Pack 8 - Mass Transport Flashcards
Describe the primary structure of haemoglobin?
Sequence of amino acids
Describe the secondary structure of haemoglobin?
Polypeptide chains are cooked into an α helix
Describe the tertiary structure of haemoglobin?
Each polypeptide chain is folded into a precise shape.
Describe the quaternary structure of haemoglobin?
Four polypeptide chains are linked to form an almost spherical molecule. Each chain is associated with a ham group which contains Fe²⁺.
How many O₂ molecules can one haemoglobin molecule combine with and why?
4 as there are 4 harm groups in one haemoglobin molecule.
Give two names for the process by which O₂ binds to haemoglobin.
Loading/associating.
Give two names for the process by which O₂ is released from haemoglobin.
Unloading/dissociating
Where does loading/association of O₂ to haemoglobin occur in humans?
In the capillaries of the lungs.
Where does unloading/dissociation of O₂ from haemoglobin occur in humans?
The capillaries in respiring tissues.
What is the difference between a haemoglobin molecule with a ‘high affinity for oxygen’ anda haemoglobin molecule with a ‘low affinity for oxygen’?
- A haemoglobin molecule with a ‘high affinity for oxygen’ takes up oxygen more easily but release it less easily.
- A haemoglobin molecule with a ‘low affinity for oxygen’ takes up oxygen less easily but release it more easily.
What is the role of haemoglobin?
To transport oxygen.
“to be efficient at transporting oxygen, haemoglobin must…” - Complete the statement (2 points) in terms of where oxygen is unloaded and is loaded.
- …readily associate with O₂ at the gas exchange surface.
* …readily dissociate from O₂ at the tissues requiring O₂.
Why is it important haemoglobin can change its infinity for O₂?
So it can readily associate with O₂ at the gas exchange surface.
AND so it readily dissociate from O₂ at the tissues requiring O₂.
Why does haemoglobin’s affinity for oxygen change at respiring tissues compared with in the lungs?
Haemoglobin changes its shape in the presence of CO₂ so that O₂ binds more loosely. There is a high conc. of CO₂ in the respiring tissues.
Why does haemoglobin need a low affinity for O₂ at respiring tissues?
So that O₂ is unloaded.
Do all organisms possess the same type of haemoglobin molecule?
No.
Why do different haemoglobin molecules have different affinities for O₂
They have slightly difference sequence of animo acids and therefore slightly different tertiary and quaternary structure.
Describe and explain the initial shape of an ODC (1st O₂).
- Increases slowly.
- Due to the shape of haemoglobin, it is difficult for the first O₂ to bind. Therefore at low O₂ PP, little O₂ binds so curve is shallow.
Define Partial pressure of a gas.
Concentration of a given gas in air
What does the term ‘positive cooperativity’ mean in terms of oxygen binding to Hb.
The affinity of haemoglobin for O₂ is increased by the binding of O₂ molecules.
Describe and explain the middle part of the shape of an ODC (2nd/3rd O₂).
- The binding of the first O₂ molecule changes the quaternary structure of haemoglobin, making it easier for the other harm groups to bind to O₂.
- Therefore a smaller increase in O₂ PP is required for the 2nd O₂ to bind than the 1st.
- Gradient steepens
Describe and explain the final part of the shape of an ODC (4th O₂).
For the 4th O₂ molecule however, although in theory it is easier for the molecule to bind, the curve flattens due to the probability of O₂ coming in contact with the ahem group being reduced due to the other 3 haem groups being occupied.
Fill in the gaps twice:
'’The further to the ____ the ODC, the _______ the affinity of haemoglobin for oxygen.”
left, lower, greater, right
- Left + Greater
* Right + Lower
How does the concentration fo CO₂ affect haemoglobin’s affinity for O₂? What is the name for this effect?
- The greater the concentration of CO₂, the lower the affinity go haemoglobin for O₂.
- Bohr effect
Explain how CO₂ conc. in the lungs affects haemoglobin.
- Conc. of CO₂ is low.
- Haemoglobin affinity for O₂ is therefore increased.
- O₂ is readily loaded.
Explain how CO₂ conc. in respiring tissues affects haemoglobin.
- Conc. of CO₂ is high.
- Haemoglobin affinity for O₂ is therefore decreased.
- O₂ is readily unloaded.
Give two reasons oxygen is readily unloaded from Hb in respiring tissues.
