functions and structure of plants Flashcards
where is the xylem found
vascular bundles
what is the function of xylem
-Vascular tissue that carries dissolved minerals and water up the plant
-Structural support
-Food storage
what is the function of the phloem
Transport organic compounds up and down the cell
properties of phloem
has perforated cross walls
-made of living cells
-thin cell wall
-cell wall made of cellulose
properties of xylem
-made of dead cells
-cell wall made up of lignin
-thick cell walls
-tissue contains fibres
-no cytoplasm or organelles
what, where and function is the vascular bundle
-made up of xylem and phloem tissue
-distributed throughout the plant
-has structural support purposes
what does the vascular bundle in the roots do
-enables the plant to push down into the root
-xylem tissue is in the centre as it is the strongest ( X structure )
-phloem is around the xylem in four seperate sections
structure of the vascular bundle in the leaf
-xylem located on top of the phloem
what does the vascular bundle do in the stem
-provides additional support to the stem
-cambium later contains meristem cells
what does lignin do in the xylem
-lignin imprégnâtes the walls of the cell making it waterproof, this kills the cell
-the lignin strengthens the vessel walls and prevents the vessel from collapsing
-keeps the vessel open
-prevents vessel from being too rigid and allows some flexibility of the stem
what happens when lignification is incomplete
leaves gaps in the cell wall
what do the gaps in xylem wall form
bordered pits
what do bordered pits do
-allow water to leave one vessel and pass into the next vessel
-allow water to leave the xylem and pass into the living parts of the plant
what does phloem tissue consist of
sieve tubes made up of sieve tube elements and companion cells
properties of sieve tubes
-no nucleus
-small cytoplasm
-very thin walls
this leaves little space for flow of sap to occur
what is at the end of sieve tubes
perforated cross walls- sieve plates
the perforations allow movement of the sap from one element to the next
where are companion cells found
in between the sieve tubes
properties of companion cells
-large nucleus
-dense cytoplasm
-a lot of mitochondria for active processes
what do companion cells do
contain many mitochondria as the phloem requires active transport to move sap in translocation
properties of xylem
-made of dead cells
-cell wall made up of lignin
-thick cell walls
-tissue contains fibres
how do sugars move along the phloem at the source
-sugars are actively moved into the sieve tube cytoplasm, decreases the water potential
-therefore water moves into the sieve cells by osmosis
-this increases the hydrostatic pressure inside the phloem, water moves to decrease their pressure
how do sugars move along the phloem at the source
-sugars are actively moved into the sieve tube cytoplasm, decreases the water potential
-therefore water moves into the sieve cells by osmosis
-this increases the hydrostatic pressure inside the phloem, water moves to decrease their pressure
how do sugars move along the phloem at the sink
-assimilates are actively moved or diffused out of the sieve cells
-this increases water potential so water moves out by osmosis decreasing hydrostatic pressure
why is the xylem waterproof
to stop water leaking through cell
what direction does phloem transport things
upwards and downwards
what is active loading
process of loading sucrose into the sieve tube elements
what happens in active loading
-H+ ions are pumped out from the companion cells to the surrounding leaf tissue creating a diffusion gradient of H+. companion cells have high concentration of Hydrogen ions
-H+ ions diffuse back into the companion cells through cotransporter proteins bringing sucrose with them
-high concentrations of sugar in companion cells cause sucrose to diffuse in to the sieve tube elements
