substance exchange - mass transport Flashcards
What is the name given to haemoglobin that has bound to oxygen?
What is the name given to haemoglobin that has bound to oxygen?
oxyhaemoglobin
One haemoglobin molecule contains …. The haem groups contain …
One haemoglobin molecule contains four haem groups. The haem groups contain an iron ion which is what makes haemoglobin red.
Dissociation
Dissociation
When the red blood cells reach the tissues in the body (e.g. muscle cells), oxygen is released from the oxyhaemoglobin in a process called dissociation.
Haem groups
Each polypeptide chain in a haemoglobin molecule has …
A haem group is …
The haem groups contain an iron ion.
The iron ion is what …
Haem groups
Each polypeptide chain in a haemoglobin molecule has a haem group.
A haem group is a prosthetic group that is attached to the protein.
The haem groups contain an iron ion.
The iron ion is what makes haemoglobin red.
Affinity
Haemoglobin has a high ___ (attraction) for oxygen.
When red blood cells reach the lungs, …
When oxygen binds to haemoglobin, ___ is formed.
Affinity
Haemoglobin has a high affinity (attraction) for oxygen.
When red blood cells reach the lungs, oxygen diffuses into the red blood cells and binds to haemoglobin.
Four molecules of oxygen bind to one molecule of haemoglobin.
When oxygen binds to haemoglobin, oxyhaemoglobin is formed.
Partial pressure
Oxygen partial pressure (pO2) is …
Carbon dioxide partial pressure (pCO2) is …
pO2 is important in determining …
Partial pressure
Oxygen partial pressure (pO2) is the concentration of oxygen in the cells.
Carbon dioxide partial pressure (pCO2) is the concentration of carbon dioxide in the cells.
pO2 is important in determining whether oxygen binds to haemoglobin.
Affinity
pO2 determines …
If pO2 is high, haemoglobin ..
If pO2 is low, haemoglobin …
Affinity
pO2 determines the affinity of haemoglobin for oxygen.
If pO2 is high, haemoglobin has a high affinity for oxygen and oxygen binds to haemoglobin.
If pO2 is low, haemoglobin has a low affinity for oxygen and oxygen dissociates from haemoglobin.
Transport of oxygen
The effect of pO2 on the affinity of haemoglobin allows …
This allows …
Transport of oxygen
The effect of pO2 on the affinity of haemoglobin allows oxygen to be transported from the lungs (where there is lots of oxygen) to the respiring tissues (where oxygen is limited).
This allows oxygen to be transported to the cells where oxygen is needed most.
Animals living at high altitudes have haemoglobin which has ….
This is an advantage because …
___ also have haemoglobin with a high affinity for oxygen.
Animals living at high altitudes have haemoglobin which has a high affinity for oxygen.
This is an advantage because the air at higher altitudes has a much lower partial pressure than at sea level.
Birds also have haemoglobin with a high affinity for oxygen.
High metabolic rate
Animals with high metabolic rates have haemoglobin …
This allows …
High metabolic rate
Animals with high metabolic rates have haemoglobin that dissociates with oxygen very easily.
This allows oxygen to be quickly and easily supplied to the cells for use in respiration.
What is the impact on haemoglobin when the first molecule of oxygen binds?
What is the impact on haemoglobin when the first molecule of oxygen binds?
O2 BINDS MORE EASILY
Dissociation Curves
Dissociation Curves
The relationship between the percentage saturation of haemoglobin and oxygen partial pressure of the surrounding tissues can be shown in a dissociation curve.
Low pO2
When partial pressure is low, …
The percentage saturation of haemoglobin is low COZ ..
Low pO2
When partial pressure is low, haemoglobin has a low affinity for oxygen.
The percentage saturation of haemoglobin is low because oxygen dissociates from the haemoglobin.
Increasing pO2
As pO2 increases, …
When the first molecule of O2 binds to haemoglobin, ..
The change in shape allows …
The percentage saturation…
Increasing pO2
As pO2 increases, affinity of haemoglobin for oxygen increases slightly.
