transport tissues Flashcards
(39 cards)
what are companion cells
cells that help load sucrose into the sieve tubes
what are sieve tube elements
make up the tubes in phloem tissue that carry sap up and down the plant. the sieve tube elements are separated by sieve plates
what are xylem vessels
tubes that carry water up the plant
what is xylem tissue
its used to transport water and mineral ions from the roots up to the leaves and other parts of the plant
what does xylem tissue consist of
- vessels to carry the water and dissolved mineral ions
- fibres to help support the plant
- living parenchyma cells which act as packing tissue to separate and support the leaves
what is the structure of a xylem vessel
- the end walls and contents of the cells decay leaving a long column of dead cells with no contents
what happens as xylem vessels develop
lignin impregnates the walls of the cells making the walls waterproof
what does lignin do
it kills the cells and strengthens the vessel walls prevent the vessel from collapsing. this keeps vessels open even at times when water is in short supply
what does lignin thickening in the xylem vessel form
patterns in the cell wall
what patterns does lignin form
spiral, annular (rings) or reticulate (a network of broken rings). this prevents the vessel from being too rigid and allows some flexibility of the stem or branch
what happens in areas where lignification isnt complete
it leaves gaps in the cell wall. these gaps form pits or bordered pits
how are the bordered pits arranged and what is their function
the bordered pits in two adjacent vessels are aligned to allow water to leave one vessel and pass into the next vessel. they also allow water to leave the xylem and pass into the living parts of the plant
what are the adaptations of the xylem vessel
- they can carry water and mineral ions from the roots to the shoots and the leaves
- made from dead cells aligned end to end to form a continuous column
- the tubes are narrow so the water column does not bresk completely and capillary action can be effective
- bordered pits in the lignified walls allow water to move sideways from one vessel to another
- lignin deposited in patterns allows xylem to stretch as the plant grows enabling the stem to bend
why does the flow of water not stop in xylem
- there are no cross walls
- there are no cell contents, nucleus or cytoplasm
- lignin thickening prevents the walls from collapsing
what is the role of parenchyma
it packs around xylem vessels, storing food and containing tannin deposits.
what is a tannin
a bitter chemical that protects plants tissues from herbivore attacks
what are xylem fibres
long cells with lignified secondary walls that provide extra mechanical strength but dont transport water
what is phloem tissue
used to transport assimilates (mainly sucrose and amino acids) around the plant.
how is the sucrose transported
its dissolved in water to form sap. its transported from leaves
what does phloem supply cells with
sugars and amino acids needed for cellular respiration and for synthesis of useful molecules
how do materials flow in the phloem
up and down the plant
what does phloem tissue consist of
sieve tubes - made of sieve tube elements and companion cells
how are sieve tube elements arranged
they are lined up end to end to form sieve tubes. they contain no nucleus and very little sap leaving space for mass flow of sap to occur.
what are at the end of the sieve tube elements
perforated cross walls called sieve plates. these perforationd in the sieve plate allow movement of the sap from one element to the next. the sieve tubes have very thing walls
