxygen, whereas the mackerel lives at the surface of the lake where there is lots of oxygen
What is the Bohr effect?
When cells respire, they release CO2
This reduces the partial pressure of oxygen
This increases the rate of oxygen unloading and so the dissociation curve shifts to the right. More CO2 is released
Why would the oxygen dissociation curve at the lungs be shifted to the left?
The concentration of CO2 is low because it is excreted from the lungs. The affinity of haemoglobin increases because of the high concentration of oxygen in the lungs, shifting the curve to the left
Why would the dissociation curve for the muscles be shifted to the right?
The concentration of CO2 is high because of the increased levels of respiration. The affinity of haemoglobin and the concentration of oxygen is lower, which means oxygen is easily unloaded into muscle cells, shifting the curve to the right
Why does carbon dioxide change the shape of a haemoglobin molecule?
Dissolved CO2 is acidic and the low pH changes the shape of haemoglobin by breaking bonds
How does pH influence the affinity of haemoglobin?
In the lungs, CO2 is constantly removed. This raises the pH, which changes the shape of haemoglobin into one that loads oxygen easily and has a high affinity for it, so it isn’t released on the way to respiring tissues. In these tissues, respiring cells produce carbon dioxide. This lowers the pH and changes the shape of the haemoglobin into one that has a lower affinity for oxygen and releases it more easily. Oxygen is released into the tissues
Why is more oxygen released from haemoglobin in cells with a fast rate of respiration?
More CO2 = lower pH = greater the haemoglobin shape change = more readily oxygen is unloaded
Why do lugworms’ haemoglobin have a high affinity for oxygen?
Lugworms live in burrows in the sand. They get their oxygen from the fresh seawater that washes over them in the burrow. When the tide goes out, however, the concentration of oxygen in the remaining water is very low. The affinity of its haemoglobin must be very high to extract as much of this oxygen as possible
Why does the haemoglobin of llamas have a high affinity for oxygen?
It lives at high altitudes where the partial pressure of oxygen is much lower. Therefore, its haemoglobin must be able to extract as much oxygen as possible
What is important to remember about haemoglobin releasing oxygen?
In normal circumstances, only one oxygen molecule will be released. However, when the partial pressure of oxygen is very low, 3 molecules may be. Either way, the haemoglobin still contains some oxygen when it travels back to the lungs
Why is a mass transport system needed?
Mammals have a low surface area to volume ratio, so simple diffusion isn’t effective at moving large quantities of materials over large distances
What is the mass transport in mammals?
The circulatory system
What is the circulatory system made up of?
The heart and blood vessels
What is the function of the heart?
It pumps blood through the blood vessels to reach different parts of the body
What is the function of the blood?
Transports respiratory gases, products of digestion, metabolic waste and hormones around the body
What are the two paths blood can take in the circulation system?
One loop takes blood from the heart to the lungs, then back to the heart
One loop takes blood around the rest of the body and back
What blood vessels supply blood to the heart?
Coronary arteries
Why is the transport system essential? (2)
It must absorb nutrients and respiratory gases and excrete products
Takes materials from cells to the exchange surface and from the exchange surface to cells
What two factors decide whether a specialist transport system is needed?
The surface area to volume ratio
How active the organism is
What four characteristics must a successful exchange system have?
A suitable medium in which to carry materials
A form of mass transport which is more rapid than diffusion
A closed system of tubular vessels
A mechanism for moving the transport medium between vessels
Why are transport mediums mainly water based?
Water readily dissolves substances and can be moved around easily
How is the mechanism for moving the transport medium between vessels achieved?
Maintaining a pressure difference
What are the two ways in which a successful transport system is achieved?
Animals use a muscular contraction (can be heart or other muscles)
Plants rely on natural, passive processes like the evaporation of water
What three important mechanisms must be present in the circulatory system?
A way to stop backflow (e.g. valves)
A way of controlling the flow of the medium which suits the changing needs of different body parts
A mechanism for the mass transport of gases or water
What does the phrase ‘closed, double circulatory system’ mean?
The blood is confined to blood vessels and passes through the heart twice for each complete circuit of the body
Why does blood not go directly from the lungs to the tissues that require it?
In the lungs, the pressure of the blood is very low. If this was to travel around the body, the rate of circulation would be too slow. Returning the blood to the heart increases its pressure and so it reaches the tissues of the body faster
Why is it important that blood reaches the tissues that need it quickly?
Mammals have a high body temperature and so high metabolism
What does the left-hand pump of the heart deal with?
Oxygenated blood from the lungs
What does the right-hand side pump of the heart deal with?
Deoxygenated blood from the body
What are the two chambers found in each pump?
