Chapter 7 - Mass transport Flashcards
what is the quarternary structure of haemoglobin?
four polypeptides, each associated with a haem group which contains Fe 2+ which can combine with one molecule of oxygen each
what is the term for taking up oxygen in haemoglobin?
loading and unloading
what is the role of haemoglobin? (2)
- readily associate with oxygen at gas exchange (high partial pressure)
- readily dissociate at low partial pressures such as respiring tissues
why are their different haemoglobin in different animals?
different partial pressure e.g. high altitude
different dissociating required e.g. lugworms
explain the shape of oxygen dissociation curves (4)
- difficult for first molecule to bind = shallow curve gradient
- first molecule binding changes the shape making it easier for subsequent molecules to bind
- positive cooperativity, the gradient steepens
- lower probability of oxygen binding when oxygen is highly loaded means gradient levels off
what are the effects of CO2 on haemoglobin? (3)
- reduced affinity for oxygen
- release oxygen more readily at high CO2 conc. ,e.g. respiring tissues
- slightly acidic, CO2 changes shape of haemoglobin
state the sequence of vessels in the heart from the vena cava to the aorta (12)
- vena cava
- right atrium
- atrioventricular valve
- right ventricle
- semi-lunar valve
- pulmonary artery
- (lungs)
- pulmonary vein
- left atrium
- atrioventricular valve
- left ventricle
- semi-lunar valve
- aorta
name the 3 stages of the cardiac cycle
diastole
atrial systole
ventricular systole
what are the valves in veins and what do they do?
pocket valves prevent backflow
what is the action of diastole? (3)
- blood returns to atria through vena cava and pulmonary vein
- when pressure exceeds that in the ventricles the semi-lunar valves open allowing blood to drain into ventricles by gravity
- semi-lunar valves remain open until the pressure in the atria has decreased below that of the ventricles
what is the action of atrial systole?
both atria contract at the same time along with further recoil of the ventricles, forcing the remaining blood in the atria into the ventricles
what is the action of ventricular systole? (2)
- ventricles contract together, AV valves shut
- pressure within ventricles rises further forcing the semilunar valves of aorta open due to higher pressure in ventricles
- (creates high pressure for blood to go round whole body and back)
state the cardiac output calculation
heart rate x stroke volume = cardiac output
name the types of blood vessels (4)
- arteries
- arterioles
- capillaries
- veins
what are capillaries made from?
lining layer/epethelial cells
name the structures of arteries arterioles and veins (5)
- tough fibrous outer layer
- muscle layer - contraction for blood pressure
- elastic layer - recoil
- endothelium - reduce friction
- lumen - cavity
compare the main function of arteries to that of capillaries (2)
- arteries carry blood around whole body by maintaining constant high blood pressure
- capillaries, allow diffusion due to short diffusion pathway
outline tissue fluid formation (2)
- hydrostatic pressure created by pumping of the heart and narrow capillaries
- at arteriole end of capillaries hydrostatic pressure forces tissue fluid into surrounding cells
what forces resist the formation of tissue fluids? (2)
- hydrostatic pressure of surrounding cells and fluid outside
- lower water potential of blood due to plasma proteins
outline the return of tissue fluid to the circulatory system (5)
- reduced hydrostatic pressure at venous end due to loos of fluid
- tissue fluid forced back into capillaries
- capillaries have lower water potential
- water moves down water potential gradient
- remainder absorbed into lympatic capillaries which drain into the blood
name the process of water loss through evaporation in plants
transpiration
how does water move up the stem into the leaves?
in a continuous column of water up the xylem (caused by cohesion) known as transpiration pull, cohesion tension theory
what is the function of the xylem?
to carry water up the stem from the roots (transport of water)
what is the evidence in support of cohesion tension theory? (2)
- change in diameter of tree trunks e.g. after rain
- if xylem is broken, column of water is broken and water no longer passes upwards, in addition the the fact air is drawn in showing tension
what is the function of the phloem?
transport of organic molecules
what theory governs the mechanism of translocation?
mass-flow hypothesis
outline the process by which sucrose enter sieve elements (3)
- sucrose is manufactured and diffuses down conc. gradient into companion cells
- hydrogen ions are actively transported from companion cells into spaces in the cell wall
- hydrogen ions diffuse back down concentration gradient into the phloem through specific co-transport proteins with sucrose
outline the process of mass flow through sieve elements (4)
- lower water potential in the sieve element, water moves in from xylem
- causes greater hydrostatic pressure
- inverse is true at sink with respiring cells
- mass flow of sucrose solution down hydrostatic pressure gradient to sink
by what process does the sucrose leave the sieve elements once at the sink?
active transport
what is the evidence to support mass flow? (5)
- sap released from sieve tubes when cut shows pressure
- conc. of sucrose higher in leaves
- downward flow only occurs in day when leaves are photosythesising
- sucrose increase in leaves results in sucrose increase in phloem
- companion cells contain many mitochondria for active transport
evidence questioning mass flow? (3)
- unclear function of sieve plates
- not all solutes move at same speed
- sucrose delivered at same rate to all regions
types of xylem/phloem experiments (2)
- ringing experiments
- tracer experiments
what is the evidence that translocation occurs in the phloem? (3)
- phloem cut, organic molecules come out
- plants given tracer CO2 show tracer in phloem after a short time
- removal of a ring of phloem on a plant leaves sugars building up above the ring
outline a ringing experiment on a tree and the expected results (2)
- remove ring of protective layer and phloem
- area immediately above ring swells with sugars
outline a tracer experiment and the expected results (4)
- radioactive carbon absorbed by plant and incorporated into sugars
- after some time thin slices of plant take and placed over X-ray photography film
- were film is blackened shows where radioactive isotope in sugars is
- these correspond with where the phloem is