- High CO₂ conc. decreases Hb affinity for O₂.
* Low O₂ PP
Which way does a high CO₂ conc. shift the ODC?
Right
Why does a high CO₂ conc. decrease haemoglobin’s infinity for O₂?
Dissolved CO₂ is acidic so it changes the shape of haemoglobin.
Describe how an increased activity of a tissue increases the amount of O₂ unloaded.
- Higher respiration rate
- More CO₂ produced
- Lower pH
- Greater shape change of Hb
- O₂ unloaded more readily
Why do different species have different haemoglobins?
They have evolved adaptations to their environment and conditions.
Will a llama’s haemoglobin have a higher or lower affinity for oxygen than humans living at sea level?
Higher as they live at altitude so the air has a lower PP.
Do animals that live in environments with a low oxygen PP have a ODC to the left or right?
Left as they need a higher affinity for O₂ so Hb is saturated even in low oxygen concentrations.
Do animals such as birds and fast swimming fish have a ODC to the left or right? Explain why
Right - • High metabolic rate • More respiration • Hb has lower affinity for oxygen. • O₂ is unloaded more readily.
Would a mouse have an ODC to the left or right of humans? Explain why?
Right - they are smaller so have a larger SA to volume ratio. Therefore they lose heat rapidly. Therefore they need to respire more to maintain their body heat so need more oxygen. So therefore oxygen is unloaded more easily.
What two factors determine whether an organism needs a specialised transport medium and whether it is transported by a pump?
- small SA:V ratio
* high activity
Give 7 common features of an efficient mass transport system.
- A suitable medium - e.g. blood (water readily dissolves substances)
- A form of mass transport to quickly transport in bulk over large distances - e.g. heart
- A closed system of tubular vessels that contain the medium and reach all parts of the organism - e.g. blood vessels
- A mechanism for moving the medium within the vessels. Requires pressure differences.
- Maintain flow in one direction - e.g. valves
- A means of controlling the flow to suit the changing needs of different parts of the organism.
- A mechanism for the mass flow of water or gases. - e.g. lungs/breathing
How do most animals move mass transport medium?
Contraction of a specialised pump (heart) OR body muscle contraction
How do plants move mass transport medium?
Passive processes such as evaporation of water.
Why do mammals have a double circulatory system?
When blood is passed through the lungs its pressure is reduced. Therefore it is returned to the heart to increase its pressure before being circulated to the rest of the body tissue so it is delivered quickly.
Describe the journey of blood starting in the aorta.
Aorta -> arteries/arterioles -> capillaries -> veins/veinules -> vena cava -> right atrium -> right ventricle -> pulmonary artery -> lungs -> pulmonary vein -> left atrium -> left ventricle -> aorta
How does the contents of the blood get from capillaries into body cells?
Diffusion
Which have thicker walls the atria or the ventricles?
Ventricles
Which has a thicker wall the left ventricle or the right ventricles?
The left
Why is it important there is no mixing of blood between the left and right side of the heart?
To maintain the pressures of each chamber.
What is the name of the valves between the atria and the ventricles?
- Left atrioventricular (bicuspid) valve
* Right atrioventricular (tricuspid) valve
What is the name of the arteries that supply the heart muscle with oxygen?
• Coronary arteries
What does a blockage of the coronary arteries lead to?
Myocardial infarction (heart attack)
Does the pulmonary artery carry oxygenated blood?
No - deoxygenated
Does the pulmonary vein carry oxygenated blood?
yes
Give 4 risk factors of heart disease.
- Smoking
- High blood pressure
- High salt/saturated fat diet
- High levels of low-density lipoproteins
Explain how two chemicals found in cigarettes increase the chance of heart disease.
- Carbon monoxide - combines permanently with haemoglobin - reduces oxygen delivered to body cells - heart has to work harder - raised blood pressure.
- Nicotine - stimulates adrenaline - increases heart rate and raises blood pressure.
Describe three ways in which high blood pressure can lead to heart disease.
- Heart must work harder to pump blood - may fail.
- More likely to develop aneurysm (weakening of artery wall) and burst.
- to resist pressure artery walls thicken restricting blood flow.
Explain how low density lipoproteins can lead to heart disease.
- LDL transport cholesterol from the liver to tissues including artery walls
- Can lead to the development if an atheroma (fatty deposit in arteries)
- Lead to heart disease
Why can high salt diet lead to heart disease?
