TRANSPORT TISSUES IN PLANTS Flashcards
What are vascular bundles? (1)
groups of phloem, xylem and support tissues found in the stems and roots of plants.
how are water and mineral transported in plants? (1)
through xylem tissue.
how are sugars and amino acids transported in plants? (1)
through phloem tissue.
what is the structure of a xylem tissue? (4)
1)dead empty xylem vessels
2)end walls of vessels break down
3)cell walls of vessels lignified
4)cell walls lignified with rings, spirals and in a reticulate manner
what are the adaptions of the structure of xylem tissue? (4)
1)creates a wide lumen for unrestricted water flow
2) creates a long continuous tube for water transport
3)prevents vessels collapsing when contents are under tension
4) allows vessels to be flexible, preventing breakage as the stem moves.
what is lignin? (1)
a complex polymer of phenols used to thicken plant cell walls.
what is the purpose of lignin? (2)
lignin is laid down in the spaces between the cellulose fibres of the cell wall, this makes them stronger but also impermeable so the cytoplasm dies.
what are pits? (1)
areas of the cell wall that lack lignin and so allow lateral transport.
why is lignin thickening important? (3)
the transport of water inside vessels causes a slight reduction in pressure, threatening to cause them to collapse, the thickening of lignin helps to overcome this problem but stems need to be flexible if they are not tot break. therefore the pattern of thickening is often in the form of rings, spirals or networks.
what are the other types of xylem tissues? (3)
-xylem tracheids
-xylem parenchyma
-xylem fibres
what are xylem tracheids? (3)
are similar to vessels but ae narrower and shorter with tapering ends. found in less advanced species where they are the main water carrying tissue. their sloping end walls break down to form continuous tubes as they become lignified.
what are xylem parenchyma cells? (2)
are typical plant cells with no thickening. found among the vessels or tracheids and remain living tissue.
what are xylem fibres? (3)
are narrow, highly thickened dead cells with only a small gap in the centre. found in other parts of plants. their structure means they cannot transport water but are used for support.
what are sieve plates? (1)
perforated end walls of phloem sieve tubes.
what are companion cells? (1)
plant cells with dense cytoplasm connected to sieve tubes in phloem tissue.
what is the plasmodesmata? (1)
channels in adjacent cell walls of plant cells that form cytoplasmic bridges for communication and transport.
describe the structure of sieve tubes. (4)
sieve tubes are elongated living cells with a very specialised structure, as they develop they lose their nuclei and their cytoplasm is restricted to a very thin peripheral layer with few organelles but remain alive. there end walls have sieve pores which form a sieve plate. running through a large lumen are phloem proteins. sieve tubes are connected to their companion cell through plasmodesmata.
what is the role of the companion cell? (1)
they enable the sieve tubes to stay alive and transport materials.
what are the other types of phloem tissues? (2)
-phloem parenchyma
-phloem fibres.
what is the structure of a phloem tissue? (4)
1)sieve tubes have limited peripheral cytoplasm and organelles
2)end walls from sieve platers with sieve pores
3)companion cells and sieve tubes are connected by plasmodesmata
4)companion cells have dense cytoplasm and many organelles
what are the adaptions of phloem tissue? (4)
1) creates space for sugar transport through the cell
2)forms direct connections for transport from one sieve tube element to the next
3)enables the sieve tube to stay alive without a nucleus and with very limited cytoplasm
4)thought to be needed to support sieve tubes