The atrium and the ventricle
Characteristics of the atrium
Thin-walled and elastic and stretches to collect blood
Characteristics of the ventricle
Thick muscular wall to pump blood long distances
Why is it important that the heart has two separate pumps?
The blood has to pass through the tiny capillaries in the lungs, which vastly reduces the pressure. This means that the flow of blood to the rest of the body would be very slow
Why does the right ventricle have a thinner muscular wall?
It only pumps blood to the lungs
Why does the left ventricle have a thicker muscular wall?
It pumps blood around the body
What are the two valves found in the heart?
The left atrioventricular (bicuspid) valve
The right atrioventricular (tricuspid) valve
Why do ventricles have thicker walls than the atria?
They have to push blood a longer distance
What is important to remember about the two sides of the heart?
They pump in time
What is the job of the coronary arteries?
To supply the heart with oxygen
What happens when the coronary arteries get blocked?
Myocardial infarction (heart attack)
Why does a heart attack occur?
An area of the heart is deprived of oxygen. This means that the cells can’t respire aerobically and die
When will a valve open?
When there is high pressure behind them
Why is too much salt bad?
It increases blood pressure
Why is too much saturated fat bad?
It increases cholesterol
What are the two types of molecule found in cholesterol?
High-density lipoproteins
Low-density lipoproteins
What do high-density lipoproteins do?
Remove cholesterol from arteries and transport it to the liver for excretion
What do low-density lipoproteins do?
Transport cholesterol from the liver to body tissues
Why is having a high blood pressure bad?
High blood pressure means that the arteries are more likely to have an aneurysm (burst) and cause a haemorrhage
Why is carbon monoxide bad?
It binds easily to haemoglobin to form carboxyhaemoglobin, which reduces the oxygen-carrying capacity of the blood. The heart then works faster to supply oxygen to the tissues
Why is nicotine bad?
Stimulates the production of adrenaline which makes the heart work faster = high blood pressure
Characteristics of the aorta?
Connected to the left ventricle and carries oxygenated blood o the body
Characteristics of the vena cava?
Connected to the right atrium and brings deoxygenated blood back to the heart
Characteristics of the pulmonary vein
Connected to the left atrium and brings oxygenated blood back from the lungs
Characteristics of the pulmonary artery
Connected to the right ventricle and carries deoxygenated blood to the lungs
What is cardiac output?
The volume of blood pumped by one ventricle in one minute
How do you calculate cardiac output?
Heart rate x stroke volume
What happens to ventricular pressure as the heart beats?
It starts low, but as the atria contract, the ventricles fill with blood and pressure increases. When the left atrioventricular valves close, the pressure increases dramatically as the muscular walls of the ventricle contract. When this pressure is higher than the pressure in the aorta, the semilunar valves between the two open and blood flows into the atria, lowering the pressure in the ventricles.
What happens to atrial pressure as the heart beats?
It’s always relatively low because the thin atria walls can’t create much force. It increases when the muscles contract, but then falls as the left ventricular valves close and the muscles relax. The pressure increases as the atria fill with blood and the drops as the blood flows into the ventricles
What happens to aortic pressure as the heart beats?
It increases as blood is forced into the aorta from the ventricles. It then falls, but the elasticity of its wall creates a recoil action which stops it dropping very low
What happens to ventricular volume as the heart beats?
It rises as the atria contract and fill the ventricles with blood, then drops as the semilunar valves open and blood is forced out of the aorta
What is the function of arteries?
Carry blood from the heart into the arterioles
What is systole?
Contraction of the heart
What is diastole?
Relaxing of the heart
What happens when the heart relaxes?
Blood returns to the atria via the vena cava and the pulmonary vein. This massively increases the pressure in the atria until it overtakes the pressure of the ventricles, pushing blood into them when the atrioventricular valves open. When the pressure in the ventricles is lower than that in the aorta and pulmonary artery, the semilunar valves close.
What happens when the atria contract?
The remaining blood in the atria is forced into the ventricles because the volume is decreased, so pressure increases
What happens when the ventricles contract?
Once the ventricles fill with blood, their walls contract. This increases the pressure within them, forcing the atrioventricular valves to close. Once the pressure in the ventricles exceeds that of the aorta and pulmonary artery, blood is forced into them.
What are valves used for?
To prevent blood flowing in the wrong direction
When will a valve open?
When the pressure behind them is greater than the pressure in front
Where are atrioventricular valves located?
Between the atria and ventricles
When do atrioventricular valves prevent blood flow?
When the ventricles contract and their pressure exceeds the pressure of the atria
Where are semilunar valves located?
In the aorta and pulmonary artery
When do semilunar valves have to prevent backflow?
When the pressure in the pulmonary artery and aorta exceeds that of the ventricles when the ventricle walls contract
What is a closed circulatory system?
