3.3.4.1-3.3.4.2 mass transport in animals & plants Flashcards
What do RBCs contain?
contains haemoglobin
Describe the structure of haemoglobin
- large water-soluble, globular protein w quarternary structure (made up of more than 1 polypeptide chain)
- 2 pairs of polypeptides chains (alpha and beta)
- each chain has a haem group, which contains an iron ion and gives Haemoglobin its red colour
how many molecules of oxygen can Haemoglobin carry?
- each molecule can carry four oxygen molecules
how and where is oxyhaemoglobin formed?
- in the lungs
- oxygen joins to haemoglobin in red blood cells to form oxyhaemoglobin
Hb + 4O2 –> HbO8
explain what happens in dissociation of oxyhaemoglobin
- reversible reaction
- when red blood cells reach tissue in body (e.g. muscle cells), oxygen is released from Oxyhaemoglobin and it turns back to haemoglobin
haemoglobin is found in all types of what animal?
vertebrates (e.g. earthworms, some insects, some plants and even in some bacteria)
If haemoglobin has a high/low affinity of oxygen, what does this mean?
high:
- take up (associates) oxygen more easily
- but release (dissociates) it less easily
low:
- take up (associates) oxygen less easily
- release it (dissociates) more easily
what must haemoglobin be able to do to make it efficient for transporting oxygen?
- readily associate w/ oxygen at surface where gas exchange takes place
- readily dissociate from oxygen at tissues requiring it
what is haemoblogin able to do under different conditions?
- change its affininity for oxygen under different conditions
describe the affintiy of haemoglobin for oxygen near gas exchange surfaces in terms of: oxygen concentration, carbon dioxide concentration, affinity of haemoglobin for oxygen and the result
oxygen conc: high
CO2 conc: low
affintiy of haemolglobin for O2: high
result: oxygen is associated
describe the affintiy of haemoglobin for oxygen near respiring tissues in terms of: oxygen concentration, carbon dioxide concentration, affinity of haemoglobin for oxygen and the result
oxygen conc: low
CO2 conc: high
affintiy of haemolglobin for O2: low
result: oxygen is dissociated
explain how DNA leads to different haemoglobin molecules having different affinities for oxygen
- affinity of oxygen to haemoglobin depends on haemoglobin structure
- different base sequences in DNA - different AA sequences - different tertiary/ quaternary structure and shape
- so different affinities for oxygen
what is the oxygen dissocation curve?
graph of the relationship between the saturation of haemoglobin with oxygen (%) and the partial pressure of oxygen (kPa)
name three factors affecting oxygen-haemoglobin binding
1 partial pressure of oxygen
2 partial pressure of carbon dioxide
3 saturation of haemoglobin
draw out and explain in detail the oxygen dissociation curve
- initially graph is shallow bc shape of haemoglobin makes it hard for first oxygen molecule to bind to one of the sites on its 4 polypeptide subunits bc they’re closely united (so in low O2 conc, little O2 binds to haemoglobin)
- once first O2 binded it changes the quarternary structure of haemoglobin, causing it to change shape. Makes it easier for other subunits to bind to an O2 molecule (more binding sites revealed!)
- therefore takes a smaller increase in partial pressure of oxygen to bind the 2nd oxygen molceule than the first (this is positive cooperativity bc binding of first makes second easier and so on).
- finally gradient begins to flatten out b/c likelihood of fourth oxygen finding a binding site is low (due to low probability)
what does a further left and further right oxygen dissociation curve indicate?
further left = greater affinity of haemoglobin for oxygen (loads oxygen readily but unloads it less easily)
further right = lower affinity of haemoglobin for oxygen (loads oxygen less readily but unloads it more easily)
explain the affinity of fetal haemoglobin
- fetal haemoglobin has higher affinity for oxygen than adult haemoglobin (curve further left).
- bc it must obtain oxygen from mother’s bloodstream as it doesn’t ventiate (by time oxygen reaches placenta, oxygen saturation in blood has decreased so ppO2 is low)
- this means fetal haemoglobin can bind to oxygen at lower partial pressure so foetus can survive low partial pressure
how does partial pressure of carbon dioxide affect oxygen-haemoglobin?
- as partial pressure of carbon dioxide increases, the conditions become acidic causing haemoglobin to change shape (this is bc CO2 reacts w/ water to form carbonic acid which lowers blood pH), affinity of haemoglobin for oxygen decreases, so oxygen released from haemoglobin
- known as bohr effect
what affect does a greater carbon dioxide concentration have on haemoglobin?
greater carbon dioxide concentration, the more readily the haemoglobin releases its oxygen (the bohr effect)
explain why oxygen binds to haemoglobin at a gas-exchange surface (e.g. THE LUNGS) and affect on oxygen dissociation curve?
- high pO2
- low carbon dioxide concentration in lungs
- therefore affinity of haemoglobin of oxygen increased (positive cooperativity (after first oxygen molecule binds, binding of subsequent molecules is easier)
- reduced CO2 conc has shifted oxygen dissociation curve to the left
why is carbon dioxide concentration low at a gas exchange surface?
because CO2 diffuses across exchange surface and is excreted from organism
explain why oxygen is released from haemoglobin in respiring tisssues (e.g. MUSCLES) and affect on oxygen dissociation curve?
