Mass Trasnsport Flashcards
Why do large organisms have a transport system
Organisms exchanges materials between themselves and their environment
Multicellular organisms like mammals and plants have a small surface area to volume ratio so they need a specialised transport system to carry organisms between specialised exchange surfaces and cells
Whether or not there is a specialised transport medium and whether or not it is circulated by a pump depends on two things
The surface area to volume ratio
How active the organism is
The smaller the surface are to volume ratio and the more active the organism is
The greater the need for a specialised transport system with a pump
Haemoglobin
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Part of human circulatory system
Found in erythrocytes (RBC)
Has evolved to make it efficient at loading oxygen in some sets of conditions and unloading in a different set of conditions
Different chemical types of haemaglobin all with the same function
Haemaglobin also found in earthworms, insects, plants, bacteria
Protein molecule with quaternary structure, contains 4 polypeptide chains, 2 alpha and 2 beta
Each subunit has 1 polypeptide and a haem group which contains a single iron ion
The Fe2+ has a high affinity for oxygen
Each haemaglobin can bind to 4 oxygens as there are 4 subunits
In lungs, oxygen binds to haemaglobin to form oxyhaemaglobin
Reversible reaction
Asssociation / loading
The process by which haemoglobin binds with oxygen
In humans take place in lungs
Dissociation / unloading
The process by which haemoglobin releases oxygen
In humans takes place in respiring tissue
Oxyhaemoglobin dissociation curve
Shows how saturated the haemoglobin is with oxygen at any given partial pressure of oxygen
Partial pressure of oxygen is a measure of oxygen concentration in the tissues
Graph is an S shape because
AT low oxygen partial pressure
3
The haemoglobin does not easily bind oxygen
Because the haem groups are in the centre of the haemoglobin making it difficult for oxygen to bind
Results in a low saturation level at low oxygen pp
Graph is an s shape because
As oxygen pp increases
4
Diffusion gradient into the haemoglobin increases
This means that eventually an oxygen molecule will associate with one of the haem groups
This results in a change in the shape of the haemoglobin molecule and makes it easier for more oxygen molecules to associate with the other haem groups.
Therefore the gradient of the curve increases as the oxygen partial pressure does.
Graph is an s shape because
High oxygen pp
2
It is difficult for all the haemoglobin molecules to become 100% saturated
This is because it is difficult for the last oxygen to diffuse and associate with the fourth haem group
Partial pressure of carbon dioxide
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Measure of carbon dioxide concentration in a cell
Can effect oxygen unloading
Haemoglobin unloads its oxygen more readily at a higher pCO2
When cells respire they produce CO2 which raise pCO2
This increases the rate at which oxyhaemoglobin dissociates to form haemoglobin and oxygen
The dissociation curve therefore shifts to the right . BOHR EFFECT
Bohr effect
2
Results in more oxygen being released when more carbon dioxide is being produced
This means that when exercising the muscles can be supplied with more oxygen for continued aerobic respiration
Different types of haemoglobin
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Different organisms have different types of haemoglobin with different oxygen-transporting capacities
It depends on where they live, how active they are and their size
Having a particular type of haemoglobin is an adaptation that helps organisms survive in a particular environment
Low oxygen environment
Different types of haemoglobin
Organisms in an environment with low conc of oxygen have haemoglobin with a higher affinity for oxygen than human haemoglobin
This is because there isn’t much oxygen available, so the haemoglobin has to be very good at loading any available oxygen.
Dissociation curve to the left of humans
High activity levels
Different types of haemoglobin
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Organisms that are active ave a high oxygen demand so have haemoglobin with a lower affinity for oxygen than human haemoglobin
This is because they need their haemoglobin to easily unload oxygen so that its available to use
The dissociation curve is to the right of a humans
Size
Different types of haemoglobin
Small mammals tend to have a higher surface area to volume ratio than larger mammals
This means they lose heat quickly, so have a high metabolic rate to help keep them warm, therefore have a high oxygen demand
They have haemoglobin with a lower affinity for oxygen than human haemoglobin.
This is because they need their haemoglobin to easily unload oxygen so that its available to use
Dissociation curve to the right of a humans.
Mammals have a CLOSED, DOUBLE circulatory system
Closed= blood is confined to vessels
Double= blood passes twice throug the heart for each complete circuit of the body.
