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transport systems in plants (transport systems in dicotyledonous plants…
transport systems in plants
need for transport systems
metabolic demands
many internal and underground parts of a plant do not photosynthesise
need oxygen and glucose transported to them and waste products of cell metabolism removed
hormones need transporting to areas where they have an effect
mineral ions absorbed by roots need transporting to all cells
make proteins required for enzymes and cell structure
size
need effective transport systems to move substances up and down from roots to leaves
surface area:volume ratio
leaves have large SA:V ratio for exchange of gases
plants have small SA:V ratio when stems and roots are taken into account
cannot rely on diffusion alone to supply cells with essential substances
transport systems in dicotyledonous plants
series of transport vessels running through stem, roots and leaves
vascular system
2 main transport vessels - xylem and phloem
transport tissues arranged in vascular bundles in leaves, stems and roots
stem
vascular bundles around the edge
give strength and support
roots
vascular bundles in the middle
help plant withstand strains of the wind
leaves
midrib of leaf carries vascular tissue through the organ
supports structure of leaf
small branching veins spread through leaf - transport and support
xylem
structure
non-living tissue
materials flow from roots to shoots and leaves
made up of mostly dead cells
xylem vessels - long, hollow structures
several columns of cells fusing together end to end
xylem parenchyma
pack around xylem vessels
store food
contain tannin - bitter chemical protecting plants from attack by herbivores
xylem fibres
long cells with lignifies walls
lignin - can form rings, spirals or solid tubes with small undignified areas
water leaves xylem through bordered pits
provide extra mechanical strength
function
transport of water and mineral ions
support
phloem
structure
living tissue
material can flow up or down the plant
sieve tube elements
many cells joined end to end
long, hollow structure
not lignified
sieve plates
areas between cells where walls become perforated
allow phloem contents to flow through
as these appear - tonoplast, nucleus and other organelles break down
phloem becomes tube filled with phloem sap
mature phloem cells have no nucleus
companion cells
linked to sieve tube elements by plasmodesmata - microscopic channels through cellulose cell walls linking cytoplasm of adjacent cells
maintain all their organelles
very active cells
function as life support system for sieve tube cells
function
transports food in the form of organic solutes around the plant from the leaves
supplies cells with sugars and amino acids needed for cellular respiration and synthesis of other useful molecules