- low pO2
- high carbon dioxide concentration
- CO2 dissolves in blood to form carbonic acid which makes blood acidic
- therefore affinity of haemoglobin of oxygen is reduced, this means oxygen is readily unloaded from haemoglobin into muscle cells
- increased CO2 conc has shifted oxygen dissociation curve to the right
describe the process of how the loading, transport and unloading of oxygen maintains sufficient oxygen for respiring tissues
- at gas-exchange surface, CO2 constantly being removed
- pH slightly raised due to low conc of CO2
- higher pH changes shape of haemoglobin and it loads oxygen more readily
- shape also increases affinity of haemoglobin for oxygen, so its not released while being transported in blood to tissues
- in tissues, CO2 produced by respiring cells
- CO2 is acidic in solution, so pH of blood within tissue lowered, lower pH changes shape of haemoglobin into one w/ a lower affinity for oxygen
- hameoglobin releases its oxygen into respiring tissues
(the more active a tissue, the more oxygen is unloaded)
describe how a higher rate of respiration leads to more oxygen available for respiration
higher rate of respiration - the more carbon dioxide the tissue produce - the lower the pH - greater the haemoglobin shape change - the more readily oxygen is unloaded - the more oxygen is available for respiration
how are llamas adapted to their environment in terms of their haemoglobin?
- live at high altitudes with low atmospheric pressure and so low pO2
- llamas have type of haemoglobin with higher affinity of oxygen so despite low pO2, it is still loaded onto haemoglobin
how are certain animals adapted to their environment in terms of their haemoglobin?
- animals like lugworms, whales and human foetuses have myoglobin
- myoglobin has v high affinity for oxygen, even at low partial pressures
- so it acts like an oxygen store, holding on to oxygen and dissociating until nearly all oxygen has been used up in cells
why is a circulatory system needed in some organisms?
- in large organisms their SA:V ratio isn’t large enough to rely on diffusion to supply substances like oxygen and glucose to cells that need it
- so a circulatory system is used
describe how lugworms efficiently transport oxygen to its tissues
- lugworms live on seashore, they’re not very active, most of the time they’re covered by sea water, which it circulates through its burrow
- oxygen diffuses into lugworm’s blood from water and it uses haemoglobin to transport oxygen to its tissues
- when tide goes out, lugworm can’t circulate fresh supply of oxygenated water through its burrow so has to extract as much oxygen as possible from its burrow
- so haemoglobin has high affinity for oxygen, meaning that haemoglobin of lugworm is fully loaded with oxygen even when theres little available in its environment
what two things depends on the SA:V ratio of an organism and how active the organism is, in terms of mass transport systems?
- the need for a specialised transport medium
- whether the specialised transport medium is circulated by a pump
name four common features of a mammalian circulatory system
1 suitable medium for transport e.g. blood
2 form of mass transport where transport medium is moved in bulk over large distance
3 closed system of tubular vessels that contains transport medium and forms branching network to distribute it to all parts of organism
4 mechanism for moving transport medium within vessels - requires a pressure difference between one part of the system and another
draw a diagram of human heart, including names of chambers, vessels, and valves
(picture saved in laptop as human heart anatomy)
relate the structure if the chambers to their function
atria: thin-walled and elastic, so they can stretch when filled with blood
ventricles: thick muscular walls pump blood under high pressure. The left ventricle is thicker than the right so it can contract to create enough pressure to pump blood all the way around the body
why do mammals have a closed, double circulatory system?
closed: blood confined to blood vessels
double: blood passes through the heart twice
how transport systems differ in animals and plants?
- animals use muscular contraction either of body muscles or of specialised pumping organ like heart
- plants rely on natural, passive processes like evaporation of water
why does blood through the heart twice?
- when blood passed through lungs, pressure is reduced, if it were to pass immediately to rest of body its low pressure would make circulation slow
- so blood returned to heart to boost its pressure before being circulated to rest of tissue
(necessary for organisms with high body temperature hence high metabolisms)
the vessels that make up the circulatory system of a mammal are divided into what three types?
- arteries
- veins
- capillaries
why are two pumps (left and right) needed instead of one?
- to maintain blood pressure around whole body
- when blood passes through narrow capillaries of longs, pressure drops sharply and therefore would not be flowing strongly enough to continue around whole body
- therefore it’s returned to the heart to increase the pressure
what is meant by a mass transport system?
movement of fluid in one direction
why do arteries require a large proportion of muscle and elastic tissue in their walls?
- heart causes high pressure in the arteries
- elastic tissue helps to regulate pressure
- smooth muscle helps to re-distribute blood
what is the function of a valve in the circulatory system?
forces blood to flow in one direction (prevents backflow of blood)
there are two circuits that make up the circulatory system, where do these two circuits transport blood to?
- heart and lungs
what is the cardiac cycle?
term used to describe the process of contraction and relaxation of the cardiac tissue
Explain the importance of maintaining a constant blood pH (3)
- Proteins like haemoglobin are affected by changes in pH
- The tertiary structure would be different
- Less oxygen would bind with the haemoglobin
what is diastole?
