3.3.4 mass transport Flashcards
(260 cards)
1
Q
what are the haemoglobins?
A
The haemoglobins are a group of chemically similar molecules found in many different organisms
2
Q
does the type of haemoglobin an organism has vary
A
type of haemoglobin an organism has varies depending on where they live/way of life
3
Q
give an example of a mass transport system
A
circulatory system in animals
4
Q
what do mass transport systems ensure
A
efficient movement of substances throughout the organism
5
Q
what is haemoglobin an important part of?
A
the circulatory system
6
Q
where is human haemoglobin found?
A
human haemoglobin is found in red blood cells
7
Q
what is the role of haemoglobin
A
to carry oxygen around the body
8
Q
what can haemoglobin be abbreviated to?
A
Hb
9
Q
what structure does haemoglobin have
A
haemoglobin is a large protein with a quaternary structure
10
Q
what is haemoglobin made up of
A
it is made up of 4 polypeptide chains (2 alpha chains and 2 beta chains)
11
Q
what does each polypeptide chain in haemoglobin have?
A
each chain has a haem group containing a Fe2+ ion and gives haemoglobin its red colour
12
Q
how many molecules of oxygen can a human haemoglobin carry?
A
each molecule of human haemoglobin can carry 4 oxygen molecules
13
Q
formation of oxyhaemoglobin
A
in the lungs, oxygen joins to haemoglobin in red blood cells to form oxyhaemoglobin
14
Q
is the formation of oxyhaemoglobin a reversible or irreversible reaction?
A
a reversible reaction, near the body cells oxygen leaves oxyhaemoglobin and it turns back to haemoglobin
15
Q
association/loading
A
when an oxygen molecule joins to haemoglobin it’s referred to as association/loading
16
Q
dissociation/unloading
A
when oxygen leaves haemoglobin it’s referred to as dissociation/unloading
17
Q
equation for association/dissociation
A
Hb + (4) O2 = Hb,O8
reversible reaction
18
Q
what is affinity for oxygen
A
affinity for oxygen means the tendency a molecule has to bind with oxygen
19
Q
can haemoglobin’s affinity vary?
A
haemoglobin’s affinity for oxygen varies depending on the conditions it’s in
20
Q
what is one of the conditions which affects haemoglobin’s affinity?
A
one of the conditions affecting this is partial pressure of oxygen
21
Q
how can partial pressure of oxygen be written
A
pO2
22
Q
what is partial pressure of oxygen a measure of
A
partial pressure of oxygen is a measure of oxygen concentration
23
Q
what does a higher partial pressure of oxygen mean
A
the greater the concentration of dissolved oxygen in cells, the higher the partial pressure of oxygen
24
Q
relationship between partial pressure of oxygen and haemoglobin’s affinity
A
as partial pressure of oxygen increases, so does haemoglobin’s affinity for oxygen
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PO2 and loading
oxygen loads onto haemoglobin to form oxyhaemoglobin where there's a high PO2
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PO2 and unloading
oxyhaemoglobin unloads its oxygen where there's a lower PO2
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example of loading in the body
oxygen enters blood capillaries at alveoli in lungs where there is a high PO2 so oxygen loads onto haemoglobin to form oxyhaemoglobin
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example of unloading in the body
when cells respire, they use up oxygen (lowers PO2). red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads its oxygen. haemoglobin returns to the lungs to pick up more oxygen
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what does an oxygen dissociation curve show
an oxygen dissociation curve shows how saturated the haemoglobin is with oxygen at any given partial pressure
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affinity for haemoglobin and saturation of haemoglobin
affinity of haemoglobin for oxygen affects how saturated the haemoglobin is
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high PO2 and how this affects affinity and saturation
high PO2 e.g. lungs = haemoglobin has high affinity for O = high saturation of O
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low PO2 and how this affects affinity and saturation
low PO2 e.g. respiring tissues = haemoglobin has low affinity for O = low saturation of O
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why is a dissociation curve S shaped
saturation of haemoglobin can also affect the affinity
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what happens after haemoglobin combines with the first O2 molecule
when haemoglobin combines with the first O2 molecule, its shape alters which makes it easier for other O2 molecules to join
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what happens when haemoglobin becomes more saturated
as haemoglobin becomes more saturated, it gets harder for more oxygen molecules to join
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shape of dissociation curve
steepness
curve has steep bit in middle (really easy for oxygen molecules to join
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shape of dissociation curve
shallowness
curve is shallow at both ends as it is hard for oxygen molecules to join
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how does a change in PO2 have an impact when the curve is steep
when curve is steep, small change in PO2 causes a big change in the amount of oxygen carried by the haemoglobin
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what can partial pressure of carbon dioxide be written as
pCO2
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what is pCO2 a measure of
pCO2 is a measure of the concentration of CO2 in a cell
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does pCO2 affect oxygen unloading?