When the first molecule of O2 binds to haemoglobin, the protein undergoes a conformational change.
The change in shape allows the other O2 molecules to bind to haemoglobin more easily.
The percentage saturation of haemoglobin increases quickly.
Plateau in percentage saturation
As more molecules of O2 bind to haemoglobin, …
The percentage saturation of haemoglobin …
Plateau in percentage saturation
As more molecules of O2 bind to haemoglobin, it becomes more difficult for more O2 molecules to bind.
The percentage saturation of haemoglobin begins to plateau.
S-shaped curve
The increasing affinity of haemoglobin …
The S-shaped curve is called …
S-shaped curve
The increasing affinity of haemoglobin with increasing pO2 in this way creates an S-shaped curve.
The S-shaped curve is called the dissociation curve.
High pCO2
Respiring cells use … and produce …
The respiring cells have low ___ and high ___.
When pCO2 is high, …
High pCO2
Respiring cells use oxygen in respiration and produce carbon dioxide.
The respiring cells have low pO2 and high pCO2.
When pCO2 is high, the rate of oxygen dissociation increases.
Bohr effect
The increased dissociation of oxygen causes …
… means that oxygen will dissociate from haemoglobin at a lower pO2 than normal.
This is called …
Bohr effect
The increased dissociation of oxygen causes a shift in the oxyhaemoglobin dissociation curve to the right.
The shift in the dissociation curve means that oxygen will dissociate from haemoglobin at a lower pO2 than normal.
This is called the Bohr effect.
How does a high pCO2 impact haemoglobin affinity for oxygen?
How does a high pCO2 impact haemoglobin affinity for oxygen?
decreases affinity
The heart is the centre of …
Mammals have a double circulatory system. This means …
Deoxygenated blood is pumped to …
Oxygenated blood is pumped …
The heart is the centre of the circulatory system.
Mammals have a double circulatory system. This means blood flows through the heart twice in one circuit.
Deoxygenated blood is pumped to the lungs.
Oxygenated blood is pumped around the body.
Coronary arteries
The heart is a muscle that is constantly contracting and relaxing.
The heart muscle needs a constant supply of oxygen for ____.
The coronary arteries supply ….
Coronary arteries
The heart is a muscle that is constantly contracting and relaxing.
The heart muscle needs a constant supply of oxygen for respiration.
The coronary arteries supply blood to the heart.
Pulmonary artery & vein
… is pumped out of the heart to the lungs via the pulmonary artery.
Oxygen diffuses into …
Oxygenated blood flows …
Pulmonary artery & vein
Deoxygenated blood is pumped out of the heart to the lungs via the pulmonary artery.
Oxygen diffuses into the deoxygenated blood in the lungs and the blood becomes oxygenated.
Oxygenated blood flows into the heart from the lungs via the pulmonary vein.
Aorta & vena cava
Oxygenated blood is pumped out of the heart around the body via the aorta.
Blood in the aorta is very high pressure to ensure the blood can be pumped to all the tissues in the body.
Oxygen dissociates from the blood at respiring cells in the body and the blood becomes deoxygenated.
Deoxygenated blood flows into the heart from the body via the vena cava.
Aorta & vena cava
Oxygenated blood is pumped out of the heart around the body via the aorta.
Blood in the aorta is very high pressure to ensure the blood can be pumped to all the tissues in the body.
Oxygen dissociates from the blood at respiring cells in the body and the blood becomes deoxygenated.
Deoxygenated blood flows into the heart from the body via the vena cava.