- in the cardiac cycle, period of relaxation of the heart muscle, accompanied by the filling of the chambers with blood
what is systole?
- phase of the heartbeat when the heart muscle contracts and pumps blood from the chambers into the arteries
why may vein be described as an organ?
Made up of different tissues
The oxygen dissociation curve of the fetus is to the left of that for its mother. Explain the advantage of this for the fetus (2)
- Higher affinity for oxygen
- So oxygen moves from the mother to the fetus
Explain how oxygen in a red blood cell is made available for respiration in active tissues (3)
- low pH due to increased co2 due to increased respiration
- means haemoglobin has increased dissociation
- oxygen diffuses from r.b.c to tissues
The haemoglobin in one organism may have a different chemical structure from the haemoglobin in another organism. Describe how (1)
different primary structure
The oxygen dissociation curve for haemoglobin shifts to the right during vigorous exercise. Explain the advantage of this shift (3)
- lowers affinity for oxygen
- releases o2 more readily to cells
- for rapid respiration
What are four valves of the heart, and which two categories are they divided into?
Atrioventricular valves: The tricuspid valve (between RA/RV) and mitral (bicuspid) valve (between LA/LV). They are located between the atria and corresponding ventricle.
Semilunar valves: The pulmonary valve (right semilunar valve, located between RV and pulmonary artery) and aortic valve (left semilunar valve, located between LV and aorta). They are located between the ventricles and their corresponding artery, and regulate the flow of blood leaving the heart.
role of ventricles and atria
ventricles: pump blood away from heart and into arteries
atria: recieve blood from veins
name an easy way to recall what heart chambers are attached to what blood vessels
A and V always go together
Atria link to Veins
Arteries link to Ventricles
name the four blood vessels, their role and location in the circulatory system
aorta: connected to LV and carries oxygenated blood to all parts of body except lungs
vena cava: connected to RA and brings deoxygenated blood back from tissues of the body (except the lungs)
pulmonary artery: connected to RV and carries deoxygenated blood to lungs, where its oxygen is replenished and its carbon dioxide is removed. Unusually for an artery, it carries deoxygenated blood
pulmonary vein: connected to left atrium and brings oxygenated blood back from the lungs. Unusually for a vein, it carries oxygenated blood
list the correct sequence of four main blood vessels and four heart chambers that a RBC passes through on its journey from the lungs, through the heart and body, and back to the lungs again
pulmonary vein - left atrium - left ventricle - aorta - vena cava - right atrium - right ventricle - pulmonary artery
suggest why its important to prevent mixing of the blood in the two sides of the heart
- mixing of oxygenated and deoxygenated blood would result in only partially oxygenated blood reaching tissues and lungs
- so supply of oxygen to tissues would be inadequate and there’d be a reduced diffusion gradient in the lungs, limiting the rate of oxygen uptake
describe how the heart muscle is supplied with oxygen
heart is supplied by its own blood vessels - coronary arteries
- they branch off into aorta after they leave the heart
what causes a myocardial infarction?
- blockage of coronary arteries by a blood clot
- bc area of heart muscle is deprived of blood and therefore oxygen
- muscle cells in region are unable to respire (aerobically) and so die
name the three stages of the cardiac cycle
cardiac diastole - entire heart relaxed atrial systole (or ventricular diastole) ventricular systole (or atrial diastole)
describe what happens during cardiac diastole.
- heart relaxed
- blood enters atria from pulmonary vein and vena cava, pressure starts to rise in atria
- when pressure exceeds that in the ventricles, atrioventricular valves pushed open (passage of blood aided by gravity)
- muscular walls of ventricles and atria still relaxed
- relaxation of ventricle walls causes them to recoil and reduces pressure within ventricle - causes pressure to be lower in aorta and pulmonary artery so semi-lunar valves in aorta and pulmonary artery close (dub sound of heart beat)
describe what happens during atrial systole
- atria contracts when around 50% empty, along with recoil of relaxed ventricle walls, forces remaining blood into the ventricles (from atria)
- throughout stage, muscle of ventricle walls remain relaxed
describe what happens in ventricular systole
- after short delay to allow ventricles to fill w blood, their walls contract simultaneously
- increases blood pressure within them. forcing atrioventricular valves and preventing backflow of blood into atria (lub sound)
- pressure increases in ventricles and once it exceeds that in aorta and pulmonary artery, blood is forced from ventricles into these vessels
describe why the left ventricle has a thicker wall than the right ventricle
- thick muscular walls which mean they contract more forcefully and higher pressure is created
- this is because thick left ventricle wall has to pump blood to extremities of body whereas right ventricle wall pumps blood to lungs
how are valves designed to control blood flow?