pCO2 affects oxygen unloading
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what does haemoglobin do at a higher pCO2
haemoglobin gives up its oxygen more readily at a high pCO2
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what do cells produce when they respire
when cells respire they produce CO2 which raises the pCO2
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what happens when pCO2 is raised
this increases the rate of oxygen unloading (rate at which oxyhaemoglobin dissociates to form haemoglobin and oxygen)
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what happens to the dissociation curve at a higher pCO2
dissociation curve shifts to the right but stays the same shape. saturation of blood with oxygen is lower for a given pO2, meaning that more oxygen is being released - Bohr effect
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is having a particular type of haemoglobin an adaptation?
having a particular type of haemoglobin is an adaptation that helps the organism to survive in a particular environment
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haemoglobin in low oxygen environments
organisms living in environments with low concentrations of oxygen have haemoglobin with a higher affinity for oxygen in comparison to human haemoglobin
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why is haemoglobin adapted this way for low oxygen environments
isn't much oxygen available so haemoglobin has to be very good at loading any available oxygen
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how is the dissociation curve affected for low oxygen environments
dissociation curve of haemoglobin is the shifted to the left of the human one
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give an example of an organism that lives in a low oxygen environment
lugworm - lives in burrows beneath sand do low oxygen concentration
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haemoglobin for high activity levels
very active organisms with a high oxygen demand have haemoglobin with a lower affinity for oxygen than human haemoglobin
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why is haemoglobin adapted this way for high activity levels
they need their haemoglobin to easily unload oxygen, so that it's available for them to use
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how is the dissociation curve affected for high activity levels
dissociation curve of haemoglobin is to the right of the human one
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give an example of an organism that has high activity levels
hawk = high respirator rate (as very active) and lives where there's plenty of oxygen
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smaller mammals sa:v ratio
small mammals tend to have a higher sa:v ratio than larger mammals
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due to smaller mammals sa:v ratio what does this mean about their metabolic rate/oxygen demand
this means they lose heat quickly so have a high metabolic rate to keep them warm so they have a high oxygen demand
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smaller mammals oxygen affinity as a result of their oxygen demand
haemoglobin with a lower affinity for oxygen than human haemoglobin
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why do smaller mammals have this affinity for oxygen
they need their haemoglobin to easily unload oxygen to meet their high oxygen demand
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smaller mammals dissociation curve
dissociation curve of haemoglobin is to the right of the human one
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where does the right side of the blood pump blood to
right side pumps deoxygenated blood to the lungs
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where does the left side pump blood to
left side pumps oxygenated blood to the whole body
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how is the left ventricle adapted
left ventricle of the heart has thicker and more muscular walls than the right ventricle
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why does the left ventricle have this adaptation
allows it to contract more powerfully and pump blood all the way around the body
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as a result of right ventricle being less muscular what does this mean
right ventricle is less muscular so its contractions are only powerful enough to pump blood to the lungs
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adaptation of ventricles
ventricles have thicker walls than the atria
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why do ventricles have this adaptation
they can push blood out of the heart
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why do atria have thinner walls than ventricles
atria just need to push blood a short distance into the ventricles
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what do atrioventricular valves link the atria to
atrioventricular valves link the atria to the ventricles
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what do atrioventricular valves stop
stop blood flowing back into the atria when the ventricles contract
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what do the semi lunar valves link the ventricles to
semi lunar valves link the ventricles to the pulmonary artery and the aorta
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what do the semi lunar valves stop
stop blood flowing back into the heart when the ventricles contract
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what do the cords do