Arteries Away
vEins rEturn
Arteries Away
vEins rEturn
flow of blood
flow of blood
the blood is going to move from the right atrium thru the right av valve and into the right ventricle
the its gonna move out thru the semilunar valve into the pulmonary artery (cos we’re moving away from the heart)
from the PA (PULMONARY ARTERY) we’re going to the lungs
in the lungs we pick up oxygen and were gonna return to the heart down the pulmonary vein
from there were gonna enter the left side of the heart
blood is gonna enter thru the left atrium thru the left av valve and into the left ventricle
and from there we r gonna pass thru that semilunar valve and into the aorta
and the aorta is gonna pump the blood right around the body where its gonna lose its oxygen and end up back at the vena cava
from there we go back into the right atrium and the cycle repeats
flow of blood order
flow of blood order
right atrium right ventricle pulmonary artery lungs pulmonary vein left atrium left ventricle aorta body vena cava
what is the point of valves
valves prevent back flow
whats the point of AV valves
whats the point of AV valves
AV valves prevent blood from flowing back into atria when ventricles contract
whats the point of semilunar valves
whats the point of semilunar valves
semilunar valves stop blood from flowing from arteries back into ventricles
blood wants to move from …
when a chamber contracts, …
so blood could either move onto the next part of the heart or backwards: …
blood wants to move from high pressure to low pressure
when a chamber contracts, the pressure increases
so blood could either move onto the next part of the heart or backwards: both r at low pressure
valves prevent back flow
Vena cava
Renal
artery
Pulmonary
vein
Aorta
Coronary
arteries
Vena
cava
The blood vessel that carries deoxygenated blood from the body into the heart.
Renal
artery
The blood vessel that oxygenated blood flows through to enter the kidneys.
Pulmonary
vein
The blood vessel that carries oxygenated blood from the lungs to the heart.
Aorta
The blood vessel that oxygenated blood flows out of the heart through and to the rest of the body.
Coronary
arteries
The blood vessels that supply blood to the heart.
the cardiac cycle
1) Atrial contraction
the cardiac cycle
1) Atrial contraction
Blood from the lungs flows into the left atrium and blood from the body flows into the right atrium simultaneously.
The atria contract, increasing the pressure in the atria.
The blood in the atria is forced into the ventricles.
The ventricles are relaxed and fill with blood.
the cardiac cycle
2) Ventricular contraction
the cardiac cycle
2) Ventricular contraction
The atria relax and the ventricles start to contract.
Contraction of the ventricles causes the pressure inside the ventricles to increase.
The pressure shuts the atrioventricular valves so that blood does not flow back into the atria.
The blood in the ventricles is forced out of the ventricles and out of the heart through the pulmonary artery or the aorta.
the cardiac cycle
3) Relaxation
the cardiac cycle
3) Relaxation
The blood in the pulmonary artery and the aorta is at high pressure. -The pressure shuts the semi-lunar valves so that blood does not flow back into the ventricles.
Both the ventricles and the atria relax and the atrioventricular valves reopen.
Blood flows into the ventricles and the atria from the pulmonary vein and vena cava.
the cardiac cycle
4) cycle repeats
the cardiac cycle
Right atrium
Deoxygenated blood flows into ..
The vein that pumps deoxygenated blood into the right atrium is called the ____
The right atrium is the first chamber that …
Right atrium
Deoxygenated blood flows into the right atrium from the body.
The vein that pumps deoxygenated blood into the right atrium is called the vena cava.
The right atrium is the first chamber that deoxygenated blood flows through.
Right ventricle
When the walls of the right atrium contracts, …
The atrioventricular valves prevent …
Then the walls of the right ventricle contracts, …
The semi-lunar valves prevent …
Right ventricle
When the walls of the right atrium contracts, deoxygenated blood flows into the right ventricle.
The atrioventricular valves prevent blood from flowing back into the atria from the ventricles.
Then the walls of the right ventricle contracts, blood is pumped out of the pulmonary artery to the lungs.
The semi-lunar valves prevent blood from flowing back into the right ventricle from the pulmonary artery.
Left atrium
Oxygenated blood flows into the left atrium from …
The vein that pumps oxygenated blood into the left atrium is called the ____
Left atrium
Oxygenated blood flows into the left atrium from the lungs.
The vein that pumps oxygenated blood into the left atrium is called the pulmonary vein.
Left ventricle
When the walls of the left atrium contracts, …
The atrioventricular valves prevent …
The walls of the left ventricle are considerably …
The left ventricle has to transport blood … the right ventricle only has to transport blood to …
Left ventricle
When the walls of the left atrium contracts, oxygenated blood flows into the left ventricle.
