Lecture: Phloem Flashcards
what is the function of phloem?
conduction of products of Ps
what products of Ps does phloem conduct?
sugar, some amino acids
what are the structural elements of phloem?
- parenchyma
- sclerenchyma
- conducting sieve elements
what are the two types of conducting sieve elements?
- albuminous cells
2. companion cells
sieve cells are
less efficient, primitive
what plant groups have sieve cells?
ferns and gymnosperms (not angiosperms)
what cells are associated with sieve cells?
albuminous cells
what is the structure of sieve cells?
sieve areas (side walls) with pit membrane on all walls, pit fields with plasmodesmata
sieve-tube cells are
more advanced and efficient
what plant groups have sieve-tube cells?
angiosperms
what cells are associated with sieve-tube cells?
companion cells
what is the structure of sieve-tube cells?
sieve areas (side walls) and sieve plates (end walls with large pores)
which conducting sieve element is more efficient at transporting water with sugar and preventing air bubbles?
sieve-tube cells
how many cell walls in sieve elements?
only primary
sieve elements are ____ at maturity
alive, but braindead
what structures do sieve elements lose at maturity?
nuclei, ribosomes, dicytosomes, tonoplast
what structures do sieve elements keep at maturity?
plasmalemma, ER, mitochondria, some plastids, cytoplasm
what controls the sieve cells?
albuminous cells
what controls the sieve-tube cells?
companion cells
what is the relationship between the albuminous cell and sieve cell?
neighbours
what is the relationship between the companion cell and the sieve-tube cell?
sister
unlike tracheary elements, the lifespan of sieve elements is __
short (<1 year - 5-10 years)
what are the functions of albuminous/companion cells?
- brains of their associated cells
2. control loading / unloading
what direction does phloem move in plants?
bidirectional
by what two methods is long-distance transport of phloem carried out?
- active transport (ATP)
2. passive transport (osmosis)
the location of source / sink for phloem will change based on
- season
2. lifestage
what is the source / sink of phloem in summer?
source: site of Ps
sink: site of use/storage
what is the source / sink of phloem in winter?
source: roots/storage site
sink: site of use
how does lifestage of a plant influence the movement of phloem?
as plant recahes reproductive stage, it requires more phloem to be redirected to the production of reproductive structure
how fast does phloem move through phloem?
50-100cm an hour
how do we know the speed at which phloem travels?
aphids penetrate sieve tube cell and phloem gushes into insect, and will continue to gush if insect removed
what is the pressure flow theory (mass flow hypothesis) for the movement of phloem?
long distance transport based on
- concentration gradient (osmotic) and turgor pressure gradient
- water exchange with xylem
loading and unloading phloem is a(n) (active/passive) process?
active, requires ATP
long distance transport by mass flow is a(n) (active/passive) process?
passive, no ATP
what causes the bulk of the transport of phloem?
turgor pressure gradient
what are the “main players” of phloem transport?
- sugar source
- suagr sink
- sieve elements
- associated cells
- tracheary elements
what are the two routes for loading phloem?
- symplastic pressure flow
2. apoplastic loading
where does phloem travel through in symplastic loading?
plasmodesmata
where does phloem travel through in apoplastic loading?
cell wall
in what order do symplastic and apoplastic loading occur? Which requires ATP?
- symplastic
2. apoplastic (ATP)
how is sugar loaded into a sieve tube celll?
actively and controlled by the associated cell
what happens once sugar has been loaded into sieve tube cell?
osmotic gradient is created and water from tracheary element moves to sieve tube cell, increasing turgor pressure
what happens once water from tracheary element has increased the tugor pressure of the sieve tube cell?
sugar is pushed to adjacent tube (from source to sink)
unloading sugar at the sink is a(n) (active/passive) process?
active (ATP)
what controls unloading of sugar?
associated cells
once sugar has been unloaded, what happens to the osmotic gradient? Turgor Pressure?
reverses and water moves back to tracheary element, decreasing turgor pressure
loading and unloading phloem creates what two types of gradients?
- concentration
2. pressure