cords attach the atrioventricular valves to the ventricles to stop them being forced up into the atria when the ventricles contract
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heart valves
do valves only open one way
the valves only open one way
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heart valves
what controls whether they are open or closed
whether they are open or closed depends on the relative pressure of the heart chambers
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heart valves
what causes them to open
if there is higher pressure behind a valve, it is forced open
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heart valves
what causes them to close
if pressure is higher in front of the valve then it is forced shut
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how can blood flow be described in the heart
flow of blood is unidirectional - only flows in 1 direction
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HEART DISSECTION
step 1
1. put on a lab coat and gloves
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HEART DISSECTION
step 2
2. place the heart on the dissecting tray
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HEART DISSECTION
step 3
3. try to identify the 4 main vessels attached to it ( arteries are thick/rubbery, veins are thinner)
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HEART DISSECTION
step 4
4. identify right and left atria , right and left ventricles and coronary arteries
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HEART DISSECTION
step 5
5. cut open by the left and right ventricles with a scalpel and notice the difference in thickness of the ventricle walls
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HEART DISSECTION
step 6
6. cut open the atria, , atria walls are thinner than ventricle walls
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HEART DISSECTION
step 7
7. find the atrioventricular valves and semi-lunar valves
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HEART DISSECTION
step 8
8. wash hands and disinfect workspace
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stages of cardiac cycle
1. ventricles relax, atria contract
2. ventricles contract, atria relax
3. ventricles relax, atria relax
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what is cardiac contraction called
systole
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what is cardiac relaxation called
diastole
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Cardiac cycle- ventricles relax, atria contract:
step 1. how are the ventricles
1.ventricles are relaxed
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Cardiac cycle- ventricles relax, atria contract:
step 2. what do the atria do, what does this cause in terms of pressure
2. atria contract, decreasing the volume of the chambers and increasing the pressure inside the chambers
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Cardiac cycle- ventricles relax, atria contract:
step 3. where does this push blood
3. this pushes blood into the ventricles
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Cardiac cycle- ventricles relax, atria contract:
step 4. what now happens to volume/pressure
4. is a slight increase in ventricular pressure and chamber volume as the ventricles receive the ejected blood from the contracting atria
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Cardiac cycle- ventricles contract, atria relax:
step 1. what do the atria do
1. the atria relax
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Cardiac cycle- ventricles contract, atria relax:
step 2. what do the ventricles do
2. ventricles contract, decreasing their volume and increasing their pressure
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Cardiac cycle- ventricles contract, atria relax:
step 3. where is pressure now higher
3. pressure now higher in the ventricles than the atria
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Cardiac cycle- ventricles contract, atria relax:
step 4. what does this pressure difference cause
4. forces he atrioventricular valves shut to prevent backflow
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Cardiac cycle- ventricles contract, atria relax:
step 5. what is the pressure in the ventricles also higher than
5. pressure in the ventricles is also higher than in the aorta and pulmonary artery
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Cardiac cycle- ventricles contract, atria relax:
step 6. where is blood forced out and why
6. forces open the semi lunar valves and blood is forced out into these arteries
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Cardiac cycle- ventricles relax, atria relax:
step 1. state of atria and ventricles
1. ventricles and atria both relax
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Cardiac cycle- ventricles contract, atria relax:
step 2. where is their higher pressure and what does this cause
2. higher pressure in the pulmonary artery and the aorta closes SL valve to prevent back-flow into the ventricles
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Cardiac cycle- ventricles contract, atria relax:
step 3. where does blood return to
3. blood returns to the heart and the atria fill again due to the higher pressure in the vena cava and pulmonary vein
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Cardiac cycle- ventricles contract, atria relax:
step 4. pressure of atria
4. this starts to increase the pressure of the atria
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Cardiac cycle- ventricles contract, atria relax:
step 5. ventricle pressure
5. as ventricles relax, their pressure falls below pressure of atria
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Cardiac cycle- ventricles contract, atria relax:
step 6. what opens
6. AV valves open
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Cardiac cycle- ventricles contract, atria relax:
step 7. how does blood flow
7. allows blood to flow passively ( without being pushed by atrial contraction) into the ventricles from the atria
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Cardiac cycle- ventricles contract, atria relax:
step 8. what does the atria do
8. atria contracts, whole process starts again
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what is cardiac output
volume of blood pumped by the heat per minute
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what is cardiac output measured in
cm^3 min^-1
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equation for cardiac output
cardiac output = stroke volume * heart rate
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what is heart rate
number of beats per minute (bpm)
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what is stroke volume
volume of blood pumped in each heartbeat (cm^3)
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multicellular organisms sa:v ratio
multicellular organisms have low sa:v ratio
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what do multicellular organisms need as a result of their sa:v ratio
need specialised mass transport system to carry raw materials from specialised exchange organs to their body cells (circulatory system)
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what is the circulatory system made up of
made up of the heart and blood vessels
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circulatory system: what does the heart pump blood through
heart pumps blood through blood vessels
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name types of blood vessels
- arteries
- capillaries
- arterioles
- veins
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pulmonary artery:
where does it carry blood from and to
carries blood from the heart to the lungs
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pulmonary vein:
where does it carry blood from and to
carries blood from the lungs to the heart
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aorta:
where does it carry blood from and to
carries blood from the heart to the body
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vena cava:
where does it carry blood from and to
carries blood from the body to the heart
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renal artery:
where does it carry blood from and to
carries blood from the body to the kidneys
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renal vein:
where does it carry blood from and to
carries blood from the kidneys to the vena cava
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what does blood transport
- respiratory gases
- products of digestion
- metabolic wastes
- hormones
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where does one circuit take blood
one circuit takes blood from the heart to the lungs, then back to the heart
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where does the other circuit take blood
other loop takes blood around the rest of the body,
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how many times does blood have to go through the heart to complete one full circuit of the body
blood has to go through the heart twice to complete one full circuit of the body
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does the heart have its own blood supply
heart has its own blood supply- left and right coronary arteries
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ARTERIES
where do arteries carry blood from/to
arteries carry blood from the heart to the rest of the body
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ARTERIES
artery walls
their walls are thick/muscular, have elastic tissue to stretch and recoil as the heart beats, which helps maintain the high pressure
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ARTERIES
inner lining
inner lining (endothelium) is folded, allowing the artery to stretch - also helps it to maintain high presssure
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ARTERIES
do they carry oxygenated or deoxygenated blood
all arteries carry oxygenated blood except pulmonary arteries
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ARTERIES
where do pulmonary arteries take blood to
pulmonary arteries take deoxygenated blood to the lungs
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ARTERIOLES
what do arteries divide into
arteries divide into smaller vessels called arterioles
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ARTERIOLES
what do these form throughout the body
these form a network throughout the body
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ARTERIOLES
what is blood directed by
blood is directed to different areas of demand in the body by muscles inside the arterioles
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ARTERIOLES
how do they control blood flow
arterioles contract to restrict blood flow/relax to allow full blood flow
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VEINS
where do veins take blood to, under high or low pressure
veins take blood back to the heart under low pressure
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VEINS
lumen, elastic/muscle tissue
have a wider lumen than equivalent arteries, with very little elastic or muscle tissue
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VEINS
valves
veins contain valves to stop the blood flowing backwards
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VEINS
what is blood flow through the veins helped by