- designed so they open whenever difference in blood pressure either side of them favours movement of blood in required direction
- when pressure differences reversed i.e. when blood would tend to flow in opposite direction of whats desirable, valves designed to close
describe the role of atrioventricular valves
- prevent backflow of blood when contraction of ventricles mean that ventricular pressure exceeds atrial pressure
- closure of valves ensures that when ventricles contract, blood in them moves to aorta and pulmonary artery rather than back to atria
describe the role of semi-lunar valves
- in aorta and pulmonary artery
- prevent backflow of blood into ventricles when pressure in these vessels exceeds that in ventricles
- this arises when elastic walls of vessels recoil increasing pressure within them and when ventricle walls relax reducing pressure within ventricles
describe the role of pocket valves
- in veins that occur throughout the venous system
- ensure that when veins are squeezed, e.g. when skeletal muscles contract, blood flows back towards heart rather than away from it
what is cardiac output?
- the volume of blood pumped by one ventricle of the heart in one minute
- measured in dm3 min-1
- depends on two factors:
heart rate
stroke vol
how do you calculate cardiac output?
heart rate x stroke vol
HR (rate at which heart beats)
SV (vol of blood pumped out at each beat)
describe and explain the shape of the ventricular pressure line on a cardiac cycle graph
- low at first, gradually increases as ventricles fill with blood as atria contract
- left atrioventricular valves close and pressure rises dramatically as thick muscular walls of ventricles contract
- as pressure rises above that of aorta, blood forced into aorta past semilunar valves, so pressure falls as ventricles empty and walls relax
describe and explain the shape of the atrial pressure line on a cardiac cycle graph
- always relatively low bc thin atrial walls can’t create much force
- its highest when they’re contracting, but drops when left atrioventricular valve closes and its walls relax
- atria will then fill up w blood, which leads to gradual build-up of pressure until a slight drop when left atrioventricular valve opens and some blood moves into ventricle
describe and explain the shape of the aortic pressure line on a cardiac cycle graph
- rises when ventricles contract as blood is forced into aorta
- gradually falls (never below 12kPa) bc of elasticity of its wall, which creates a recoil action - essentially if blood is to be constantly delivered to tissues
- recoil produces temporary rise in pressure at start of relaxation phase
describe and explain the shape of the ventricular volume line on a cardiac cycle graph
- rises as atria contract and ventricles fill w/ blood
- drops suddenly as blood is forced into aorta when semilunar valves open
- volume increases again as ventricles fill with blood
what are arteries and their function?
- blood vessels that resist pressure changes from both within and outside
- transport high pressure blood from heart to tissues
what are arterioles?
smaller arteries that control blood flow from arteries to capillaries
what are capillaries and their function?
tiny vessels that link arterioles to veins
- exchange metabolic materials like oxygen, carbon dioxide and glucose between blood and body cells
what are veins?
blood vessels that carry blood from capillaries back to heart
describe the basic layered structure of arteries, arterioles and veins from outwards inwards
tough fibrous layer (resist pressure changes) muscle layer (contract and so control flow of blood) elastic layer (helps maintain blood pressure by recoiling) thin inner lining (endothelium) smooth to reduce friction and thin to allow diffusion lumen (central cavity of blood vessel throughout which blood flows)
arteries, arterioles and veins vs capillaries in transport
arteries, arterioles and veins carry out transport not exchange
only capillaries carry out exchange
describe how the structure of an artery is related to its function
- muscle layer thick compared to veins (means smaller arteries can be constricted and dilated to control vol of blood passing through)
- elastic layer is relatively thick compared to veins (b/c it’s important that blood pressure in arteries is kept high if blood is to reach extremities. Recoils during systole and diastole. This stretching and recoil action helps to maintain high pressure and smooth pressure surges created by beating of heart
- overall thickness of wall is great (resists vessel bursting under pressure)
- no valves (blood under constant high pressure due to heart pumping blood into arteries - so tends not to flow backwards
describe how the structure of arterioles is related to its function
- muscle layer is relatively thicker than in arteries (contraction of muscle layer allows constriction of lumen of arteriole, this restricts blood flow so controls its movement into capillaries that supply tissues with blood)
- elastic layer is relatively thinner than in arteries (b/c blood pressure is lower)
describe how the structure of a vein is related to its function
- muscle layer is relatively thin (compared to arteries) bc veins carry blood away from tissues and so their constriction and dilation can’t control blood flow to tissues
- elastic layer relatively thin (compared to arteries bc low blood pressure within veins won’t cause them to burst and pressure too low to create recoil action)
- overall thickness of wall is small (bc there’s no need for thick wall bc pressure within veins is too low to create risk of bursting. Also can be flattened easily, aiding blood flow within them
- valves at intervals throughout (to ensure blood doesn’t flow backwards, which it could bc pressure is low; when body muscles contract, veins compressed, pressurising blood within them, valves ensure that pressure directs blood in one direction - towards heart)
describe how the structure of capillaries is related to its function
- walls consist mostly of lining layer (making them very thin so diffusion distance is short, allows for rapid diffusion of materials between blood and cells)
- numerous and highly branched (so providing large SA for exchange)
- narrow diameter (so permeate tissues, which means no cell is far from a capillary and there’s a short diffusion pathway)
- lumen is so narrow (that RBCs squeezed flat against side of capillary, brings them even closer to cells to which they supply O2 - again reduces DD)
- there are spaces between endothelial cells (that allow WBCs to escape in order to deal w/ infections within tissues)
why aren’t capillaries the final journey of metabolic materials?