Blood transports 4 around the body
Respiratory gases
Products of digestion
Metabolic waste products
Hormones
Structure of heart
LEARN
Right side of the heart
Pumps deoxygenated blood to the lungs
Left side o the heart
Pumps oxygenated blood to the whole body
Four chambers in the heart
2 atria 2 ventricles
Ventricles ave thicker muscle walls so they can push blood out of the heart wheras atria just need to push blood a short distance into ventricles
Left ventricle muscle is much thicker which allows it to contract more powerfully ad pump blood all the way around the body because the length of blood vessels through which blood has to flow is longer.
Right side is less muscular so it’s contractions are only powerful enough ro pump blood to nearby lungs.
The septum
Separates the two sides of the heart so oxygenated and deoxygenated blood do not mix
Also enables different pressures on each side
Although oxygenated blood passes through the left side of the heart,
The heart does not use this oxygen to meet its own respiratory needs
Instead the heart has its own blood supply, left and right coronary artery
No oxygen on the right side of heart
Walls are too thick so long diffusion distance.
Arteries carry blood
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From the heart to the rest of the body
Divide into smaller artérioles
Form a network throughout the body
Artery structure
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Lumen is small to maintain the blood pressure
Collagen fibres and fibrous proteins means the thick wall can with stand high pressure
The elastic tissue allows trhe wall to stretch and recoil , maintains diastolic pressure
Endothelium is smooth to reduce friction and is folded so can unfold when artery stretches
Smooth muscle allows contraction and vasoconstriction which narrows the lumen of the artery. In artérioles,the muscle enables blood to be directed to different areas of demand in the body. Muscle contracts to restrict blood flow and releases to allow full blood flow.
Veins carry blood
Back to the heart
Vein structure
Lumen is large to ease blood flow
The walls have less collagen, smooth muscle and elastic tissues as they do not need to perform the roles of the artery
Walls are thin but still strong
Contains valves as there is a very low pressure to prevent back flow
To move blood through the veins back to the heart pressure is exerted by the movement of the muscles
There is also some residual pressure from the contraction of the left ventricle muscle wall.
Blood is at a very high pressure in arteries because
The contraction of the left ventricle muscle
Pressure in capillaries
High at the artérioles end due to the contraction of the left ventricle wall but the pressure falls as it goes towards the venous end
Arterioles branch into
Capillaries
Smallest of blood vessels
Molecules are exchanged between capillaries and cells
Capillaries structure
The walls are made up of a single layer of flattened endothelial cells high reduces the diffusion distance
The narrow lumen which is the same diameter as a red blood cell ensures that the cells are squeezed as they travel through the capillaries,This reduces diffusion distance meaning more oxygen an diffuse
Smooth endothelium reduces friction for blood flow
Gaps between endothelial cells slows movements of nutrients proteins cannot pass
Large SA , cross sectional area allowimng more exchange
Many pores, water and solutes can pass through
Blood flows through slowly giving it time for molecules to dissolve.
Formation of tissue fluid
1+5
Occurs at the arterial end
- Blood under high hydrostatic pressure due to the contraction of the left ventricle muscle of the heart
- Water in the blood is forced out of tiny gaps in the capillary wall
- This fluid contains dissolved substances such as oxygen and glucose, cells and plasma proteins retained in the capillary as they are too big to fit the rough the gaps in the endothelium of the capillary
- The fluid is now known as tissue fluid and as it surrounds the cells and allows the movement of substances across the plasma membranes
- This type of filtration under pressure is called ultrafiltration
Return of fluid to the capillary
Occurs at venous end of the capillary
- Blood has lowER hydrostatic pressure
- Retention of the plasma proteins means the plasma has a lower water potential compared to the tissue fluid
- There is a small amount of hydrostatic pressure being exerted by the tissue fluid
- Theses two factors resul in the tissue fluid entering the capillary carrying carbon dioxide and other waste products from the cells.
Systole
Contraction of cardiac muscle
Diastole
Relaxation of cardiac muscle
Cardiac cycle lasts
Heart rate of
0.8 seconds
75 beats per min
Cardiac cycle stage 1
Atria fill with blood
Atria contract, atrial systole, decreasing the volume of the atria and increasing the pressure inside the chambers-
Blood is squeezed into ventricle via atrioventricular valve
VENTRICLES RELAX, ATRIA CONTRACT
Cardiac Cycle stage 2
Ventricles contract decreasing their volume and increasing the pressure inside the chambers
The pressure inside the ventricle becomes higher than the pressure inside the atria forcing the atrioventricular valves shut to prevent back flow
The pressure in the ventricles is also higher than that of the arteries which forces the semi lunar valves open
VENTRICLES CONTRACT, ATRIA RELAX
Cardiac cycle stage 3
Ventricles and atria both relax, diastole
The higher pressure in the arteries than ventricles causes the semi lunar valves to close to prevent back flow of blood into the ventricles
Atria fill with blood
The cycle starts again
VENTRICLES RELAX, ATRIA RELAX
Tendinous chords
Stop the flaps that make up the atrio ventricular valve everting , when the valves close.