• Raises blood pressure
Why can high saturated fat diet lead to heart disease?
Increases LDL levels and therefore blood cholesterol concentration.
What does systole mean?
Contraction
What does diastole mean?
Relaxation
What are the three stages of the cardiac cycle (in order)?
- diastole
- atrial systole
- ventricular systole
When do the atrioventricular valves open?
When the pressure of the atria exceeds the pressure in the ventricles.
During diastole are the semilunar valves closed and why?
Yes, when the pressure of the ventricles is lower than that of the aorta and pulmonary artery.
Describe what happens during diastole.
- Blood enters atria.
- When atrial pressure is greater than the ventricular pressure the atrioventricular valves open.
- Blood moves into the ventricles and their walls recoil
Describe what happens during the atrial systole.
- Contraction of atrial walls
- recoil of ventricular walls
- remaining blood is forced into the ventricles
During atrial systole which chambers are relaxed?
Atria contract
Ventricles relax.
Describe what happens during the ventricular systole.
- atria relax
- ventricles contract
- ventricular pressure increases
- atrioventricular valves shut
- Pressure rises further
- When pressure in ventricles is greater than in aorta and pulmonary artery, the semi lunar valves open.
- Blood is forced out.
From where do the ventricles start contracting and why?
The bottom to keep the blood moving upwards.
When does the left semi lunar valves close?
When the pressure in the aorta is greater than the pressure in the left ventricle.
What is the purpose of valves in the circulatory system.
To prevent back flow of blood.
Blood will always flow from an area of high to low pressure. How does the circulatory system ensure blood flows in the right direction when the desired direction of flow is to a lower pressure?
Valves
Name three types of valves in the circulatory system.
- Atrioventricular
- Semi-lunar
Where are the atrioventricular valves found?
Between the atria and the ventricles
Where are the pocket valves found?
In veins
Where are the semi-lunar valves found?
Between the aorta and the left ventricle
AND between the pulmonary artery and the right ventricle.
What is the role of the semi-lunar valves?
To prevent back flow of blood from the aorta and pulmonary artery into the ventricles during diastole and atrial systole when the pressure in these arteries is greater than the relaxed ventricles.
What is the role of the atrioventricular valves?
- They prevent back flow of blood from the ventricles to the atria.
- This occurs when the ventricles contracts meaning their pressures are greater than those of the atria.
- It ensures blood flows into the arteries and not the atria when ventricles contract.
Briefly describe the shape of the valves and how this prevents back flow.
Made up of cusps. On the convex side when pressure is greater they open. On the concave side when pressure is greater blood collects in the ‘bowls’ and closes them.
What is the advantage of a closed circulatory system like that found in mammals.
Pressures can be controlled and maintained.
Define cardiac output; give an equation and the units.
The volume of blood pumped by one ventricle of the heart in a minute.
Cardiac output = heart rate x stroke volume (volume pumped out in each beat)
units: dm³min⁻¹
List the blood vessels in order.
- Arteries
- Arterioles
- Capillaries
- Veinules
- Veins
What is the role of the arterioles?
To control blood flow from arteries to capillaries.
From the outside in, list the layers of arteries and veins.
- Tough fibrosis outer layer
- Muscle layer
- Elastic layer
- Thin inner lining
- Lumen
From the outside in, list the layers of arteries and veins.
- Tough fibrosis outer layer
- Muscle layer
- Elastic layer
- Thin inner lining
- Lumen
What is the role of the tough fibrosis outer layer of arteries and veins?
Resists pressure changes inside and out
What is the role of the muscle layer of arteries and veins?
Can contract to control blood flow
What is the role of the elastic layer of arteries and veins?
Helps maintain blood pressure by stretching and recoiling.
What is the role of the thin inner lining of arteries and veins?
Smooth to reduce friction/thin to allow diffusion
Is the muscle layer of arteries thicker or thinner than veins? Why?
Thicker - so smaller arteries can contract and dilate in order to control blood flow.
Is the elastic layer in arteries thicker or thinner than in veins? Why?
Thicker - It is important that blood pressure is kept high in arteries so blood reaches the extremities of the body. The elastic wall stretches and recoils with each beat of the heart. This maintains the high pressure and smoothes pressure surges created by the ventricular systole.
