✅7 - Mass Transport Flashcards
What is associating?
When haemoglobin binds with oxygen
Where does loading take place?
In the lungs
What is dissociating?
When haemoglobin releases its oxygen
Where does unloading take place?
The tissues
Haemoglobins with a high affinity for oxygen…
…take it up easily but release it less easily
Haemoglobins with a low affinity for oxygen…
…don’t take it up easily but release it easily
What is the role of haemoglobin?
To transport oxygen
What features must haemoglobin have to be efficient at transporting oxygen?
Readily dissociate with oxygen at the surface where gas exchange occurs
Readily dissociate from oxygen at the tissues requiring it
When does haemoglobin change affinity?
Under different conditions, such as O2 and CO2 concentrations
Why do different haemoglobins have different affinities for oxygen?
Because they have different shapes as each species produces a different amino acid sequence so the tertiary and quaternary structure are different
What is an oxygen dissociation curve?
The graph of the relationship between the saturation of haemoglobin and oxygen partial pressure
At low oxygen concentrations, why does little oxygen bind to haemoglobin?
Because the shape of the haemoglobin molecule makes it difficult for the first oxygen molecule to bind to one of the sites on its four polypeptide subunits because they are closely united
Why is it easier for the second oxygen molecule to bind to haemoglobin?
Because the binding of the first oxygen molecule changes the quaternary structure of the haemoglobin and makes it easier for other subunits to bind to an oxygen molecule
What is positive cooperativity?
Binding the first molecule makes binding of the second easier and so on
What happens after the binding of the third oxygen molecule?
It is harder to bind the fourth, as the majority of the binding sites are filled and it is less likely that a single oxygen molecule will find an empty site to bind to
What is the shape of the oxygen dissociation curve?
Sigmoidal
The further the curve is to the left…
…the greater the affinity of haemoglobin for oxygen
The further the curve is to the right…
…the lower the affinity of haemoglobin for oxygen
How does haemoglobin’s affinity for oxygen change in the presence of carbon dioxide?
Its affinity is reduced
What is the Bohr effect?
The greater the concentration of Carbon Dioxide, the more rapidly haemoglobin releases its oxygen
Why is a transport system required?
To take materials from cells to exchange surfaces and the environment
What factors does the presence of a transport system depend on?
The surface area to volume ratio
How active an organism is
What are the features of transport system?
A suitable medium in which to carry materials
A form of mass transport
A closed system of tubular vessels
A mechanism for moving the transport medium within vessels
What do animals use as transport mechanisms?
Muscular contraction either of the body muscles or of the organs eg heart
What do plants rely on for exchange?
Natural, passive processes such as evaporation
What kind of circulatory system to mammals have?
A closed, double system
Why does the blood pass through the heart twice for reach circuit of the body?
Because pressure is reduced when the blood is passed through the lungs, and it otherwise would circulate the body very slowly
What is the atrium?
A thin walled and elastic chamber which stretches as it collects blood
What is the ventricle?
A much thicker, more muscular chamber
Why do the ventricles have thicker more muscular walls?
Because they have to contract strongly to pump blood a further distance
Where does the right ventricle pump blood to?
The lungs
Where does the left ventricle pump blood to?
The rest of the body
What are the two valves?
The left atrioventricular (bicuspid)
The right atrioventricular (tricuspid)
What is the problem with the large surface area needed for the capillaries in the lungs?
There has to be a significant drop in pressure
What is the aorta connected to?
The left ventricle
What does the aorta do?
Carries oxygenated blood to all parts of the body except the lungs
What is the vena cava connected to?
The right atrium?
What does the vena cava do?
Brings deoxygenated blood back from the tissues of the body
What is the pulmonary artery connected to?
The right ventricle
What does the pulmonary artery do?
Carried deoxygenated blood to the lungs where it is replenished with oxygen and carbon dioxide removed
What is the pulmonary vein connected to?
The left atrium
What does the pulmonary vein do?
Brings oxygenated blood back from the lungs
Which blood vessels supply the heart?
The coronary arteries
What is a myocardial infarction?
A heart attack
Where do the coronary arteries branch off from?
The aorta
What is systole?
Contraction
What is diastole?
Relaxation
What happens in diastole?
Blood returns to atria, pressure rises. AV valves open, blood passes into ventricles, pressure drops and semi lunar valves close
What happens in atrial systole?
Contraction of atrial walls forces blood into ventricles from atria
What happens in ventricular systole?
Ventricles fill with blood, wall contract, increasing pressure. AV valves shut and backflow prevented. Blood forced out into arteries
Where are the atrioventricular valves located?
Between the left atrium and ventricle and the right atrium and ventricle
What do the atrioventricular valves do?
Prevent backflow of blood when contraction of ventricles means that ventricular pressure exceeds atrial pressure
Where are the semi-lunar valves?
In the aorta and pulmonary artery
What do the semi-lunar valves do?
Prevent backflow of blood into ventricles when pressure in the vessels exceeds the pressure in the ventricles
Where are the pocket valves?
In veins
What is cardiac output?
The volume of blood pumped by one ventricle of the heart in one minute?