The atrioventricular valves prevent blood from flowing back into the atria from the ventricles.
The walls of the left ventricle are considerably thicker than the right ventricle.
The left ventricle has to transport blood all the way around the body but the right ventricle only has to transport blood to the lungs.
Aorta
When the left ventricle contracts, …
Oxygenated blood leaves the heart through …
The semi-lunar valves prevent blood from …
Aorta
When the left ventricle contracts, blood is pumped out of the heart to the rest of the body.
Oxygenated blood leaves the heart through the aorta.
The semi-lunar valves prevent blood from flowing back into the left ventricle from the aorta.
stages in the cardiac cycle
stages in the cardiac cycle
contraction of the atria
blood is forced into the ventricles
contraction of the ventricles
the AV valves shut
blood is forced out of the heart
the semi lunar valves shut
the atria and ventricles relax
Pressure in the atria
When the atria contract, …
When the atria relax and the ventricles contract, ….
When both the atria and the ventricles relax, …
Pressure in the atria
When the atria contract, the pressure in the atria increases.
When the atria relax and the ventricles contract, the pressure in the atria decreases.
When both the atria and the ventricles relax, there is a slight increase as the atria fill with blood again.
Pressure in the ventricles
When the atria contract, the pressure in the …
When the ventricles contract, the pressure increases dramatically. The pressure increases considerably more than when the ___ contract
When both the atria and the ventricles relax, there is a slight increase as the ventricles …
Pressure in the ventricles
When the atria contract, the pressure in the ventricles is relatively low. There is a slight increase in pressure as the ventricles fill with blood.
When the ventricles contract, the pressure increases dramatically. The pressure increases considerably more than when the atria contract.
When both the atria and the ventricles relax, there is a slight increase as the ventricles fill with blood again.
Volume in the atria
When the atria contract, …
When the atria relax and the ventricles contract, …
When both the atria and the ventricles relax, there is a slight decrease …
Volume in the atria
When the atria contract, the volume in the atria decreases.
When the atria relax and the ventricles contract, the volume in the atria increases again.
When both the atria and the ventricles relax, there is a slight decrease when blood flows into the ventricles from the atria.
Volume in the ventricles
When the atria contract, ..
When the ventricles contract, the volume ..
The volume decreases considerably more than when the ___contract.
When both the atria and the ventricles relax, …
Volume in the ventricles
When the atria contract, the volume in the ventricles increases slightly as they fill with blood.
When the ventricles contract, the volume decreases dramatically. The volume decreases considerably more than when the atria contract.
When both the atria and the ventricles relax, the volume increases as the ventricles expand again.
Veins
point of veins?
The lumen of veins is ___ than the arteries which allows …
There is a thin ___ and ___ in the vein walls.
___ are located throughout the veins to ensure blood flows towards the ___
Veins
Veins transport blood back to the heart.
The lumen of veins is wider than the arteries which allows the blood to flow at low pressure.
There is a thin muscle wall and elastic tissue in the vein walls.
Valves are located throughout the veins to ensure blood flows towards the heart.
Arterioles
When arteries reach an organ, …
The direction of blood flow can be controlled by contracting the arterioles to ..
Arterioles
When arteries reach an organ, they split into many smaller vessels called arterioles.
The direction of blood flow can be controlled by contracting the arterioles to restrict blood flow and relaxing the arterioles to allow blood to flow.
Arteries
Arteries transport …
Artery walls have …
The walls maintain a …
Elastic fibres in the artery wall allow the arteries to ….
The ____ is folded which also allows the arteries to stretch
Arteries
Arteries transport blood away from the heart to the organs.
Artery walls have thick layers of muscle.
The walls maintain a high pressure so blood can be pumped around the body.
Elastic fibres in the artery wall allow the arteries to stretch.
The endothelium is folded which also allows the arteries to stretch.
Features of veins:
Features of veins:
1 Wide lumen 2 Thin muscle wall 3 Elastic tissue in the walls 4 Valves to control blood flow
Artery walls have elastic fibres in the wall,
what does this allow them to do
Artery walls have elastic fibres in the wall, allowing them to stretch and spring back (recoil).