- capillaries are small, they can’t serve every single cell directly
- so final journey of metabolic materials is made into liquid solution that bathes tissues (tissue fluid)
what is tissue fluid?
- watery substance containing glucose, amino acids, oxygen and other nutrients
- supplies these to cells/tissue, while also removing any waste materials
- tissue fluid formed from blood plasma
how is tissue fluid formed?
- high hydrostatic pressure at arteriole end of capillary
- this forces fluid/water out of capillary
- proteins/large molecules stay in the capillary
- water potential of blood falls (becomes more negative)
- hydrostatic pressure falls
- due to friction/resistance to flow/narrow capillaries
- water moves back into the blood by osmosis at venuole end
- lymph system collects excess tissue fluid
How is the movement of Tissue fluid out of capillaries opposed?
- HP of tissue fluid outside capillaries resists outwards movement
- Lower water potential of blood due to plasma proteins causing water to move back into blood within the capillaries
what is the purpose of tissue fluid?
- once gases are in body they need to stay dissolved in some solution
- need to be dissolved or they’d form bubbles that’d impede blood flow and cause blockages
how do capillaries prevent cells and proteins from leaking out of them?
- capillaries have a little fibrous tissue around them
explain ultrafiltration in relation to the tissue fluid
- Pumping of heart creates high hydrostatic pressure at arterial end of capillary causing tissue fluid to move out of blood plasma
- Cells (e.g. RBCs) + proteins are too big to cross the membrane so are not transported
How does tissue fluid return back to the capillaries?
At venous end of capillaries water potential very low & hydrostatic pressure outside high,
therefore fluid with CO2 & waste products & water diffuses in
What happens to TF which does not return to the capillaries?
- Transported through lymphatic system
- contents moved by HP of tissue fluid and contraction of muscles that squeeze lymph vessels and valves in lymph vessel ensure right direction of blood flow (away from tissue to heart)
what is tissue fluid made from?
small molecules that leave the blood plasma
how do cells interact with tissue fluid?
they take in oxygen and nutrients from it, and release metabolic waste into it
how do substances move out of the capillaries?
pressure filtration/ultrafiltration
describe the process of how tissue fluid is returned to the circulatory system
- the loss of TF from capillaries reduce HP inside them
- so, by time blood reaches venous end of capillary network its HP usually lower than that of tissue fluid outside it
- so TF forced back into capillaries by higher HP outside them
- also, blood plasma has lost water and still contains proteins, so it has a lower WP than TF
- so, water leaves tissue by osmosis down a WP gradient
- Tf loses most of oxygen and nutrients by diffusion into cells its bathed, but gained CO2 and waste material in return
what happens to excess fluid in ultrafiltration of TF?
drained by lymphatic system
what is the lymphatic system?
system of vessels acting like a drain
what role does the lymphatic system play in ultrafiltration?
puts excess fluid back into the circulatory system
state what forces tissue fluid out of blood plasma in capillaries and into the surrounding tissues
hydrostatic pressure (HP) (due to pumping of the heart)
list the two routes by which tissue fluid returns to the bloodstream
via capillaries
via lymphatic system
how is water transported in plants?
through xylem vessels; long continous columns that also provide structural support to the stem
- process called transpiration
describe how a water potential gradient is estabished across the cells of a leaf
- mesophyll cells lose water to air apces by evaporation due to heat supplied by sun
- these cells now have a lower WP and so water enters by osmosis from neighbouring cells
- the loss of water these neighbouring cells lower their WP
- they, in turn, take in water from their neighbours by osmosis
- so WP gradient established that pulls water from xyelm, across leaf mesophyll and finally out into atmosphere
how can plants control their rate of transpiration?
- by changing the size of the stomatal pores
why do plants need a transport system?
- High metabolic demands
- Some plants are large
- Large SA:Vol for gas exchange (when stem, trunks and roots are included they have a small SA:Vol)
what are the 2 tissues in plants?
xylem and phloem
- found in vascular bundles
what does xylem tissue transport?
water and mineral ions in solution UP plant from roots
what does the phloem tissue transport?
organic substances (like sugars (in solution) UP AND DOWN plant
where are the xylem and phloem found?
Found together in vascular bundles in the leaves, stem and roots.
Describe the cohesion-tension theory of water transport in the xylem.