blood flow through veins is helped by contraction of the body muscles surrounding them
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VEINS
do they carry oxygenated or deoxygenated blood
all veins carry deoxygenated blood (as oxygen has been used up by body cells)
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VEINS
pulmonary veins
pulmonary veins however carry oxygenated blood to the heart from the lungs
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CAPILLARIES
what do arterioles branch into
arterioles branch into capillaries, which are the smallest of the blood vessels
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CAPILLARIES
what are they well adapted for and why
substances e.g. glucose and oxygen are exchanged between cells and capillaries, so they are adapted for efficient diffusion
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CAPILLARIES
diffusion pathway
always found very near in exchange tissue (e.g. alveoli in the lungs), so there's a short diffusion pathway
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CAPILLARIES
how thick are the walls
walls are only one cell thick = shortens diffusion pathway
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CAPILLARIES
surface area
large number of capillaries to increase SA for exchange
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CAPILLARIES
capillary beds
networks of capillaries in tissue are called capillary beds
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TISSUE FLUID
1. what is tissue fluid
1.tissue fluid is the fluid that surrounds cells in tissues
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TISSUE FLUID
2. what is tissue fluid made from
2.made from small molecules that leave the blood plasma e.g. oxygen, water and nutrients
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TISSUE FLUID
3. what doesn't tissue fluid contain
3. red blood cells or big proteins (too large to be pushed out through the capillary walls)
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TISSUE FLUID
4. what do cells take in from tissue fluid
4. cells take in oxygen and nutrients from the tissue fluid
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TISSUE FLUID
5. what do cells release into tissue fluid
5. release metabolic waste into it
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TISSUE FLUID
6. pressure filtration
6. in a capillary bed, substances move out of the capillaries, into the tissue fluid by pressure filtration
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TISSUE FLUID
7. hydrostatic pressure at the start of the capillary bed
7. at the start of the capillary bed, nearest the arteries, the hydrostatic (liquid) pressure inside the capillaries is greater than the hydrostatic pressure in the tissue fluid
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TISSUE FLUID
8. what does this difference in hydrostatic pressure at the start of the capillary bed cause
8. difference in hydrostatic pressure means an overall outward pressure forces fluid out of the capillaries and into the spaces around the cells, forming tissue fluid
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TISSUE FLUID
9. what happens as fluid leaves
9. as fluid leaves, the hydrostatic pressure reduces in the capillaries - so the hydrostatic pressure is much lower at the venule end of the capillary bed (end nearest to the veins)
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TISSUE FLUID
10. what happens due to fluid loss
10. due to fluid loss, an increasing concentration of plasma proteins (which don't leave the capillaries ), the water potential at the venule end of the capillary bed is lower than the water potential in the tissue fluid
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TISSUE FLUID
11. what happens as a result of the water potential at the venule end of the capillary bed is lower than the water potential in the tissue fluid
11. this means that some water re-enters the capillaries from the tissue fluid at the venule end by osmosis
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TISSUE FLUID
12. what happens to any excess tissue fluid
12. any excess tissue fluid is drained into the lymphatic system which transports this excess fluid from the tissues and passes it back into the circulatory system
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TISSUE FLUID
13. what is the lymphatic system
13. network of tubes that acts a bit like a drain
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what are cardiovascular diseases
diseases associated with the heart and blood vessels
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examples of cardiovascular diseases
- thrombosis
- aneurysms
- myocardial infarction
- coronary heart disease
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what do most cardiovascular diseases start with
atheroma formation
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when does coronary heart disease occur
occurs when the coronary arteries have lots of atheromas in them, which restricts blood flow to the heart muscle
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what can coronary heart disease lead to
myocardial infarction
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ATHEROMA FORMATION
1. what is the wall of the artery made up of
1. artery wall is made up of several layers
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ATHEROMA FORMATION
2. what is the endothelium in the artery usually like
2.endothelium (inner lining) is usually smooth and unbroken
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ATHEROMA FORMATION
3. what happens if the endothelium of the artery becomes damaged
3. if damage occurs to the endothelium, white blood cells (mostly macrophages) and lipids (fat) from the blood, clump together under the lining to form fatty streaks
