mass transport Flashcards
what is transported in the xylem and phloem?
xylem: water and mineral ions
phloem: organic substances eg sucrose/sugars
adaptations of xylem
end walls broken = continuous column
strengthened with lignin = support
no cytoplasm/organelles = doesn’t obstruct continuous flow
cohesion tension theory
water evaporates from mesophyll cels in leaf
water vapour diffuses out of leaf through stomata
down concentration gradient between leaf and air
creates tension which pulls more water into the leaf
water moves out of xylem into leaf cells
creates tension on column of water in xylem
water molecules cohesive, joined by hydrogen bonds
moves upwards
water enters root hair cells by osmosis
as water pulled upwards
evidence for cohesion tension
change in trunk diameter
- increased transpiration = narrower trunk as xylem pulled in by cohesion
translocation (mass flow)
at source
Sucrose actively transported into phloem
By companion cells
decreases water potential in phloem
so water moves in by osmosis from xylem
creates high hydrostatic pressure
at source
sugars used in respiration or stored
lower water potenial
so water moves out by osmosis into xylem
low hydrostatic pressure
creates pressure gradient
= mass transport from source to sink
evidence for mass flow
higher concentration of sucrose in sap nearer source than sink
- suggests osmosis would occur to move sugars
radioactive tracers to track movement of sugars
puncture phloem
sap flows out fast (faster nearer leaves then stem)
suggests there’s a pressure (gradient)
metabolic inhibitor (stops ATP production) stops translocation
suggests active transport involved
evidence against mass flow
sugar moves to many sinks
not just ones with lower water potential
sieve plates create a barrier
its of pressure needed to get solutes through fast enough
what is transpiration?
loss of water vapour from stomata by diffusion
due to water potential gradient between leaf and air
factors affecting transpiration
light - positive correlation
- stomata open when light for photosynthesis, allow transpiration
temperature - higher = faster
- warmer water molecules have more kinetic energy so evaporate faster, creates gradient so water diffuses out leaf faster
humidity - lower = faster
- air dry, concentration gradient between leaf and air increased, faster
wind - windier = faster
- blows water molecules from around stomata, increases concentration gradient
potometer
measures water uptake (assumes same as transpiration)
cut the shoot underwater
(stops air entering xylem)
cut at slant
(increase surface area)
assemble underwater so no air can enter
remove but keep end of capillary tube submerged in beaker
make sure water and air tight
shut tap (attached to resevoir, used to reset water bubble if needed)
remove end of capillary tube from beaker until air bubble formed before replacing it
record starting position and time
distance moved per unit time
rate of movement is estimate of rate of transpiration
how are radioactive tracers used to investigate translocation?
supply plant with organic substance that has a radioactive label
eg carbon dioxide (with radioactive isotope)
will be incorporated with organic substances in leaf and move around by translocation
movement tracked using autoradiography
- placed on photographic film
- turns black where radioactivity is
gas exchange in single celled organisms
absorb and release gas by diffusion through outer surface
large surface area to volume ratio
thin surface and short diffusion distance
gas exchange in fish
water enters fish through mouth
passes out through gills
each gill made of thin plates called gill filaments
- give large surface area for exchange
gill filaments covered in lamellae
- increase surface area more
lamellae have thin surface layer of cells and many blood capillaries to aid diffusion
by the counter current system
outline the counter current system
blood flows through lamellae in one direction and water flows in the opposite direction
maintains large concentration gradient between water and blood along whole lamellae
allows as much oxygen as possible to diffuse into blood
gas exchange in insects
air moves into tracheae through spiracles (pores)
oxygen travels down concentration gradient to cells
branch into tracheoles - have thin permeable walls straight to cells
carbon dioxide from cells move down its own concentration gradient to be released
gases not carried in blood
use rhythmic abdominal pumping to move air in and out of spiracles
gradient created as oxygen used by respiring cells