plant adaptations and phloem translocation

Question 1

what are xerophytes

Answer 1

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

Question 2

what adaptations do xerophytes have

Answer 2

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

Question 3

adaptations of marram grass

Answer 3

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

Question 4

what is a hydrophyte

Answer 4

live in water or on surface

Question 5

adaptations of hydrophytes

Answer 5

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

Question 6

what is the phloem

Answer 6

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

Question 7

what are companion cells

Answer 7

controls metabolism of tube elements

Question 8

what does phloem tisses transport

Answer 8

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

Question 9

what substances does the phloem transport

Answer 9

sucrose
amino acids
hormones
minerals

Question 10

what is mass flow theory

Answer 10

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

Question 11

name the four phloem experiments

Answer 11

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

Question 12

outline the ringing experiment

Answer 12

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

Question 13

outline the radioactive tracers and autoradiography

Answer 13

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

Question 14

outline the aphid experiments

Answer 14

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

Question 15

outline the aphid and radioactive tracers experiments

Answer 15

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