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ATHEROMA FORMATION
4. what is one way the endothelium of the artery can become damaged
4. by high blood pressure
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ATHEROMA FORMATION
5. what happens over time
5. over time, more white blood cells, lipids and connective tissue build up and harden to form a fibrous plaque (atheroma)
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ATHEROMA FORMATION
6. what do atheromas block and what does this cause
6. this plaque partially blocks the lumen of the artery and restricts blood flow, which causes blood pressure to increase
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ANEURYSM
1. what is an aneurysm
1. an aneurysm is a balloon like swelling of the artery
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ANEURYSM
2. what does an aneurysm start with the formation of
2. it starts with the formation of atheromas
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ANEURYSM
3. what do these atheromas do
3. atheromas plaque damage and weaken arteries, and narrow arteries, increasing blood pressure
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ANEURYSM
4. what happens when blood travels through this weakened artery
4. when blood travels through a weakened artery at high pressure, it may push the inner layers of the artery through the outer elastic layer to form an aneurysm
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ANEURYSM
5. can aneurysms burst
5. aneurysms may burst, causing a haemorrhage (bleeding)
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THROMBOSIS
1. what is thrombosis
1. the formation of a blood clot
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THROMBOSIS
2. what do they start with the formation of
2. starts with the formation of atheromas
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THROMBOSIS
3. what can an atheroma plaque rupture
3. an atheroma plaque can rupture the endothelium of an artery
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THROMBOSIS
4. what does this rupture damage
4. this damages the artery wall and leaves a rough surface
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THROMBOSIS
5. what happens at the site of damage
5. platelets and fibrin accumulate at the site of damage and from a blood clot (a thrombus)
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THROMBOSIS
6. what can this blood clot do
6. blood clot can cause a complete blockage of the artery , or it can become dislodged and block a blood vessel elsewhere in the body
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THROMBOSIS
7. what can debris from the rupture cause
7. debris from the rupture can cause another blood clot to form further down the artery
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MYOCARDIAL INFARCTION:
1. what is this
1. a heart attack
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MYOCARDIAL INFARCTION:
2. what supplies blood to the heart muscle
2. heart muscle is supplied with blood by the coronary arteries
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MYOCARDIAL INFARCTION:
3, why does heart muscle need a supply of blood
3. blood contains oxygen needed by heart muscle cells to carry out respiration)
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MYOCARDIAL INFARCTION:
4. what happens if a coronary artery becomes blocked
4. if a coronary artery becomes blocked e.g. by a blood clot an area of the heart muscle will be cut off from its blood supply and receive no oxygen
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MYOCARDIAL INFARCTION:
5. what happens as a result of coronary artery being blocked
5. causes a myocardial infarction
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MYOCARDIAL INFARCTION:
6. what can a heart attack cause
6. heart attack can cause damage and death of the heart muscle
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MYOCARDIAL INFARCTION:
7. symptoms
7. - pain in the chest and upper
body
- shortness of breath
- sweating
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MYOCARDIAL INFARCTION:
8. wat happens if large areas of the heart muscle are affected
8, if large areas of the heart muscle are affected complete heart failure can occur which is often fatal
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risk factors for cardiovascular disease
- high blood pressure
- smoking
- high blood cholesterol and poor diet
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HIGH BLOOD PRESSURE:
1. what does high bp increase the risk of
1. high bp increases the risk of damage to the artery walls
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HIGH BLOOD PRESSURE:
2. what do damaged walls have an increased risk of
2, damaged walls have an increased risk of atheroma formation, causing a further increase in bp
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HIGH BLOOD CHOLESTEROL AND POOR DIET
1. what does high blood cholesterol increase the risk of
1. if blood cholesterol is high (above 240mg per 100cm^3) then the risk of cardiovascular disease is increased
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HIGH BLOOD CHOLESTEROL AND POOR DIET
2. why does high blood cholesterol increase the risk of cardiovascular disease
2. cholesterol is one of the main constituents of the fatty deposits that form atheromas
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HIGH BLOOD CHOLESTEROL AND POOR DIET
3. diet and the effects
3. high fat diet = high blood cholesterol
diet high in salt = high bp
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what substances in cigarette smoke increase the risk of a heart attack