How would you calculate cardiac output?
heart rate x stroke volume
What do arteries do?
Carry blood away from the heart to the arterioles
What do arterioles do?
Smaller arteries that control the blood flow from arteries to capillaries
What do capillaries do?
Tiny vessels that link arterioles to veins
What do veins do?
Carry blood from capillaries back to the heart
What is the basic structure of arteries, arterioles and veins?
Tough fibrous outer layer Muscle layer Elastic layer Thin inner lining Lumen
What is the function of the tough fibrous layer?
Resists pressure changes from both within and outside
What is the function of the muscle layer?
Can contract and so control the flow of blood
What is the function of the elastic layer?
Helps maintain blood pressure by stretching and springing back
What is the function of the thin inner lining?
Smooth to reduce friction and thin to allow diffusion
What is the function of the lumen?
The central cavity, allows blood to flow
How are arteries adapted to their function?
Thick muscle layer to constrict and dilate
Thick elastic layer to come with high blood pressure
Thick wall to resist pressure
No valves
How are arterioles adapted for their function?
Muscle layer is thicker to allow constriction
Thin elastic layer because blood pressure is lower
How are veins adapted for their function?
Muscle layer is relatively thin as constriction and dilation can’t control blood flow
Elastic layer is thin due to low pressure
Overall thickness is small, low pressure
Valves throughout
How are capillaries adapted for their function?
Walls consist mostly of the lining layer
Numerous and highly branched
Narrow diameter to permeate tissues
Narrow lumen to squeeze RBCs flat
What is tissue fluid?
A watery liquid that contains glucose, amino acids, fatty acids, ions in solution and oxygen
How is tissue fluid formed?
High hydrostatic pressure at the artery end forces the fluid out through the capillary
What is ultrafiltration?
Filtration under pressure
How is tissue fluid returned to the circulatory system?
The loss of tissue fluid reduces hydrostatic pressure in capillaries, so higher hydrostatic pressure outside forces fluid back in. Water also leaves the tissue by osmosis.
How are fluids moved around the body?
Hydrostatic pressure o the tissue fluid
Contraction of body muscles
How does water move across the cells of the leaf?
Water from mesophyll cells is lost by evaporation from their cell walls to the air spaces in the leaf, then water moves by osmosis into the drier cells
What is the main factor responsible for the movement of water up the xylem?
Cohesion tension
How does water move up the xylem?
Water evaporates from mesophyll
Water molecules form hydrogen bonds and have cohesion
Water forms a continuous column down the xylem
The column is pulled up the xylem
What is transpiration pull?
When a column of water is pulled up the xylem as a result of transpiration
What evidence supports cohesion-tension theory?
Tree trunks change in diameter according to the rate of transpiration
If a xylem vessel is broken and air enters, a tree can no longer take up water
When a xylem vessel is broken, water does not leak out as it would if it was under pressure
What is needed to drive the process of transpiration?
Energy from the sun
What is translocation?
The process by which organic molecules and some mineral ions are transported from one part of a plant to another
What is the phloem?
The tissue that transports biological molecules in flowering plants
What are sources?
The sites of production of sugars
What are sinks?
The site of use or storage of sugars
What are the three stages of mass flow theory?
Transfer of sucrose into sieve elements from photosynthesising tissue
Mass flow of sucrose through sieve tube elements
Transfer of sucrose from the sieve tube elements into storage or other sink cells
What happens in transfer of sucrose into sieve elements?
Sucrose diffuses down a concentration gradient into companion cells from photosynthesising ones
Hydrogen ions actively transported using ATP into the companion cells
H+ diffuse down conc gradient into sieve tube elements
Co transport of sucrose with H+
What happens in the mass flow of sucrose through sieve tube elements?
Sucrose produced by source is actively transported into sieve tubes
Causes sieve tubes to have lower water potential
Water moves from xylem into sieve tubes by osmosis, creating high hydrostatic pressure
Sucrose and water actively enter sink due to low water potential and sucrose concentration
High hydrostatic pressure at source and low at sink causes mass flow of sucrose solution down gradient
What evidence supports mass flow theory?
There is a pressure within sieve tubes, shown by release of sap
Concentration of sucrose is higher in leaves (source) than roots (sink)
Downwards flow in phloem occurs in daylight but not at night
What evidence goes against the theory?
Function of sieve plates in unclear as they would seem to hinder mass flow
Not all solutes move at the same speed, they should do if the movement is by mass flow
What happens in transfer of sucrose from sieve tube elements into sink?
Sucrose is actively transported by companion cells out of sieve tubes and into sink cells
How can ringing be used to investigate mass transport in plants?
When woody stems are ringed, the upper region is seen to swell and the sap is seen to be rich in sugars and dissolved substances
What do ringing experiments show?
That the phloem is responsible for transport of sugars rather than they xylem
How can radioactive isotopes be used to investigate mass transport in plants?
Radioactively labelled CO2 can be used as it will be taken up by the plant and then incorporated into sugars. They can then be traced
What is evidence for the fact that translocation occurs in the phloem?
When phloem is cut, a solution of organic molecules flows out
Plants provided with radioactive carbon dioxide can be shown to have radioactively labelled phloem