Valves are open when
The pressure in the chamber before te valve is greater than in the chamber after it
Atrioventricular valves open when
The pressure in the atria is greater than the ventricles
Semi lunar valves open when
The pressure in the ventricles is greater than the arteries
Valves closed
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When the pressure in the chamber after the valve is greater than in the chamber before it
The valves will close to prevent the back flow of blood
The lib dub sound the heart makes is due to the closing of the atrioventricular valve followed by the closing of the semilunar valve
Électrocardiogramme
Monitors the electrical activity of the heart
Electrical activity generated by the hearts spreads through the tissue nearby
Sensors on the skin pick up the electrical excitation created by the heart and turn it into a trace
Cardiac output is
The volume of blood pumped by the heart per minute
Cm^3 per min
Cardiac output equation
Cardiac output =
stroke volume x heart rate
Heart rate= number of beats per min
Stroke volume= the volume of blood pumped during each heartbeat, measured in cm^3
Blood
Blood contains cells, red blood cells, white blood cells and platelets)
And. Watery fluid called plasma
Plasma contains dissolved substances:
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Oxygen Carbon dioxide Salts Glucose Fatty acids Amino acids Hormones Plasma proteins
Tissue fluid
Similar composition to plasma but doesn’t contain any plasma proteins
It’s role is to transport oxygen and nutrients from the blood to the cells and carbon dioxide and other waste products from the cells back to the blood
Formation of tissue fluid occurs at a capillary network which surrounds cellls
Once tissue fluid has exchanged molecules with the cells, it is returned to the circulatory system
Most tissue fluid returns to the bloood plasma directly via capillaries
Formation of tissue fluid
Occurs at the arteriole end
- Blood under hig hydrostatic pressure due to the contraction of the left ventricle muscle of the heart
- Water in the blood is forced out of tiny gaps in the capillary wall
- This fluid contains dissolved substances such as oxygen and glucose, cels and plasma proteins are retained in the capillary as they are too big to fit through the gaps in the endothelium of the capillary
- The fluid is now known as tissue fluid and as it surrounds the cells and allows the movement of substances across the plasma membrane
- Called ultrafiltration
Return of fluid to the capillary
Occurs at the venous end of the capillary
- Blood has lower hydrostatic pressure
- Retention of the plasma proteins means the plasma has a lower water potential compared to the tissue fluid
- There is a small amount of hydrostatic pressure being exerted by the tissue fluid
- These two factors result in the tissue fluid entering the capillary carrying carbon dioxide and other waste products from the cells
Lymph
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Not all the tissue fluid can return to the capillaries
Remainder is carried back by the lymphatic system
A system of vessels that begin in the tissues
Lymph vessels
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Form a secondary drainage system returning some tissue fluid to the blood stream via the subclavian vein in the neck
If lymph vessels become blocked, swelling can occur in the affected limbs due to accumulation of tissue fluid
Lymph fluid
Has a similar composition to tissue fluid but with more lipids and carbon dioxide but less oxygen and nutrients
Lymph nodes
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Situated in the armpit, groin, neck and gut
Produce lymphocytes which intercept bacteria and viruses and help prevent the spread of microbial on section in the body
Lymphatic system is involved with
3
Draining excess tissue fluid and returning it to the blood
Immune system- produces lymphocytes
Absorption of lipids from the digestive system
Cardiovascular disease is
A general term used to describe diseases asssociated with the heart and blood vessels
Cardiovascular diseases include
Aneurysms
Thrombosis
Myocardial infarction
Stroke
Most cardiovascular diseases start with
Atheroma formation
Coronary heart disease is
A type of cardiovascular disease
Occurs when coronary arteries have lots of atheromas which restricts blood flow to the heart muscle
Atheroma formation
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Following damage to the artery endothelium, there will be the accumulation of fatty deposits called atheroma under the endothelium at the site of the damage .
If the atheroma breaks through the inner lining of the artery, it forms a plaque which roughens the wall of artery and reduces the lumen size of the artery
This restricts blood flow which causes the blood pressure to increase and can cause clots.
Aneurysm
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A balloon like swelling of the artery.