nicotine and carbon monoxide
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what does carbon monoxide combine with
carbon monoxide combines with haemoglobin and reduces the amount of oxygen transported in the blood
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how does carbon monoxide increase risk of heart attack
reduces amount of oxygen available to tissues. if the heart muscle doesn't receive enough oxygen it can lead to a heart attack
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how else does smoking increase the risk of atheroma formation
smoking decreases the amount of antioxidants in the blood (important for protecting cells from damage) so cell damage in the coronary artery walls is more likely which can lead to atheroma formation
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role of the xylem
xylem tissue transports water and mineral ions in solution. these substances move up the plant from the roots to the leaves
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role of the phloem
phloem tissue transports organic substances like sugars (also in solution) both up and down the plant
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what direction does water move up a plant
water moves up a plant against the force of gravity, from roots to leaves
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cohesion-tension theory of water transport:
1. where does water evaporate from
1. water evaporates from the leaves at the top of the xylem. this is a process called transpiration
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cohesion-tension theory of water transport:
2. what does this transpiration cause
2. this creates tension (suction), which pulls more water into the leaf
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cohesion-tension theory of water transport:
3. where does the whole column of water in the xylem move
3. water molecules are cohesive (they stick together) so when some are pulled into the leaf others follow. this means the whole column of water in the xylem, from the leaves down to the roots, moves upwards
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cohesion-tension theory of water transport:
4. where does the water then enter
4. water then enters the stem through the roots
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transpiration:
1. what is transpiration
1. transpiration is the evaporation of water from a plant's surface, especially the leaves
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transpiration:
2. where does water evaporate from and then accumulate
2. water evaporates from the moist cell walls and accumulates in the spaces between cells in the leaf
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transpiration:
3. where does the water move after the stomata opens
3. when the stomata open, water moves out of the leaf down the water potential gradient
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transpiration:
4. why does water move out of the leaf down the water potential gradient
4. as there is more water inside the leaf than in the air outside
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what are the factors affecting transpiration rate
- light intensity
- temperature
- humidity
- wind
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correlation between light intensity and rate of transpiration
higher light intensity = faster rate of transpiration (positive correlation)
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explanation for correlation between light intensity and rate of transpiration
the stomata open when it gets light to let carbon dioxide in for photosynthesis, when it's dark the stomata are usually closed so there is little transpiration
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correlation between temperature and rate of transpiration
high temperature -= faster rate of transpiration (positive correlation)
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explanation for correlation between temperature and rate of transpiration (part one)
warmer water molecules have more energy so they evaporate from the cells inside the leaf faster
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explanation for correlation between temperature and rate of transpiration (part two)
this increases the water potential gradient between the inside and outside of the leaf, making the water diffuse out of the leaf faster
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correlation between humidity and rate of transpiration
lower humidity = faster rate of transpiration (negative correlation)
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explanation for correlation between humidity and rate of transpiration
if the air around the plant is dry, the water potential gradient between the leaf and the air is increased, which increases transpiration rate
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correlation between wind and rate of transpiration
windier it is, the faster the transpiration rate (positive correlation)
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explanation for correlation between wind and rate of transpiration
lots of air movement blows away water molecules from around the stomata, increasing water potential gradient, increasing rate of transpiration
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what is a potometer used for
potometer is used to estimate transpiration rates
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using a potometer
step 1
1. cut a shoot underwater to prevent air from entering the xylem. cut it at a slant to increase the SA available for water uptake
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using a potometer
