7) Transport in Plants Flashcards
what is adhesion ?
the formation of hydrogen bonds between carbohydrates in the xylem vessel walls and water molecules
what is cohesion ?
- formation of hydrogen bonds between water molecules.
what is the apoplastic pathway ?
water moves through the intercellular spaces between cellulose molecules in the cell wall
what is the casparian strip ?
waterproof strip surrounding endodermal cells of the root that blocks the apoplastic pathway, forcing water through the symplast route.
what is the symplastic pathway ?
- water enters the cytoplasm through the plasma membrane and moves between adjacent cells via plasmodesmata.
- water diffuses down its water potential gradient by osmosis.
what is the function of the xylem
- carries dissolved minerals and water up the plant
- structural support
- food storage
what is the function of phloem
transport organic compounds (sucrose) from source to the sink
where is xylem and phloem in the roots
xylem : centre of vascular bundle
phloem : on the edges of the centre
where is xylem and phloem in the stems
xylem : inside (closest to centre of stem)
phloem : outside (closest to epidermis)
where is xylem and phloem in the leaves
xylem : upper side (closest to upper epidermis)
phloem : lower side (closest to lower epidermis)
phloem sieve tube adaptations
-cell membranes that retain sucrose & other assimilates within cells
- few cell contents to reduce resistance to flow of phloem sap
- sieve plates to hold sieve tubes together/resist internal pressure
- sieve pores to allow ease of flow between sieve tube elements
adaptations of companion cell
- many mitochondria to provide energy to move solutions into sieve tubes
- many plasmodesmata to allow easy movement of phloem sap into/out of sieve tubes
- pump & co-transporter proteins in cell membranes for absorption of sucrose (from apoplast pathway from mesophyll cells)
- some plasmodesmata shared with mesophyll cells for transport of sucrose via symplast pathway
how is xylem vessel suited to their function
- transport of water & mineral ions
- elongated cells / tubes for transport
- hollow/ no cytoplasm or contents SO more space for greater volume for flow
- cellulose lining SO adhesion of water molecules
- lignified walls to prevent collapse
- lignified walls SO waterproof/prevents loss of water
- pits to allow sideways movement
how does sieve tube element help translocation
- little cytoplasm/no vacuole/no tonoplast
- pores in sieve plate provide little resistance
- sieve plate prevents cell collapsing
- plasmodesmata allows loading
- cellulose walls prevent tm expansion
- mitochondria for ATP for repair
how do companion cells help in translocation
- assimilates (sucrose/amino acids) loaded/pumped
- pumping H+
- co-transport (H+ carry sucrose with them)
- mitochondria provide ATP for active transport