- water evaporates from mesophyll cells bc of heat from sun, leading to transpiration
- water molecules form H bonds between each other and cohere i.e. stick together
- water forms continuous, unbroken column across mesophyll cells and down xylem
- as water evaporates from mesophyll in leaf into the air spaces beneath stomata, more water molecules drawn up behind it bc of this ‘cohesion’
- column of water therefore pulled up xylem bc of transpiration - called transpiration pull
- transpiration pull puts xylem under tension i.e. negative pressure within xylem
state three cases of evidence to support the cohesion tension theory
- when xylem vessel broken, water doesn’t leak out, as it should if it were under pressure. Instead air is drawn in, which is consistent with it being under tension
- if xylem vessel broken and air enters it, tree can no longer draw up water. This is bc continous column of water is broken and so water molceules can’t stick together anymore (interrupted by air particles so h bonds are unable to form between water molecules)
- change in diameter of tree trunks; during day when transpiration at its greatest, theres more tension (negative pressure), this pulls xylem vessel walls inwards and causes trunk to shrink in diameter. At night when transpiration is at its lowest, there’s less tension in xylem so diameter of trunk increases
describe how the cohesion-tension theory helps explain water movements in plants
- transpiration from leaves at ‘top’ of xylem creates tension, which pulls more water into the leaf
- water molecules are cohesive, so when some are pulled into leaf others follow
- means whole column of water in xylem, from leaves down to roots, moves upwards, pulling water into stem through roots
what kind of process is transpiration
passive
- therefore doesn;t require metabolic energy to take place
what is needed to drive the process of transpiration?
- energy
- energy is in the form of heat that evaporates water from leaves and from leaves and it ultimately comes from the sun
what is transpiration?
the passive process where water evaporates out of the leaf, through the stomata, causing more water to be drawn from the soil
Explain how each of the following is related to the function of xylem tissue.
(i) Xylem tissue contains hollow tubes.
(ii) Lignin is present in xylem cell walls.
(i) unrestricted / free / quick / easy water flow / continuous column / maintains transpiration stream;
(ii) resists tension in water (column) / provides support / strength /
maintains column of water / adhesion / prevents water loss
what four main factors affect transpiration rate?
- light
- temperature
- humidity
- wind
how does light affect rate of transpiration?
- there’s positive correlation i.e. the lighter it is, the faster the rate of transpiration
- bc stomata open when its light to let in CO2 for photsynthesis
- when its dark stomata are usually closed, so there’s little transpiration
how does temp affect rate of transpiration?
higher temp, faster transpiration rate
- warmer water molecules have more energy to evaporate from cells inside leaf faster
- this increases conc gradient between inside and outside of leaf, making water diffuse out of leaf faster
how does humidity affect rate of transpiration?
- increased humidity leads to decreased transpiration;
- high humidity means more water in the air / increased saturation /
- reduced water potential gradient;
- slower rate of water loss / less evaporation;
how does wind affect rate of transpiration?
- windier it is, faster transpiration rate
- lots of air movement blows away water molecules from around stomata
- this increases conc gradient, which increases transpiration rate
describe the structure of xylem vessels
- very long, tube-like structures formed from dead cells (so can’t actively move water), joined end to end
- there are no end walls on these cells forming continuous, unbroken tubes from roots and leaves (essential for cohesion-tension theory of water flow up to the stem)
what’s translocation?
process by which organic molecules and some mineral ions are transported from one part of a plant to another
- carried out by phloem tissue
Explain how xylem tissue is adapted for its function.
long cells / tubes with no end walls;
continuous water columns;
no cytoplasm / no organelles / named organelle;
to impede / obstruct flow / allows easier water flow;
thickening / lignin;
support / withstand tension / waterproof / keeps water in cells;
pits in walls;
allow lateral movement / get round blocked vessels;
Explain the relationship between stomatal opening and photosynthesis.
- Stomata allow uptake of carbon dioxide;
2. Carbon dioxide used in / required for photosynthesis;
Describe and explain how water in the mesophyll cells passes out of the leaf.
(pathway from cells) along cell walls /
through spaces and out through stoma(ta);
by diffusion;
down a WP / diffusion / concentration gradient;
What are the three components of
phloem vessels?
Sieve tube elements= form a tube to transport sucrose in the dissolved form of sap.
Companion cells= involved in ATP production for active loading of sucrose into sieve tubes.
Plasmodesmata= gaps between cell walls where the cytoplasm links, allowing substances to flow.
describe the structure of the phloem
- made up of sieve tube elements, long thin structures arranged end to end
- end walls of sieve tube elements perforated to form sieve plates
- associated with sieve tube elements are cells called companion cells
what are sources and sinks in plants?
- ‘Source’ is the part of a plant where substances are produced (e.g. leaves for sucrose, amino acids) or enter the plant
- ‘Sink’ refers to the part of the plant where the substrate can be stored (e.g. roots or stem for starch)
name the hypothesis used to explain translocation in plants
the “mass flow” theory
Describe the mass flow hypothesis for the mechanism of translocation in plants.
[4/5 marks]
1 - solutes, e.g. sucrose produced by the source diffuses into the companion cells by facilitated diffusion. In here, sucrose actively transported into the sieve tube elements using ATP.
2 - this decreases the WP of the sieve tubes, causing water from the companion cells and the xylem to diffuse into the phloem by osmosis, increasing the HP.
3 - near the sink, sucrose is either used up in respiration or converted to starch for storage - either decreases WP of sink.
4 - so, water diffuses from the sieve tubes into the sink by osmosis, decreasing the HP in phloem.
5 - so, there’s a high HP gradient as there’s a high HP near the companion cells and a low HP near the sink. Therefore, there’s a mass flow of solutes throughout the plant.
how does sucrose in the leaf move into
the phloem?