Walls
Capillary walls (endothelium) are \_\_\_? thick. This means that ... .... allows for efficient exchange.
Walls
Capillary walls (endothelium) are only one cell thick. This means that the diffusion distance of substances (e.g. oxygen) from the bloodstream to the tissues is very short. A short diffusion distance allows for efficient exchange.
Location
Capillaries …
There is a … between the capillaries and the body cells.
Exchange between the capillaries …
Location
Capillaries pass very close to the body cells.
There is a very short diffusion distance between the capillaries and the body cells.
Exchange between the capillaries and the body cells is rapid.
Surface area
Arterioles split into millions of capillaries that …
The networks create …
Networks of capillaries are called …
Surface area
Arterioles split into millions of capillaries that can form networks around the body cells (e.g. the network around the alveoli).
The networks create a large surface area for exchange of substances between the bloodstream and the tissues.
Networks of capillaries are called capillary beds.
blood Vessels characteristics
Veins
capillaries
Arterioles
Arteries
blood Vessels
Veins
Valves
Wide lumen
Capillaries
Thin endothelium
Capillary beds
Arterioles
Control blood flow
Arteries
High pressure
Thick layers of muscle
Pressure filtration
Pressure filtration
In order for the substances carried in the bloodstream (e.g. oxygen) to diffuse into the cells, they must first move out from the capillaries.
Substances move into tissue fluid from the capillaries in a process called pressure filtration.
Steps Involved in Formation of Tissue Fluid
Steps Involved in Formation of Tissue Fluid
fluid is forced out of the capillaries by pressure filtration
Deposition
The endothelium of arteries can become damaged by …
If …. and … continue to be deposited in the artery walls, the materials will begin to form …
Deposition
The endothelium of arteries can become damaged by the deposition of white blood cells and lipids.
If white blood cells and fatty materials continue to be deposited in the artery walls, the materials will begin to form hard, fibrous plaque.
As the fibrous plaque builds up, …
The flow of blood …
The narrower lumen also …
The presence of the fibrous plaque is called …
As the fibrous plaque builds up, the lumen of the artery becomes narrower.
The flow of blood through the arteries is restricted.
The narrower lumen also increases blood pressure.
The presence of the fibrous plaque is called an atheroma.
Atheromas can cause …
… is a type of disease that is associated with many atheromas.
Coronary heart disease
Atheromas can cause diseases of the heart.
Coronary heart disease (CHD) is a type of disease that is associated with many atheromas.
As fibrous plaque builds up, the artery lumen narrows. This ___ the flow of blood.
As fibrous plaque builds up, the artery lumen narrows. This restricts the flow of blood.
What causes the lumen of arteries to narrow in the formation of an atheroma?
What causes the lumen of arteries to narrow in the formation of an atheroma?
fibrous plaque
Atheromas can increase the risk of two types of diseases:
Atheromas can increase the risk of two types of diseases:
Aneurysm & Thrombosis
Aneurysm
Atheromas damage the … and increase …
The increased … can cause …
This …
Aneurysm
Atheromas damage the artery walls and increase blood pressure.
The increased blood pressure can cause the elastic fibres in the artery wall to swell in balloon-like structure.
This swelling is an aneurysm.
Thrombosis
Atheromas can damage the …, causing …
___ are transported in the bloodstream to …
A ____ can block blood flow in the artery.
Thrombosis
Atheromas can damage the artery walls, causing them to burst open.
Platelets are transported in the bloodstream to the damaged part of the artery wall.
The platelets accumulate and form a clot called a thrombus.
A thrombus can block blood flow in the artery.
Artery walls can burst open due to …
Platelets then accumulate and form a clot called a thrombus.
Artery walls can burst open due to damage caused by atheromas. Platelets then accumulate and form a clot called a thrombus.
High blood pressure
High blood pressure can be ____ or it can be caused by …
High blood pressure can contribute to the formation of …
High blood pressure
High blood pressure can be inherited or it can be caused by being overweight and consuming excessive alcohol.