Why is the overall wall thickness of the arteries greater than that of the veins?
To resist bursting under high pressures.
Do arteries have valves? Why (not)?
No (except aorta and pulmonary artery) - blood is under high pressure therefore no back flow.
Is the muscle layer of arterioles relatively thinner thicker than arteries? Why?
Thicker - The contraction of this muscle layer restricts blood flow and controls movement of blood into capillaries.
Is the elastic layer of arterioles relatively thinner thicker than arteries? Why?
Thinner - because blood pressure is lower.
Is the muscle layer of veins thicker or thinner than arteries? Why?
thinner - no need to control blood flow.
Is the elastic layer of veins thicker or thinner than arteries? Why?
Thinner - low pressure means veins will not burst and pressure is too low to create recoil.
Is the overall thickness of veins walls thicker or thinner than arteries? Why?
Thinner - pressure is too low for a risk of bursting. Allows them to be flattened easily.
Explain how pocket valves work.
When body muscles contract, veins are compressed. This pressures blood within them. Valves ensure that this pressure directs blood in one direction towards the heart.
Describe the structure of a capillary.
One cell thick wall. Narrow lumen
Why is the capillary wall one cell thick.
Short diffusion distance allowing rapid diffusion of materials between the blood and cells.
Why is the capillary lumen very narrow?
RBC are squeezed through decreasing their speed and increasing time for diffusion. They are against the capillary walls so this decreases diffusion distance.
What is one advantage of capillaries having a narrow diameter? (Not to do with RBC)
They can permeate tissues meaning no cell is far away from a capillary. Short diffusion distance.
What is the advantage of capillaries being highly branched and numerous?
Large surface area for exchange. No cell is far away.
Why are there gaps in the endothelial lining of capillaries?
to allow WBC to escape and deal with infection.
What medium do cells live in?
Tissue fluid
What medium are substances directly exchanged into from cells in between the blood?
Tissue fluid
What is tissue fluid formed from?
Blood plasma
What force causes tissue fluid to move out of the arterial end of the capillaries?
Hydrostatic pressure
Which two forces oppose the hydrostatic pressure of the blood plasma in the arterial end of the capillaries?
- Hydrostatic pressure of the tissue fluid outside the capillaries. (acts on liquid)
- Lower water potential of the blood which causes water to move back into the plasma by osmosis.
What does hydrostatic pressure act upon compared to what osmosis acts upon?
Osmosis - water
Hydrostatic pressure - the liquid.
In which direction is the overall pressure in the arterial end of the capillaries?
Outwards - from the plasma to the tissue fluid.
Why is the water potential in the capillaries lower than the tissue fluid?
It contains plasma proteins and larger molecules that don’t leave the plasma.
What is ultrafiltration of blood plasma during tissue formation?
Hydrostatic pressure is only large enough to force small molecules out of the capillaries leaving cells and proteins in the blood.
Explain why tissue fluid moves back into the capillaries at the venous end of the capillaries.
- Loss of fluid from the capillaries means the hydrostatic pressure is lower in the capillaries than in the tissue fluid.
- Therefore tissue fluid is forced into the capillaries.
- In addition, the plasma has lost water so the water potential is lower than in the tissue fluid.
- Therefore water leaves the tissue fluid by osmosis.
What happens to excess tissue fluid that is not returned to the capillaries?
It moves into the lymphatic system through lymph vessels.
What eventually happens to tissue fluid in the lymphatic system?
It drains back into the veins near the heart via two ducts.
Give two ways in which the contents of the lymphatic system is moved.
- Hydrostatic pressure of the tissue fluid
* contraction of body muscles that squeeze lymph vessels.
List the two routes by which tissue fluid returns to the blood stream.
- Reabsorption into capillaries
* Drainage into lymphatic system.
What is the name of the vessels that water moves through in a plant?
Xylem
Describe how water moves out of the stomata in plants?
- Water potential is lower outside the stomata than in the air spaces so water moves out down a water potential gradient.
- This water is replaced by water evaporation from the cell walls of surrounding mesophyll cells.
How can plants control their rate of transpiration?
Opening and closing stomata.
Describe how water moves from the xylem vessels to the sub stomatal air spaces? (cytoplasmic route)
- mesophyll cells lose their water to the air spaces by evaporation.
- these cells now have a lower water potential so water enters from neighbouring cells by osmosis.
