transport in plants Flashcards
features of xylem
-carries water and minerals from roots to photosynthetic parts of plant
-movement always upwards
-long tubular xylem vessels main functional units of xylem
features of phloem
-living tissue
-made of phloem cells that transport dissolved product of photosynthesis from leaves to where its needed for growth or storage as starch
-flow up and down within a plant
whats the cambium
layer of unspecialised cells that divide giving rise to more specialised cells that form both xylem and phloem
first xylem formed
protoxylem
features of the protoxylem
capable of stretching and growing because walls not fully lignified
how does the protoxylem strengthen
-cellulose microfibrils of xylem vessels laid down vertically in stem increasing strength of tube and allows it to withstand compression forces from weight of plant pressing down on it
what happens as the xylem stem ages and the cell stop growing
-increasing amount of lignin are laid down in the cell walls
result of increase in lignin in protoxylem developing
-the cells become impermeable to water and other substances
-tissue becomes more strong and supportive but contents of cell die
metaxylem
increased lignified tissue
what happens after metaxylem is produced
-the end walls between the cells largely break down so the xylem forms hollow tubes running from roots to the tip of stems and leaves
how does water move out of xylem into surrounding cells
role of lignified xylem vessels
very strong and play important supportive role in stems of plants, particularly larger plants
what supports smaller non woody plants
-from turgid parenchyma cells and schlrenchyma and clychryma cells
how can shoot in dye be evidence for water transport through xylem
if you cut end of shoot placed in eosin dye, the dye can be seen carried into transport system into vascular tissues of xylem
how would removing a complete ring of bark give evidence for water transportation in plants
destroys living phloem cells but not xylem cells
-eosin dye placed in water shows upward movement of water through plant is unaffected
steps of audioradiography
-plant given radioactive labelled version of substance being studied
-radioactive plant taken up in same way by plant as normal isotope
-tracked with photographic film, labelled substance causes photographic film to shadow revealing areas it has accumulated
-labelling can be traced by examining each area of plant seperatly using scintillation counter
what are the sieve tube elements made of
of many cells joined together to make very long tubes that run form the highest shoot to the end of the roots
why to the phloem cell contents remain living
because they do not become lignified
how are sieve plates formed
walls between cells become preforated
what do the phloem contents flow through
the holes in the sieve plates
what happens as gaps in sieve plates form
nucleus, tonoplast and other organelles break down
why do phloem sieve tubes survive
-sieve tubes becomes tube filled with phloem sap and mature phloem has no nucleus
-survive because of companion cells
features of companion cells
very active cells
-linked to sieve tube elements by plasmodesmata
adaptations of companion cells
have many infoldings that increase the surface area over they can transport sucrose into cell cytoplasm
-have mitochondria to supply ATP for Active transport