- sucrose manufactured from products of photosynthesis
- sucrose diffuses down conc grad by FD from photosynthesising cells into companion cells
- H+ ions actively transported from companion cells into spaces within cell wall using ATP
- these H+ ions diffuse down conc gradient through carrier proteins into STE
- sucrose molecules transported along w/ H+ ions by co-transport (through co-transport proteins)
Give evidence for the mass flow
hypothesis of translocation
- sap is released when a stem is cut, therefore there must be pressure in the phloem/sieve tubes
- conc of sucrose higher in leaves (source) than in roots (sink)
- downward flow in phloem occurs in daylight, but ceases when leaves are shaded (or nighttime)
- increases in sucrose levels in leaf are followed by similar increases in sucrose levels in phloem a little later
- metabolic poisons/lack of oxygen inhibit translocation of sucrose in phloem
- companion cells posses many mitochondria and readily produce ATP
Give evidence against the mass flow
hypothesis of translocation
- function of sieve plates is unclear, as they’d seem to hinder mass flow
- not all solutes move at same speed, they should if movement is by mass flow
- sucrose delivered at more or less the same rate to all regions, instead of going quickly to ones with lowest sucrose conc, which is what MF theory would suggest
how does sucrose enter sink cells?
- sucrose actively transported by companion cells, out of sieve tubes and into sink cells
How can ringing experiments be used to investigate transport in plants?
- bark and phloem of a tree are removed in a ring, leaving behind the xylem.
- eventually the tissues above the missing ring swells due to accumulation of sucrose as the tissue below begins to die
- so, sucrose must be transported in the phloem.
How can ringing experiments be used to investigate transport in plants?
- bark and phloem of a tree are removed in a ring, leaving behind the xylem.
- eventually the tissues above the missing ring swells due to accumulation of sucrose as the tissue below begins to die
- so, sucrose must be transported in the phloem
How can tracing experiments be used to investigate transport in plants?
- Plants are grown in the presence of radioactive CO2, which will be incorporated into the plant’s
sugars - Using autoradiography, we can see
that the areas exposed to radiation correspond to where the phloem is, and other areas don’t blacken with film so they don’t carry sugars - shows phloem alone is responsible for their translocation
suggest difference there would be between results of ringing experiment carried out in the summer and one carried out in the winter. Explain reason for difference suggested
- large swelling above ring in summer but little, if any, swelling in winter
- in summer rate of photosynthesis, so sugar production is greater bc of higher temps, longer daylight and higher light intensity; translocation of these sugars lead to their accumulation
- in winter there is lower temps, shorter daylight and lower light intensity; photosynthesis rate is less, less sucrose available. So less sucrose to accumulate than in summer
why is smoking a risk factor for cardiovascular disease?
- CO combines w/ haemoglobin instead of oxygen, so reduces amount of oxygen delivered to tissues, to catch up blood has to work harder, results in increased blood pressure (leads to possible myocardial infraction)
- nicotine causes adrenaline release, increasing heart rate and blood pressure.
- nicotine makes blood more sticky, making a thombrosis more likely
why is high blood pressure a risk factor for cardiovascular disease?
- prolonged stress, certain diets, lack of exercise can cause high BP
- high BP means heart must work harder
- vessels more likely to burst under high pressure, could cause a haemorrhage
- to resist pressure, arterial walls harden which reduces blood flow and so amount of O2 and glucose going into tissues is less
two advantages of right ventricle having a less thicker wall than the left ventricle
less thick means blood travels in vessels under lower pressure
- lower blood pressure means slower-moving blood through the capillaries which allows enough time for exchange at the alveoli
- a high blood pressure would damage the (thin) capillaries
what is myoglobin?
- red pigment in muscles
- stores oxygen (emergency store, when rate muscles use oxygen exceeds rate muscles are supplied with oxygen)
- single polypeptide (1 haem group = takes up 1 molecule of O2)
- only used when haemoglobin supply is used up
describe the positions of myoglobin, foetal haemoglobin and adult haemoglobin on an oxygen dissociation curve, relative to one another
- myoglobin shifted furthest left, then foetal haemoglobin and then adult haemoglobin
- therefore myoglobin has greatest affinity for oxygen in lower partial pressures
describe the biological significance of myoglobin shifted further left on the oxygen dissociation curve
- myoglobin has a greater affinity for oxygen (myoglobin is an oxygen store)
- oxygen will be transferred to myoglobin/muscle from adult haemoglobin
describe the advantage of foetal haemoglobin being shifted left on the oxygen dissociation curve
- more saturated than maternal haemoglobin/greater affinity for oxygen
- at all oxygen partial pressures
- oxygen will pass from maternal to foetal blood
suggest how myoglobin can peform a useful function in muscle tissue
- myoglobin has a high affinity for oxygen at very low partial pressures
- acts as an oxygen store
- used when muscle is exercising heavily/working hard (muscle contractions)
state 1 difference between fetal haemoglobin and adult haemoglobin and give one reason why this difference is essential to fetus
difference:
fetal haemoglobin has a higher affinity for oxygen at the same partial pressures
reason:
fetal haemoglobin needs to be able to bind to oxygen under low partial pressures in placenta/when adult oxyhaemoglobin dissociates
what’s cardiac output?
