Topic 9.2: Transport in the Phloem of Plants Flashcards
Phloem function
Transport sap
Phloem composition
a) Sieve element cells (Formation of sieve tube)
b) Companion cells
(Loading / Unloading of sap)
Traits of sieve element cells
a) Connected by porous sieve plates
b) No nuclei
c) Rigid cell walls
Traits of companion cells
a) Infolding membrane
b) Multiple mitochondria
c) Transport proteins
Main difference between xylem and phloem
Xylem (Inside) have larger cavities than phloem (Outside)
Vascular tissue in roots of monocotyledons
a) Radiating circle of vessels
b) Xylems are located more centrally
Vascular tissue in roots of dicotyledons
a) Xylem in cross-like shape
b) Phloem surrounding it
Vascular tissue in stem of monocotyledons
a) Scattered arrangement
b) Phloem is outside
Vascular tissue in stem of dicotyledons
a) Circular arrangement
b) Phloem and xylem separated by cambium
Differences between xylem and phloem
a) Transport
b) Position
c) Cell fusion
d) Type of tissue
a) H2O / Minerals | Sap
b) Inside | Outside
c) Continuous | Porous cell sieve plates
d) Dead | Living
Definition of translocation
Movement of organic compounds from sources to sinks
a) Source = Site of synthesis
b) Sink = Site of use / storage
Active translocation
a) Phloem loading
b) Mass flow at the source
c) Mass flow at the sink
Phloem loading
Organic compounds produced at the source are actively loaded into phloem sieve tubes by companion cells via cotransport of sucrose and H+
Mass flow at the source (2)
a) Active transport of solutes into the phloem makes the sap solution hypertonic, causing water to be drawn from the xylem via osmosis
b) Due to the incompressibility of water, this buildup of water causes the hydrostatic pressure to increase, forcing sap to move towards areas of lower pressure
Mass flow at the sink (2)
a) The solutes within the phloem are unloaded by companion cells and transported into sinks, causing the sap to become hypotonic
b) Water is drawn out of the phloem and back to xylem by osmosis