High blood pressure can contribute to the formation of atheromas.
Diet
A diet that is high in … and ____ can lead to …
___ in the blood can contribute to the …
Diet
A diet that is high in saturated fat and salt can lead to high blood cholesterol levels.
Cholesterol in the blood can contribute to the formation of atheromas in the arteries.
Smoking cigarettes increases the risk of …
… found in cigarettes reduces the amount of ___ that can be …
Reduced transport of …
Smoking cigarettes increases the risk of high blood pressure.
Carbon monoxide found in cigarettes reduces the amount of oxygen that can be carried by haemoglobin in the blood.
Reduced transport of oxygen can increase the risk of a heart attack.
There are certain risk factors that can increase the chance of developing cardiovascular disease. These include:
There are certain risk factors that can increase the chance of developing cardiovascular disease. These include:
smoking
diet
high blood pressure
the walls of the … are a lot thicker than the … as it has to pump blood around the whole body
the walls of the left ventricle are a lot thicker as it has to pump blood around the whole body
Heart dissections allow the key features in the heart to be easily identified. Animal hearts can be sourced from the butcher. A larger heart allows …
Heart dissections allow the key features in the heart to be easily identified. Animal hearts can be sourced from the butcher. A larger heart allows …
Which blood vessel should be sliced to open the heart?
Which blood vessel should be sliced to open the heart?
aorta
What apparatus is used for dissecting an animal heart?
What apparatus is used for dissecting an animal heart?
1 Sharp blades 2 Gloves worn throughout 3 Disinfectant or other antimicrobial liquid
Guidelines
Guidelines
Gloves should be worn throughout dissection.
Hands must be washed using disinfectant after dissection.
Cuts should be made very carefully to avoid injury and allow you to see all the features.
Opening the heart
The heart can be opened by ….
Opening the heart allows you to …
The ___ can also be identified.
Opening the heart
The heart can be opened by slicing carefully from the aorta around the outside edge.
Opening the heart allows you to view the ventricular walls and other internal structures.
The valves can also be identified.
Ventricular walls
Comparing the right and left ventricles shows that …
This is a key feature of the heart.
Ventricular walls
Comparing the right and left ventricles shows that the left ventricular wall is much thicker than the right ventricle.
This is a key feature of the heart.
The xylem are plant vessels that are responsible for …
The structure of the xylem is specialised for this role.
The xylem are plant vessels that are responsible for transporting water and mineral ions. The structure of the xylem is specialised for this role.
Vessel elements
describe the xylem
The cells of the xylem are called …
The vessel elements in the xylem are ___.
Vessel elements
The xylem vessels are long, tubes of cells that run up the stem of plants.
The cells of the xylem are called vessel elements.
The vessel elements in the xylem are dead.
End walls
The vessel elements are …
There are ___ at the ends of each vessel element.
This creates a …
End walls
The vessel elements are stacked on top one another.
There are no cell walls at the ends of each vessel element.
This creates a continuous tube for water to flow through.
Lignin
The walls of the xylem are lined w …
Lignin reinforces the ___ of the vessel elements to provide …
Lignin
The walls of the xylem are lined with a waterproof polymer called lignin.
Lignin reinforces the walls of the vessel elements to provide structural support.
Cohesion-Tension Theory
… travel up the xylem through ___ and ___. The steps involved in this process are:
Cohesion-Tension Theory
… travel up the xylem through ___ and ___. The steps involved in this process are:
1) Transpiration
2) Tension
3) Cohesion
4) Diffusion in the roots
1) Transpiration
1) Transpiration
Some of the water in the leaves is used in photosynthesis.
Most of the water in the leaves evaporates in a process called transpiration.
2) Tension
2) Tension
The loss of water from the leaves creates tension in the xylem.
Tension is the formation of hydrogen bonds between water molecules and the sides of the xylem vessel elements.
Water in the xylem is pulled upwards by this tension towards the leaves.
3) Cohesion
3) Cohesion
Individual water molecules also form hydrogen bonds with each other. This process is called cohesion.