volume of blood being pumped by the heart into the circulatory system in one minute
CO = stroke volume x heart rate
- units: ml/min or l/min
what are cardiomyocytes?
heart muscle cells that make a lot of tissue in heart
define stroke volume and heart rate
SV (ml/l) -is the volume of blood pumped out of each ventricle each time the heart beats
HR (bpm) - number of beats per minute and is the same as your pulse rate
what is the function of the coronary arteries?
to carry (oxygenated) blood/glucose to heart muscle/tissue/myocytes
explain the importance of maintaining a constant blood pH
- haemoglobin (or another named protein/enzyme) affected by change in pH
- change to tertiary structure
- (how it affects named protein/enzyme function) haemoglobin can’t bind to as many O2
the hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why.
- loss of water/fluid
High blood pressure leads to the accumulation of tissue fluid. Explain how
- high blood pressure = high hydrostatic pressure
- increases outward pressure from arteriole end of capillary
- so more tissue fluid formed
an arteriole is described as an organ, describe why
made up of more than one tissue
an arteriole contains muscle fibres. Explain how these muscle fibres reduce blood flow to capillaries
muscle fibres in arteriole contract narrows arteriole (reduces lumen size/diameter)
Blood flow in capillaries is slow. Given an advantage of this
more time for exchange/diffusion (of substances)
explain why a lack of protein in the blood causes a build-up of tissue fluid
- Water potential (in capillary) not as low/is
higher/less negative / water potential gradient is
reduced; - Less/no water removed (into capillary);
- By osmosis (into capillary);
explain why pressure for xylem is negative
(Inside xylem) lower than atmospheric pressure
/ (water is under) tension;
The thickness of the aorta wall changes during each cardiac cycle. Explain why [3 Marks]
- (Aorta wall) stretches;
- Because ventricle/heart contracts / systole /
pressure increases; - (Aorta wall) recoils;
- Because ventricle relaxes / heart relaxes
/diastole / pressure falls; - Maintain smooth flow / pressure;
Describe how tissue fluid is formed and how it is returned to the circulatory system [6 Marks]
Formation
1. High blood / hydrostatic pressure / pressure
filtration;
2. Forces water / fluid out;
3. Large proteins remain in capillary;
Return
4. Low water potential in capillary / blood;
5. Due to (plasma) proteins;
6. Water enters capillary / blood;
7. (By) osmosis;
8.(equilibrium reached, some absorbed into lymphatic system, travels in lymph vessels and drained into blood vessels near heart)
Explain how water enters the xylem from the endodermis in root and is then transported to the leaves [6 MARKS]
(In the root)
1. Casparian strip blocks apoplast pathway /
only allows symplast pathway;
2. Active transport by endodermis;
3. (Of) ions/salts into xylem;
4. Lower water potential in xylem / water enters
xylem by osmosis /down a water potential
gradient;
(Xylem to leaf)
5. Evaporation / transpiration (from leaves);
6. (Creates) cohesion / tension / H-bonding
between water molecules / negative pressure;
7. Adhesion / water molecules bind to xylem;
8. (Creates continuous) water column
Explain the role of the heart in the formation of tissue fluid [2 marks]
- Contraction of ventricle(s) produces high
blood / hydrostatic pressure; - (This) forces water (and some dissolved
substances) out (of blood capillaries);
Lymphoedema is a chronic condition that causes swelling in the body’s tissues. Suggest how a blockage in the lymphatic system could cause lymphoedema.
[1 mark]
Excess tissue fluid cannot be (re)absorbed /
builds up;
Describe the pathway taken up by an oxygen molecule from an alveolus to the blood [2 MARLS]
- (Across) alveolar epithelium;
2. Endothelium/epithelium of capillary;
describe the advantage of the bohr effect during intense exercise [2 Marks]
- increases dissociation/unloading of oxygen
- for aerobic respiration at tissues/muscles/cells
explain the importance of elastic fibres in the wall of the aorta [2 Marks]
- allows for recoil/stretch to smooth blood flow/maintain high blood pressure
Explain the importance of muscle fibres in the wall of an arteriole
- muscle contracts
- reduces/regulates blood flow (to capillaries)
Efficient exchange of substances in the capillaries is linked to the rate of blood flow. Explain how
- more time for exchange of substances (nutrients and respiratory gases)
The student cut the shoot and put in the potometer under water. Explain why
prevent air entering/continuous water column
To calculate the rate of water uptake by the shoot in cm3 per minute in a potometer, what measurements do you need to make?
- distance and time
- diameter of capillary tube
The student assumed water uptake was equivalent to the rate of transcription, Give two reasons why this might not be a valid assumption
- apparatus not sealed/leaks
- water might be used in photosynthesis (i.e. not all water transpired)
- also used to provide support/turgidity
Suggest how the reservoir in the photometer allows repeat measurements to be made. Also suggest why she made repeat measurements
- returns bubble to start
- have higher/greater reliability and find anomalies in results