It starts with the formation of atheromas
Atheroma plaque damages and weakens arteries
They also narrow arteries, increasing blood pressure
When blood travels through a weakened artery at high pressure, it may push the inner layers of the artery’s through the outer elastic layer to form an aneurysm
This may burst causing a haemorrhage (bleeding)
Thrombosis
4
Formation of a blood clot
An atheroma plaque can rupture the endothelium of the artery , damaging the artery wall
Platelets accumulate at the site of the damage and form a blood clot
This clot can cause complete blockage of the artery lumen, or block a vessel elsewhere in the body
Myocardial infarction (heart attack) 4
Atheroma becomes unstable, a piece may break off damaging the artery wall and leading to a blood clot forming
If the blood clot blocks the coronary artery, the heart muscle is starved of blood , receiving no oxygen and glucose - heart attack
Symptoms incluse pain in the chest and upper body, shortness of breath and sweating
If large areas of the heart muscle are affected, complete heart failure can occur- often fatal.
Stroke
3
Death of part of the brain tissue due to lack of oxygen and glucose being delivered to the tissue because of either;
- blockage caused by a blood clot travelling to the arteries in the brain resulting in loss of blood flow to part of the brain
- artery bursting (haemorrhage )
Stroke symptoms
FAST
Face- distorts on one side
Arms- weakness of limbs on one side of the body
Speech- difficulty speaking
Time- call the hospital as soon as possible, there will also be sudden confusion
Risk factors for cardiovascular disease
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Age Gender- men at higher risk Smoking- carbon monoxide+ nicotine Hypertension(high blood pressure)- increase risk of damage to artery linings Obesity Physical inactivity High conc of low density lipoproteins in blood Diet high in salt Diet high in saturated fats- increases conc of LDL Lack of vitamins Type 2 diabetes Stress Family history of cardiovascular disease
Two tissues important for mass transport in plants
Xylem
Phloem
Xylem tisssue
Transport water and mineral ions up the plant from root to leaves
Transpiration
Phloem tissue
Transports assimilates eg sucrose up ne down the plant
Translocation
Structure of xylem
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Dead cells aligned end to end
No end walls- forms continuous tubes from root to leaf
No nucleus and no cytoplasm- hollow tubes
Walls thickened(lignified) to prevent tubes collapsing and waterproof the walls of the cells
The lignin thickening in the cell walls forms patterns which can be spiral, rings(annular) or a network of broken rings (reticulate), this prevents the vessel from being too rigid and allows flexibility in the stem and branch
Bordered pits- in some places the lignification is incomplete leaving pores in the wall of the vessel, allowing water to pass into an adjacent vessel or a living part of the plant, this gives water a path around any blockages.
Water movement up a plant
Cohesion tension theory
- Water evaporates from the surface of mesophyll cells by transpiration
- Water moves out of the xylem by osmosis to replace that lost from mesophyll cells down WP gradient
- This creates. Tension in the xylem
- As water moves out of the xylem, low pressure forms at the top of the xylem. This creates a suction from the top of the plant which pulls water up.
- Water molecules are cohesive (stick together) due to hydrogen bonds between molecules so when some are pulled into the leaf, others follow. Whole column of water in the xylem is pulled upwards
- The cohesion stops the water column in the xylem breaking under tension
- Water then enters by osmosis the stem through the roots.
Transpiration is
The loss of water vapour from the aerial parts of the plant, such as through stomata in the leaf
Transpiration
Water movement through leaves involves three processes
- Osmosis from the xylem to the mesophyll cells
- Evaporation from the surface of the mesophyll cells into the intercellular space
- Diffusion of water vapour from the intercellular spaces out through the stomata
Transpiration stream means that
As water is lost from the xylem in the leaves it is replaced from below
Water ill move through the xylem from the roots to replace what has. Been lost .
Transpiration importance
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Water is required in the leaves for photosynthesis
Water is required to enable cells to grow ne elongate
Water keeps cells turgid
The flow of water carries useful mineral ions up. The plant
Evaporation of water keeps the plant cool
How number of leaves affects water loss
More leaves= increased SA- more water lost by transpiration
How larger surface area affects water loss
If leaves have many stomata, then more water is lost quickly
If stomata are on the lower surface, water vapour is lost slower
How waxy cuticle affects water loss
Thicker cuticle reduces evaporation, impermeable to water vapour
How light affects water loss
In light, stomata open to allow more gas exchange for photosynthesis therefore more water lost via evaporation
How temperature affects water loss
Increased temperature increases the kinetic energy of the water molecules
More water vapour is lost via stomata
Faster evaporation and diffusion
How relative humidity affects water loss
Increased humidity, decreases evaporation from the leaf as there is a smaller water potential gradient, between air spaces in the leaf and the air outside
How air or wind movement affects water loss
More wind removes more water vapour from the leaf surface. Therefore increases the water potential gradient and so increases the rate of transpiration so more water lost.