When water molecules are pulled up the xylem, other molecules of water are also pulled upwards due to cohesion.
The combination of cohesion and tension together continuously pull water upwards to replace water that has been lost in the leaves by transpiration.
4) Diffusion in the roots
4) Diffusion in the roots
When water is pulled up the stem, the water potential at the bottom of the plant decreases.
Water diffuses into the roots via osmosis down its water potential gradient.
Investigating Mass Transport in Plants
Mass transport can be investigated in two ways.
Investigating Mass Transport in Plants
Mass transport can be investigated in two ways.
Ringing
tracing
Q1.(a) (i) Give two ways in which the structure of starch is similar to cellulose.
Q1.(a) (i) Give two ways in which the structure of starch is similar to cellulose.
polymers
contain glycosidic bonds
(ii) Give two ways in which the structure of starch is different from cellulose.
(ii) Give two ways in which the structure of starch is different from cellulose.
starch contains a glucose and has no h bonds between molecules
In plants, mass transport of sugars takes place through columns of sieve cells in the
phloem. Other cells, called companion cells, transport sugars into, and out of, the
sieve cells.
The diagram shows the structure of phloem.
Structures I and J allow the transport of sugars between cells.
(i) Using the diagram, suggest and explain one other way in which sieve cells are
adapted for mass transport.
In plants, mass transport of sugars takes place through columns of sieve cells in the
phloem. Other cells, called companion cells, transport sugars into, and out of, the
sieve cells.
The diagram shows the structure of phloem.
Structures I and J allow the transport of sugars between cells.
(i) Using the diagram, suggest and explain one other way in which sieve cells are
adapted for mass transport.
- few organelles
- (So) easier flow
Using the diagram, suggest and explain one other way in which companion
cells are adapted for the transport of sugars between cells.
Using the diagram, suggest and explain one other way in which companion
cells are adapted for the transport of sugars between cells.
Mitochondria release energy (atp)
Q2.Organic compounds synthesised in the leaves of a plant can be transported to the plant’s
roots.
This transport is called translocation and occurs in the phloem tissue of the plant.
(a) One theory of translocation states that organic substances are pushed from a high
pressure in the leaves to a lower pressure in the roots.
Describe how a high pressure is produced in the leaves.
Q2.Organic compounds synthesised in the leaves of a plant can be transported to the plant’s
roots.
This transport is called translocation and occurs in the phloem tissue of the plant.
(a) One theory of translocation states that organic substances are pushed from a high
pressure in the leaves to a lower pressure in the roots.
Describe how a high pressure is produced in the leaves.
- Water potential becomes lower / becomes more negative (as sugar enters
phloem) ; - Water enters phloem by osmosis;
- Increased volume (of water) causes increased pressure.
https://pmt.physicsandmathstutor.com/download/Biology/A-level/Topic-Qs/AQA/3-Exchange-of-Substances/Set-B/Mass%20
PCMBS is a substance that inhibits the uptake of sucrose by plant cells.
Scientists investigated the effect of PCMBS on the rate of translocation in sugar
beet.
The figure below shows their results.
Time / minutes
(b) During their experiment, the scientists ensured that the rate of photosynthesis of
their plants remained constant.
Explain why this was important.
(c) The scientists concluded that some translocation must occur in the spaces in the
cell walls.
Explain how the information in the figure above supports this conclusion.
https://pmt.physicsandmathstutor.com/download/Biology/A-level/Topic-Qs/AQA/3-Exchange-of-Substances/Set-B/Mass%20
PCMBS is a substance that inhibits the uptake of sucrose by plant cells.
Scientists investigated the effect of PCMBS on the rate of translocation in sugar
beet.
The figure below shows their results.
Time / minutes
(b) During their experiment, the scientists ensured that the rate of photosynthesis of
their plants remained constant.
Explain why this was important.
(b) 1. Rate of photosynthesis related to rate of sucrose production;
2. Rate of translocation higher when sucrose concentration is higher.
(c) The scientists concluded that some translocation must occur in the spaces in the
cell walls.
Explain how the information in the figure above supports this conclusion.
