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Flashcards in plant adaptations and phloem translocation Deck (15)
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what are xerophytes

plants that grow in conditions with very little liquid water
e.g. desert and ice or snow covered areas
they have adaptations to help conserve water and prevent water loss


what adaptations do xerophytes have

spikes not leaves
thick stem for water storage
spikes trap water vapour which causes equilibrium as slows down the diffusion of water out through the stomata


adaptations of marram grass

leaf rolled up to trap air inside
thick waxy cuticle to reduce water evaporation from the surface
trapped air in centre with a high water potential
hairs on lower surface reduce movement of air
stomata in pits to trap air
reduced number of stomata
deep root system
fleshy or succulent stem to store water


what is a hydrophyte

live in water or on surface


adaptations of hydrophytes

leaves often contain air spaces to help them float
less lignifications of xylem as water supports plants
increase surface area
thin cuticle
many stomata
fewer roots


what is the phloem

living tissues
sieve tube elements (with no nucleus or organelles)
sieve tube/plate is perforated


what are companion cells

controls metabolism of tube elements


what does phloem tisses transport

substances made in the leaves to all other parts of the plant. this transport is called translocation


what substances does the phloem transport

amino acids


what is mass flow theory

fluids can move freely in sieve tubes following the hydrostatic pressure gradient
sucrose is actively loaded into the sieve tube from the source cells
water follows the sucrose so the pressure in the sieve tube increases
a sink cells unloads the sucrose so the pressure in the sieve tube decreases


name the four phloem experiments

ringing experiments
radioactive tracers and autoradiography
aphid experiments
aphid and radioactive tracers


outline the ringing experiment

cylinders of outer bark tissues are removed along with the phloem. a lot of sucrose gathers above the cut and no sucrose is present below the cut showing that the sucrose was used but not replaced as it was prevented from moving downwards


outline the radioactive tracers and autoradiography

a plant photosynthesises in the presence of a radioactive isotope 14CO2. a stem section is placed on a film which is exposed if there is radiation producing an autoradiograph. shows that phloem translocates sucrose


outline the aphid experiments

hollow needlelike mouths called a stylet insert into a phloem and its contents. exude under high pressure. in some the aphid was anaesethised and removed. stylet remained and was collected and showed presence of sucrose


outline the aphid and radioactive tracers experiments

extended to plants which had been photosynthesising 14co2. showed the radioactivity and sucrose moved at 0.5-1 mn-1 which is much faster than diffusion so some additional mechanism has to be considered