Mass transport (7) Flashcards
What is the structure of haemoglobin?
- globular
- water soluble
- 4 polypeptide chains each carrying a haem group (quaternary structure)
What is the role of haemoglobin?
O2 molecules bind to haem groups and are carried around body to where they are needed in respiring tissues
Where is haemoglobin found?
in red blood cells
What do oxyhaemoglobin dissociation curves show?
saturation percentage of haemoglobin with O2
plotted against partial pressure of O2 (kPa)
curve to left shows haemoglobin has high affinity for O2
What are 3 reasons for the mammalian circulatory system?
1) suitable medium for transport as it is water-based to allow substances to dissolve
2) means of maintaining pressure throughout body
3) means of controlling flow so it remains unidirectional such as valves
What is translocation?
where organic materials are transported around the plant
Why does O2 bind to haemoglobin in the lungs?
1) partial pressure of O2 is high
2) low concentration of CO2 in lungs so affinity is high
3) positive cooperativity
What is positive cooperativity?
after 1st O2 binds, binding of subsequent molecules is easier, but slightly harder for the 4th as there is low chance of finding a binding site
What are 3 factors affecting O2 and haemoglobin binding?
1) partial pressure/concentration of O2
2) partial pressure/concentration of CO2
3) saturation of haemoglobin with O2
How does high partial pressure of O2 affect O2 and haemoglobin binding?
if partial pressure of O2 is high, affinity of haemoglobin for O2 will also be high, so O2 binds tightly to haemoglobin
How does low partial pressure of O2 affect O2 and haemoglobin binding?
if partial pressure of O2 is low, O2 is released
How does high partial pressure of CO2 affect O2 and haemoglobin binding?
if partial pressure of CO2 is high, conditions become acidic causing haemoglobin to change shape, so affinity of haemoglobin for O2 decreases, releasing O2 (this is known as the Bohr effect)
What is the Bohr effect?
when partial pressure of CO2 is high, conditions become acidic causing haemoglobin to change shape, so affinity of haemoglobin for O2 decreases, releasing O2
How does the saturation of haemoglobin with O2 affect O2 and haemoglobin binding?
- hard for 1st O2 molecule to bind
- once it does it changes shape to make it easier for 2nd + 3rd molecules to bind (this is known as positive cooperativity)
- it becomes slightly harder for 4th as low chance of finding a binding site
Label diagram of heart.
Use notes.
What are the 2 chambers of the heart?
atria and ventricles
What is the structure of the atria and how does this relate to its function?
thin-walled + elastic
so they can stretch when filled with blood
What is the structure of the ventricles and how does this relate to its function?
thick muscular walls pump blood under high pressure
Which side of the heart is thicker and why?
left
has to pump blood all the way round the body
What are the 2 vessels in the heart?
arteries and veins
What is the structure of the arteries and how does this relate to its function?
- thick walls to handle high pressure without tearing
- muscular and elastic tissue to control blood flow
What is the structure of the veins and how does this relate to its function?
thin walls due to low pressure, therefore need valves
less muscular and elastic tissue as they don’t control blood flow
Why are both the pumps (left and right) needed?
- to maintain blood pressure around whole body
- when blood passes through narrow capillaries, pressure drops sharply, without 2 pumps it would not flow strongly enough to continue around the whole body
- returned to heart to increase pressure
What are the 2 steps that happen during atrial systole?
1) atria contract
2) remaining blood pushed into ventricles
What are the 7 steps that happen during cardiac diastole?
1) heart is relaxed
2) blood enters atria
3) pressure increases
4) atrioventricular valves pushed open
5) allows blood to flow into ventricles
6) heart pressure lower than in arteries
7) semilunar valves remain closed
What are the 3 stages of blood movement through the heart?
cardiac diastole
atrial systole
ventricular systole
What are the 5 steps that happen during ventricular systole?
1) ventricles contract
2) pressure increases
3) atrioventricular valves close
4) semilunar open
5) blood flows into arteries
What is meant by myogenic?
heart’s contraction is initiated from within muscle itself, rather than by nerve impulses
How does the structure of capillaries relate to its function?
- walls only 1 cell thick so short diffusion path
- very narrow so can permeate tissues and red blood cells can lie flat against wall, effectively delivering O2 to tissue
- numerous and highly branches so have large SA
What is tissue fluid?
watery substance containing glucose, amino acids, O2 and other nutrients
What is the function of tissue fluid?
supplies glucose, amino acids, O2 and other nutrients to cells and removes waste materials
How is tissue fluid formed?
- blood pumped through increasingly small vessels creating hydrostatic pressure, which forces fluid out of capillaries
- bathes cells, then returns to capillaries when hydrostatic pressure is low enough
How is water transported in plants?
through xylem vessels
What are xylem vessels?
long, continuous columns that also provide structural support to the stem
What are the 3 components of phloem vessels?
sieve tube elements
companion cells
plasmodesmata
What is the role of sieve tube elements?
form a tube to transport sucrose in the dissolved form of sap
What is the role of companion cells?
involved in ATP production for active loading of sucrose into sieve tubes
What is the plasmodesmata and its role?
gaps between cell walls where cytoplasm links, allowing substances to flow
What are 3 pieces of evidence for the mass flow hypothesis?
- sap released when stem cut so must be pressure in phloem
- higher sucrose concentration in leaves than roots
- high sucrose levels in leaves means high levels of sucrose in the phloem
What are 3 pieces of evidence against the mass flow hypothesis?
- structure of sieve tube elements hinders mass flow
- not all solutes move at same speed, but would in mass flow
- sucrose delivered at same rate, not to areas of low concentration first
What are the 2 experiments that provide evidence for the mass flow theory?
tracing experiment
ringing experiment
What is the tracing experiment?
- plants grown in presence of radioactive CO2
- incorporated into plant’s sugars
- autoradiography shows areas exposed to radiation, which is where the phloem is
What is the ringing experiment?
1) bark and phloem removed in a ring, leaving behind the xylem
2) tissues above swell due to accumulation of sucrose as tissue below begins to die
3) therefore sucrose must be transported in the phloem
What is the cohesion-tension theory?
- water molecules form H bonds with each other, causing them to ‘stick’ together (cohesion)
- surface tension of water also creates this sticking effect
- therefore, as water is lost through transpiration, more can be drawn up the stem
How does sucrose move into the phloem?
(2 points)
1) enters companion cells by active loading, which uses ATP + diffusion gradient of H+
2) sucrose diffuses into sieve tube elements through plasmodesmata
How does the phloem transport sucrose in the plant?
1) as sucrose moves into the sieve tube elements, water potential in phloem reduces
2) water enters via osmosis from xylem and increases hydrostatic pressure
3) water moves along sieve tube elements towards area of lower hydrostatic pressure
4) sucrose diffuses into surrounding cells where is it needed
