plant transport Flashcards
roots (vb)
vascular bundle located in the centre - withstand strong pulling forces
stem (vb)
vascular bundle located around the edge - provide strength and support
leaf (vb)
the midrib is the main vein carrying the vascular tissue
xylem structure
- dead cells forming long hollow tubes
- cells/columns fused end to end
- lignified walls to withstand high pressures, support the vessel and prevent it from collapsing
- bordered pits allow water movement between vessels
- no nucleus or cell contents - doesn’t impede water transport
- narrow tube
spiral lignin in walls - allows xylem to stretch
contains supportive fibres
phloem structure
- live cells forming long hollow tubes
- sieve tubes joined end to end
- between cells, there are sieve plates/ perforated walls
- thick walls
- sieve tube elements have no nucleus and little cytoplasm to allow more space for mass flow
- sieve plates allow assimilates to move between elements and provide protection
- companion cells; lots of mitochondria, dense cytoplasm, ribosomes, proteins and a large nucleus
LOTS of ATP production
contains supportive fibres
transpiration
loss of water from leaves (stomata)
transpiration stream
the pathway by which water moves into the plant, from the roots to the leaves and out of the plant
apoplast pathway
a route which facilitates the transport of water and solutes across an organ - leaf
- water passes through intracellular spaces and moves by mass flow due to cohesive forces between molecules
symplast pathway
a route which facilitates the transport of water between cells via plasmodesmata
- water enters a cell through the membrane
- water passes through plasmodesmata to neighbouring cells
vacuolar pathway
same as symplast but water can pass through vacuoles too
water uptake
- root hair cells absorb water
- water moves across root cortex to endodermis
- water enters the symplast pathway because the Casparian strip in endodermis blocks apoplast pathway
in the cytoplasm, proteins pump mineral ions from the cytoplasm into the medulla and xylem, creating a more negative water potential in the medulla and xylem. this causes water to move from the cortex into the medulla and then xylem by osmosis.
translocation
transport of assimilates through the plant via the phloem vessels using energy
water up the stem
root pressure, caused by the movement of water from the endodermis and cortex into the medulla, causes water to move into the xylem and forces water upwards.
water lost in the leaves must be replaced by water in the xylem. there is cohesion between molecules so as water is lost, entire columns of water are pulled up in chains
xerophytes
dry conditions
- marram grass thick waxy cuticle dense spongey mesophyl - fewer spaces for H2O sunken stomata curled leaves
- cacti
spines - reduced SA
succulents - store H2O in stem
widespread roots
hydrophytes
wet conditions
- water lilies air spaces stomata on the upper surface stem has spaces hydathodes at leaf tips
