Transport in plants

Question 1

what does translocation do? where does it take place phloem or xylem?

Answer 1

transports assimilates from source to sink in phloem

Question 2

describe the process of translocation

Answer 2

1. sucrose produced when plant (leaves) photosynthesise
2. sucrose loaded into phloem via active transport
3. hydrogen ions flow down conc gradient causing inward flow of sucrose into companion cell increasing solute concentration
4. sucrose diffused through plasmodesmata into the sieve tube elements , lowering water potential
5. causes water to enter via osmosis from the xylem vessels , increasing hydrostatic pressure
6. phloem sap moves down sieve tube elements towards sinks (mass flow)
7. at the sink, sucrose unloaded and converted into glucose for respiration

Question 3

why do plants need transport systems?

Answer 3

small SA:V ratio , diffusion would be too slow

Question 4

xylem contains pits, what are pits roles?

Answer 4

allow water and dissolved substances to pass between vessels , allows water to move out of xylem

Question 5

role of lignin in xylem cell walls?

Answer 5

impermeable - prevents substances passing through cell wall
helps prevent vessels from collapsing
structure and support

Question 6

role of xylem fibres?

Answer 6

provide mechanical support for the plant

Question 7

role of parenchyma cells in xylem tissue?

Answer 7

store of starch and contain tannins

Question 8

is xylem living or non-living?

Answer 8

non-living

Question 9

is phloem living or non living?

Answer 9

living

Question 10

name two assimilates transported by phloem cells?

Answer 10

sucrose and amino acids

Question 11

role of phloem?

Answer 11

transport assimilates from the plant leaves to other part of plant

Question 12

whats the fluid moving in the phloem called?

Answer 12

sap

Question 13

do sieve tube elements have organelles?

Answer 13

no , most are lost to transport the sap

Question 14

role of sieve plates?

Answer 14

allow phloem sap to move between cells

Question 15

in phloem tissue what provides support?

Answer 15

fibres and sclereids

Question 16

name some adaptions of xerophytes?

Answer 16

reduced surface area : volume ration
tomato on the inside in sunken pits
only open stomata at night to reduce water loss
thick waxy cuticle to prevent evaporation

Question 17

how are companion cells and sieve tubes linked in a plant?

Answer 17

via microscopic channels like the plasmodesmata

Question 18

define mass flow?

Answer 18

bulk transport of sucrose from an area of high hydrostatic pressure at the source to low hydrostatic pressure in the sink