Translocation and phloem tissue Flashcards
Translocation is…
the transport of soluble organic substances within a plant.
Assimilates are…
substances which the plant has made itself.
Assimilates are transported in…
sieve elements found in phloem tissue.
Sieve tubes make up…
the phloem. They are tube-like structures, made of living cells.
A sieve tube is made of many…
elongated sieve elements, joined end to end vertically to form a continuous tube.
Sieve element is…
a living cell. The amount of cytoplasm compared to other plant cell is very low and there is no nucleus and no ribosomes.
Sieve plate is formed where…
the end walls of two sieve elements meet. They are made of the walls of both elements, perforated by large pores.
Companion cells have a large number of…
mitochondria and ribosomes as they are metabolically very active.
The companion cells are closely associated…
with the neighbouring sieve element.
Numerous plasmodesmata pass through the cell walls of…
companion cell and the sieve element, making direct contact between the cytoplasm of one and another.
Phloem sap is…
the liquid inside phloem sieve tubes.
The contents of sieve tubes are under…
high pressure.
When a sieve tube is cut…
the release of pressure inside the tube causes a surge of its contents towards the cut.
When the contents of the sieve tube come up…
against a sieve plate, they block it.
Callose is…
a carbohydrate used to seal the sieve plate and prevent the escape of contents.
Phloem sap is also moved by…
mass flow.
To create pressure differences in phloem…
energy is needed, so phloem transport is active transport.
The pressure difference is created by…
active loading of sucrose into sieve elements, at the place from which sucrose is to be transported.
A source is a part of…
plant where sucrose is loaded into the phloem.
A sink is a part of…
plant where sucrose is unloaded from the phloem.
High concentration of sucrose in sieve element, lowers…
the water potential, so water enters the sieve element by osmosis. This increases a hydrostatic pressure and pressure gradient is created between sink and source.
Photosynthesis produces…
triose sugars which are converted to sucrose.
The sucrose moves from mesophyll cell to…
phloem tissue by a simplistic or apoplastic pathway.
Sucrose is loaded to…
the companion cell by active transport.
The loading is done by…
pumping H+ ions out of the companion cell into its cell walls, using ATP.
Increased concentration of H+ ions in…
the apoplastic pathway outside the companion cell.
The H+ ions can move back down…
the concentration gradient, through protein which acts as a carrier for both H+ and sucrose at the same time.
The sucrose molecules are carried through this…
co-transporter molecule into the companion cell against the concentration gradient for sucrose.
The sucrose moves from companion cells to sieve tubes through…
plasmodesmata.
Unloading of sucrose also requires…
energy and uses both apoplastic and symplastic pathways.
To maintain the gradient in tissues for sucrose…
enzyme invertase breaks sucrose to fructose and glucose.