Blood is confined to blood vessels so the pressure can be regulated
Where are pocket valves located?
Throughout the body in veins
When do pocket valves prevent backflow?
When the skeletal muscles contract, increasing the pressure of the veins, blood must flow towards the heart, not away from it
What is the structure of these valves?
Deep bowls of fibrous but flexible tissue. When the pressure is greater on the concave side than the convex, blood collects within the bowl of the cusps. This pushes them together to form a tight fit that prevents the flow of blood
What are arteries?
Vessels that carry the blood from the heart into arterioles
What are arterioles?
Small vessels that control the flow of blood from arteries to capillaries
What are capillaries?
Vessels that arterioles to veins
What are veins?
Vessels that carry blood from capillaries to the heart
What is the function of the tough, fibrous layer?
It resists both internal and external pressure changes
What is the function of the muscular layer?
It contracts to help blood flow
What is the function of the elastic layer?
It can recoil to maintain a constant blood pressure
What is the function of the endothelium?
It is smooth (reduces friction) and thin (easy diffusion)
What is the function of the lumen?
The cavity through which blood flows
Why do arteries have a thick muscular layer?
Small arteries can constrict and dilate to control the passage of blood through them
Why do arteries have a thick elastic layer?
It maintains blood pressure so blood can reach extremities by stretching and recoiling
Why do arteries have such thick walls?
To stop the vessel bursting under high pressure
Why are there no valves in arteries?
The blood is under such high pressure it tends to only flow in one direction
Why do arterioles have a thicker muscle layer than arteries?
This allows the lumen to constrict, restricting the flow of blood into capillaries
Why do arterioles have a thinner elastic layer than arteries?
The blood pressure is lower
Why do veins only need a thin muscle layer?
Veins carry blood away from tissues so can’t restrict the flow of blood to the tissues
Why do veins only need a thin elastic layer and a thinner outer wall?
The blood is at a much lower pressure
Why do veins have valves?
Because the blood is at such a low pressure, there is the risk of the blood flowing in the wrong direction
Why do capillaries have such thin walls?
Small diffusion pathway
Why are capillaries highly branched and numerous?
Higher surface area for exchange
Why do capillaries have such a small diameter?
So they can permeate between tissues, meaning a cell is never far from a capillary
Why is the lumen of capillaries small?
So red blood cells are squashed against the lining, meaning the diffusion pathway is even smaller
Why are there gaps between the endothelium cells?
White blood cells can escape to deal with infections in tissues
What does tissue fluid do?
It supplies tissues with substances like glucose, ions and oxygen
What is hydrostatic pressure?
Pressure created by the heart pumping
What is translocation?
The movement of solutes to where they are needed in a plant
Where does translocation take place?
Phloem
What is the source of a solute?
Where it is made
What is the sink of a solute?
The area where it is used up
What is the name of the current theory of translocation?
The mass flow theory
How is a concentration gradient maintained in the sinks?
Enzymes break down the solute into something else
How does translocation work?
Sucrose is created in the chloroplasts
Sucrose diffuses down a concentration gradient by facilitated diffusion into companion cells
Active transport moves hydrogen ions into the spaces within the cell walls of companion cells
Sucrose is co-transported with the hydrogen ions and they move down a concentration gradient into the sieve tubes
The sieve tubes now have a more negative water potential
Because the xylem has a less negative water potential, water moves into the phloem, creating high hydrostatic pressure
At the sinks, solutes are removed and used up
Sucrose is actively transported into the sinks from the sieve tubes, resulting in a lower water potential
Water moves into these cells by osmosis from sieve tubes
This creates low hydrostatic pressure in the sieve tubes
This creates a pressure gradient from source to sink, so water and therefore sucrose moves down the concentration gradient
Why is translocation an active process?
It all starts with the active transport of hydrogen ions
Evidence for the mass flow hypothesis (4)
Companion cells have many mitochondria = lots of ATP
If the sucrose concentration in leaves increases, the concentration of sucrose in sinks increases too
Sap is produced when sieve tubes are cut, showing there is pressure within them
When metabolic processes are inhibited, translocation stops
Evidence against the mass flow hypothesis
Not all solutes move at the same speed
The function of sieve plates are unclear - surely they should hinder translocation?
Sucrose is delivered to all regions at the same rate
What is transpiration?
Evaporation of water from the leaves
How would you estimate transpiration rate?
Cut a shoot diagonally underwater
Keeping the shoot underwater, assemble the potometer
Check the apparatus is watertight
Shut the tap on the potometer
Remove the capillary tube from the water and allow one air bubble to form
Record the starting distance of the air bubble and use a stopwatch to measure its movements
Why does water evaporate from the leaves when stomata are open?
