3.3 Transport In Plants Flashcards
What do dicotyledonous plants have?
- two cotyledons ( organs ) - food stores
- transport vessels in the stems, roots/ leaves ( made of vascular tissues )
What does the xylem vessels do?
- they transport water in the roots, stem and leaves of the plant.
- one direction roots to shoots
What do the phloem vessels do?
- they transport organic molecules ( sucrose ) and can happen in all directions
What are phloem and xylem vessels organised in?
Vascular bundles
How are the vascular bundles at the root organised?
- the xylem and phloem are found together ( centre )
- Xylem is X shaped
- And the phloem fills in the parts between x shape
- around the phloem and xylem there is a ring of endodermis then a ring of meristem cells
How are the vascular bundles organised at the stem?
- they are found on the outside
- xylem on the middle of the bundle
- phloem on the outside of the bundle
- in between - layer of meristem cells
How are the vascular bundles organised in the leaves?
- they form veins on the leaves
- xylem is above the phloem
why do plants need transport systems? (×3)
• low SA:V - direct diffusion would be to slow
• are large (multicellular) organisms - so have a greater demand for substances - so mist move sub.s quickly
• have high metabolic rate - so require lots of sub.s to be provided & removed quickly - direct diffusion would be to slow to meet metabolic needs
what do xylem vessels transport?
water & (dissolved) mineral ions
what is the role of the xylem aside from transporting substances?
provide plant w/ mechanical strength & support
what do phloem vessels transport? (specific)
nutrients, sugars - sucrose, amino acids
where are the xylem & phloem found in the roots?
they are bundled together in the centre of the root w/ the xylem in the middle (star shaped) & the phloem on the outside
where are the xylem & phloem found in the stem?
• they make up vascular bundles in the stem
• arranged in a ring surrounding the centre of the stem
• xylem on inside
• phloem on outside
• vascular bundles (xylem & phloem) are separated (from each other) by the cambium
where are the xylem & phloem found in the leaves? & what is their function here?
• make up vascular tissue of the leaf (vein)
• xylem found on upper side of vein
• phloem found on under side
• provide support for leavesh
what are the structural adaptations of xylem vessels? (×5)
• are long, continuous, hollow tubes - have no end wall between cells => quick transport
• made of dead tissue
• long empty lumen (no cytoplasm => fast transport
• thickened walls strengthened w/ lignin - provide mechanical strength & support
• lignin contains pits so water –> in & out of lignin/xylem
what 2 types of cells are phloem vessels made up of?
sieve tubes
• companion cells
what structural adaptations do sieve tubes (phloem) have?
• separated by sieve plates - contain plasmodesmata (pores) - allow continuous connection of consecutive cells’ cytoplasm
• contain no nucleus, vacuole, organelles - more space for sub.s
what is the function of companion cells (phloem)? what structural adaptations do they have to aid this function?
provide energy to sieve tubes
• contain lots of mitochondria
[• narrow cell wall - easy diffusion of ATP into sieve tubes]
what is the transpiration stream?
when water is pulled up roots–>leaves due to the water evaporation from leaves and the cohesive forces between water molecules
through what process does water move through a plant?
Osmosis
in which direction does water move through a plant in relation to water potential?
high water potential (e.g. -10) –> low water potential (e.g. -30) (down/across w.p. conc.n gradient)
what are 2 pathways water can take to move from the soil –> xylem (through the roots)
• symplast pathway
• apoplast pathway
where (in a cell) does water move through in the symplast pathway (water = soil –> xylem)?
cytoplasm
outline the process of the symplast pathway (water = soil –> xylem)
1) water moves through cytoplasm
2) cytoplasms between cells = continuous as connect through plasmodesmata
3) water moves cell by cell from roots –> xylem, down a w.p. conc.n gradient
where (in a cell) does water move through in the apoplast pathway (water = soil –> xylem)?
cell walls
outline the process of the apoplast pathway (water = soil –> xylem)
1) water moves through cell walls
2) water moves cell by cell until it reaches the casparian strips in the endodermis layer of the root
3) water moves from the casparian strips –> xylem by the symplast pathway (through cytoplasm) (down w.p. conc.n gradient)
what is the importance/effect of casparian strips for the apoplast pathway (water movement –> xylem)?
• is waxy
• is hydrophobic
• is impermeable to water
• forces water to take the symplast pathway for the last few cells to get to the xylem
transpiration definition
loss of water vapour through evaporation from the upper parts of a plant (leaves)
where is most water lost from in transpiration?
Stomata