How water availability affects water loss
Decreased water available, steam
Xerophytes
Plants which can survive in dry places such as deserts and sand dunes
Have adaptations to reduce water loss
Xerophyte adaptations
Smaller leaves= reduces surface area so decreases water vapour loss by transpiration
Thick waxy cuticle= reduces evaporation, transpiration, from leaf surface
Stomata close when very hot= reduces water loss when water availability is low
Hairs on leaf surface, trichomes= traps a layer of water vapour in the pit close to the surface of the leaf decreasing the water potential gradient
Stomata sunk in pits= traps water vapour in the pit close to the surface of the leaf decreasing the water potential gradient
Rolling of leaves= traps water vapour in the rolled leaf decreasing the water potential gradient. Reduces surface area
Loss of leaves= cannot lose water through stomata in the leaf by. Transpiration
High salt conc in cells= decreases the water potential gradient in cells, less water lost between cells
(Some)Only open stomata at night= store CO2 for use in the day.
Phloem tissue consists of
Sieve tube elements and companion cells
Sieve tube elements
7
Have little cytoplasm, few organelle but no nucleus
Do not have lignified walls
Have cross walls at intervals called sieve plates
Sieve plates connect the elements
Sieve plates allow the sap to flow easily
Elements are lined up end to end to form a tube which allows the plant to transport assimilates, mainly sucrose
Plasmodesmata link the cytoplasm of companion cells and sieve tube elements
Companion cells
2
Have cytoplasm and many mitochondria which produce ATP for active transport
They will also have many proteins in the plasma membrane and may ribosomes
Translocation
The movement of assimilates
An energy requiring process (ATP) in the phloem
Moves assimilates from source to sink
Assimilates
Solutes
Such as amino acids and sugars like sucrose
Source
Part of the plant that releases assimilates
Sink
Part of the plant that receives assimilates
Active loading - loading the sucrose int the phloem
3
- The companion cells use ATP to actively transport/ pump hydrogen ions out of their cytoplasm and into the surrounding tissue
- This sets up a concentration gradient and the hydrogen ions diffuse back into companion cells with the sucrose. The diffusion occurs through cotransporter proteins . These proteins allow the hydrogen ions to bring the sucrose molecules into the companion cells
- As the concentration of sucrose molecules builds up i the companion cells they diffuse into the sieve tube elements through numerous plasmodesmata
Mass Flo hypothesis
At the source
3
Active transport is used to actively load (ATP and carriers) the sucrose into (companion cells) the sieve tube elements, reducing the water potential
Water enters the sieve tube bu osmosis from the surrounding tissue
This increases the hydrostatic pressure in the sieve tube elements.
Mass flow hypothesis
At the sink
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The solutes are being used at the sink
Sucrose may be converted into starch or be used for respiration
The sucrose leaves the sieve tube elements at the sink via diffusion or active transport
This increases the water potential in the sieve tube element
Water molecules move out of the sieve tube by osmosis down WPG
This reduces the hydrostatic pressure in the sieve tube elements
The pressure gradient means that the phloem sap moves from source to sink
Evidence for mass flow
4
- Use of aphids= an aphid feeding on a plant stem can be used to show that the mouthparts which are feeding from the phloem contain sugars. Pressure in the phloem can be investigated using aphids. The sap flows out quicker nearer the leaves than further down the stem- evidence there is a pressure gradient
- Ringing a tree= removing a ring of bark, include phloem but not xylem. A bulge forms above the ringed area because the sugars cant pass the ringed area. This decreases the water potential and water moves into the cells. Ringing is evidence that there can be a downward flow of sugars.
- Radioactive tracers= tracers such as radioactive carbon (14C) can be used to track the movement of organic substances in a plant.
- Metabolic inhibitors= translocation can be stopped by using a metabolic poison that inhibits the formation of ATP - evidence that active transport is involved
Evidence against mass flow
2
- Sugar travels to many different sinks, not just one with the lowest hydrostatic pressure, as the model suggests
- The sieve plates would create a barrier to mass flow. A lot of pressure would be needed for the solutes to get through at a reasonable rat.