step 2
2. assemble the potometer under the water and insert the shoot with the apparatus still under the water, so no air can enter
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using a potometer
step 3
3. remove the apparatus from the water but keep the end of the capillary tube submerged in a beaker of water
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using a potometer
step 4
4. check that the apparatus is watertight and airtight
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using a potometer
step 5
5. dry the leaves, allow time for the shoot to acclimatise and then shut the tap
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using a potometer
step 6
6. remove the end of the capillary tube from the beaker of water until 1 air bubble has formed, then put the end of the tube back into the water
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using a potometer
step 7
7. record the starting position of the air bubble
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using a potometer
step 8
8. start a stopwatch and record the distance moved by the bubble per unit time. rate of air bubble movement is an estimate of the transpiration rate
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using a potometer
step 9
9. only change one variable at a time, all other conditions must be kept constant
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what are solutes
dissolved substances
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what is the phloem formed from
phloem is formed from cells arranged in tubes
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important cell types in phloem tissue
sieve tube elements and companion cells
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sieve tube elements
sieve tube elements are living cells that form the tube for transporting solutes. they have no nucleus and few organelles
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companion cells
there is a companion cell for each sieve tube element. they carry out living functions for sieve cells e.g. providing the energy needed for active transport of solutes
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what is translocation
translocation is the movement of solutes (e.g. amino acids and sugars like sucrose) to where they're needed in a plant
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what are solutes sometimes called
assimilates
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does translocation require energy and where does it happen
it is an energy requiring process that happens in the phloem
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where does translocation move solutes from and to
translocation moves solutes from sources to sinks
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sources
the source is where assimilates are produced (so are at a high concentration here)
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sinks
the sink is where assimilates are used up (so are are at a lower concentration here)
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where is the source for sucrose usually in plants
source for sucrose is usually the leaves
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where is the sink usually in plants
sinks are the other parts of the plant , especially the food storage organs and the meristems in the roots, stems and leaves
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what do enzymes maintain
enzymes maintain a concentration gradient from the source to the sink
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how do enzymes maintain this concentration gradient
by breaking them down or making them into something else
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what does this maintained concentration gradient result in
this makes sure there is always a lower concentration at the sink than at the source
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MASS FLOW HYPOTHYSIS
source
step one
1. active transport is used to actively load the solutes (e.g. sucrose from photosynthesis) from the companion cells into the sieve tubes
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MASS FLOW HYPOTHYSIS
source
step two
2. so water enters the tubes by osmosis from the xylem and companion cells
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MASS FLOW HYPOTHYSIS
source
step three
3. this creates a high pressure inside the sieve tubes at the source end of the phloem
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MASS FLOW HYPOTHYSIS
sink
step one
1. at the sink end, solutes are removed from the phloem to be used up
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MASS FLOW HYPOTHYSIS
sink
step two
2. this increases the water potential inside the sieve tubes, so water also leaves the tubes by osmosis
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MASS FLOW HYPOTHYSIS
sink
step three
3. this lowers the pressure inside the sieve tubes
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MASS FLOW HYPOTHYSIS
flow
step one
1. the result is a pressure gradient from the source end to the sink end
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MASS FLOW HYPOTHYSIS
flow
step two
2. this gradient pushes solutes along the sieve tubes towards the sink
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MASS FLOW HYPOTHYSIS
flow
step three
3. when they reach the sink the solutes will be used (e.g. in respiration) or stored (e.g. as starch)
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MASS FLOW HYPOTHYSIS
flow
step four
4. the higher the concentration of sucrose at the source, the higher the rate of translocation
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