- water loss from these cells lowers their water potential
- they in turn take in water from their neighbours by osmosis.
Describe how cohesion-tension theory suggests water moves up the stem.
- Water molecules form hydrogen bonds between one another and stick together - cohesion.
- Water forms a continuous, unbroken column across the mesophyll cells and down the xylem.
- As water evaporates from the mesophyll cells, water molecules are drawn up behind it as a result.
- A column of water is therefore pulled up the xylem.
What is transpiration pull?
The movement of water being pulled up the xylem due to the evaporation of water form the mesophyll layer and the cohesion-tension.
Give three pieces of evidence for the cohesion-tension theory.
- During the day when transpiration is at its greatest plants steam diameter shrink due to increased tension in the xylem pulling the vessels inwards.
- If a xylem vessel is broken and air enters, the plant can no longer draw up water since the continuous column of water is broken.
- When a xylem vessel is broken, water does not leak out. Instead air is drawn in since it is under tension.
Why is transpiration passive?
Does not require energy as it relies on evaporation due to the sun.
What is transpiration?
The evaporation of water form the leaves.
Transpiration is hard to measure what can instead by measure and how does this equate to the rate of transpiration? What equipment is used?
- rate of water uptake as 99% of water uptake is lost through transpiration.
- potometer
What is translocation?
The process by which organic molecules and some mineral ions are transported from one part of a plant to another.
What are phloem made up of?
Sieve tube elements.
Describe the structure of sieve tube elements.
- Long and thin
- Arranged end to end
- Sieve plates have pores
What cells surround sieve tube elements?
Companion cells.
What is the site of production of sugars from photosynthesis known as?
Source
What is the place in a plant where sugars will be directly used or stored called?
Sinks
In which direction do molecules in the phloem flow? Why?
Both directions - sinks can be above or below sources.
What organic molecules does the phloem transport? What inorganic ions does the phloem transport?
- Sucrose
- Amino acids
- Potassium, chloride, phosphate, magnesium
What is the mass flow theory? (briefly)
the mechanism by which molecules are moved by translocation
Explain in 4 steps how sucrose is moved into the sieve elements from photosynthesising tissue.
- Sucrose in manufactured from products of photosynthesis in cells with chloroplasts.
- Sucrose diffuses down a concentration gradient by facilitated diffusion from photosynthesising cells into companion cells.
- H+ ions are actively transported from companion cells into the spaces within cell walls using ATP.
- These H+ ions diffuse down a concentration gradient through carrier proteins into the sieve tube elements.
- Sucrose molecules are transported along with H+ ions - co-transport.
Describe in 8 steps the process of mass flow of sucrose through sieve tubes.
- Sucrose produced by source cells is actively transported into the sieve tubes.
- This causes the sieve tubes to have a lower water potential.
- Xylem has a much higher ψ so water moves from xylem into the sieve tubes by osmosis. This creates a high hydrostatic pressure inside the sieve tubes.
- At the sink cells, sucrose is used in respiration up or converted to starch.
- These cells therefore have a low sucrose content so sucrose is actively transported in to hem lowering their ψ.
- Due to this lowered ψ, water also moves into the sink cells by osmosis.
- Hydrostatic pressure of sieve tubes near sink cells is therefore reduced.
- Therefore due to high HP at the source sieve tubes and a low HP at the sink sieve tubes, there is a mass flow of sucrose solution down this HP gradient.
Give 6 pieces of evidence supporting the mass flow hypothesis.
- there is pressure within the sieve tubes as shown by sap being released when stems are cut.
- concentration of sucrose is higher in leaves (source) than roots (sink)
- downward flow in the phloem occurs in the phloem during daylight but ceases in darkness.
- increases in sucrose levels in the leaf are followed by similar increases in the phloem a little later.
- metabolic poisons inhibit translocation of sucrose.
- companion cells possess many mitochondria.
Give 3 pieces of evidence against the mass flow hypothesis.
- The function of sieve plates is unclear, as they seem to hinder mass flow (may be structural)
- Not all solutes move at the same speed, they should do with mass flow.
- Sucrose is delivered more or less at the same rate to regions, rather than quicker to those with the lowest sucrose concentrations.
How is sucrose transported from the sieve tube elements into storage or other sink cells?
Sucrose is actively transported by companion cells out of the sieve tubes and into the sink cells.
