Mass Transport in Plants - Phloem Flashcards
3 parts of phloem tissue
- companion cell
- sieve tube element
- fibre and parenchyma
name given to the perforated end walls in sieve tubes
sieve plates
structure of sieve tube element
- elongated, stacked to form a continuous tube
- end walls start to diintegrate
- no nucleus or other organelles
function of the sieve tube
transport organic solutes (products of PS): sucrose and a.a. as sap
function of the perforated end walls in sieve tubes
allow cytoplasmic connections
how are companion cells connected to the sieve tube?
by plasmodesmata
functions of a companion cell
- synthesise ATP and proteins for sieve tube
- load and unload sucrose to and from sieve tube
when can the sink become the source?
when stored products are used
directionof transport in phloem
from source to sink
what is the source in translocation?
where sucrose and other organic solutes are made
what is the sink in translocation?
where sucrose is stored or used
is translocation unidirectional or bidirectional?
bidirectional
3 suggested theories of translocation
- diffusion through phloem
- cytoplasmic streaming
- munch’s mass flow hypothesis
criticisms of diffusioin through phloem and cytoplasmic streaming theories
- only effective across sort distances, too slow across long distances
- cytosol of cytoplasm moves in currents, carrying moleculs through cells
2 assumptions of munch’s mass flow hypothesis
- passive flow of sucrose
- sucrose flowing down hydrostatic pressure gradient