The atmosphere is normally less humid than the air next to the stomata. This means there is a water potential gradient and so water molecules diffuse into the surrounding air.
How does water move between the cells of the leaf?
The air spaces in the leaf get heated by the sun, so they have a much lower water potential. Water moves from mesophyll cells to the air spaces, lowering the mesophyll cell’s water potential. Water enters the mesophyll cells by osmosis from neighbouring cells. This chain continues, creating a water potential gradient
What is the cohesion-tension theory?
Water evaporates from mesophyll cells due to evaporation and transpiration
Water molecules are cohesive- they form hydrogen bonds with each other and tend to stick together
Water forms a continuous, unbroken column across mesophyll cells and down the xylem
As more transpiration occurs, more water molecules are dragged along after each other to replace water lost
This creates a transpiration pull - a column of water moving up the xylem
Transpiration is pulling water up and gravity is pulling it down. This is the cohesion-tension theory
Evidence supporting the cohesion-tension theory (3)
When transpiration is at its greatest, there are more forces pulling the xylem inwards, which reduces the diameter of a tree trunk
If a xylem vessel is broken, air interrupts the unbroken stream of water, meaning the tree can’t draw up water
When a xylem vessel is broken, water doesn’t leak out because of the pressure. Instead, air is drawn in
Why is it important that xylem cells are dead?
They have no cell walls so form a continuous tube through which water can move
How would you use a ringing experiment to investigate transport in the phloem and xylem?
Remove a section of the protective layer and phloem from around the plant
After some time, you should see that the stem immediately above the section where the phloem was removed begins to swell
Sugars in the phloem accumulate above the cut region, causing it to swell, whilst the tissues below this region die due to the interruption of sugars
What do the results of the ringing experiment suggest?
Phloem are the vessels responsible for transporting sugars in plants
Evidence that transportation of sugars occurs in the phloem (3)
When phloem are cut, organic molecules flow out
Plants provided with radioactive carbon dioxide present traces of radioactive carbon in phloem after a short time
Removing a ring of phloem from the steam results in the accumulation of sugars above the ring and the loss of sugars below the ring
How can you use radioactive isotopes to prove it is phloem that transport sugars?
Radioactive carbon dioxide is supplied to the plant
This radioactive substance will be incorporated into the products of photosynthesis
Autoradiography can then be used to follow the path of these products as they move around the plant
To do this, the plant is killed. Cross sections of the stem are placed onto film and wherever the film turns black, the radioactive substance is present
The blackened regions correspond to where phloem are in the stem
What is an atheroma and how does it form?
If the endothelium is damaged, WBCs and lipids clump together to form fatty areas
Over time, these form a fibrous plaque called an atheroma
This restricts blood flow, so increases blood pressure and increases the risk of coronary heart disease
What is an aneurysm?
Atheromas damage and weaken arteries. When blood travels through a weakened area, it can push the inner layers through the outer layers, forming a balloon-like swelling, which can burst and form a haemorrhage
What is thrombosis?
The atheroma bursts the endothelium, leaving a rough surface on the artery wall
Platelets accumulate here and can cause a blood clot
How does cholesterol increase the risk of heart disease?
Fatty deposits can form atheromas, leading to myocardial infarction (a heart attack)
Why can high blood pressure increase the risk of heart disease?
It increases the risk of damage to artery walls, and so the chances of atheromas. These can form blood clots and lead to heart attacks
What is hydrostatic pressure?
The pressure created by the heart beating
How is tissue fluid formed?
At the arterial end of a capillary, the hydrostatic pressure is much higher than the pressure in the existing tissue fluid. This means fluids are forced out of capillaries and into the spaces around cells, forming more tissue fluid
What are the two forces resisting the formation of tissue fluid?
The hydrostatic pressure of the existing tissue fluid, which resists the movement of water into it
The lower water potential of the blood, which causes fluid to move back into capillaries
What is ultrafiltration?
Pressure at the arterial end of capillaries pushes small molecules from the capillaries and leaves only cells and large molecules like proteins in the blood
How does tissue fluid return to the circulatory system?
Most tissue fluid returns via the capillaries
Loss of fluid from capillaries reduces the hydrostatic pressure inside them
When the blood reaches the venous end of the capillary, it’s pressure is normally lower than the pressure of the surrounding tissue fluid
Tissue fluid is forced back into capillaries because of the higher hydrostatic pressure outside them
The capillaries also have a lower water potential than the surrounding tissue fluid, so water moves from the tissues into capillaries by osmosis
What happens to excess tissue fluid?
It is drained into the lymphatic system, where it goes to lymph nodes to deal with infections. It then re-enters the circulatory system at the jugular vein
How are fluids in the lymphatic system transported?
The hydrostatic pressure of the tissue fluid that has left capillaries
Contraction of body muscles
