Transport In Plants Flashcards
What are adaptations of xerophytes and how do they help to reduce water loss
Rolled leaves - traps layer of humid air inside reducing water potential gradient
Hairy Leaves - Traps layer of water vapour reducing water potential gradient
Less stomata - Reduces n. of openings for which water can escape -> reducing transpiration transpiration
Spines instead of leaves - Reduces SA
Where is xylem located in the stem
On the edge and inner part of stem
Where is xylem found in roots
Center of the roots
How does lignified cell wall help xylem with its function
Adds strength to xylem wall and is involved in waterproofing and improves adhesion of water molecules
How is no end plates and no protoplasm on the xylem adapted to its function
Doen not impede the mass flow of H20 and dissolved solutes
How do pits in walls of xylem help xylem with its function
Prevents xylem from collapsing and reduces lateral loss of water
What are the key differences in Xylem and Phloem
Xylem has no living cells wheras Phloem has companion cells
Xylem transports water and mineral ions upwards and is involved in translocation wheras Phloem transports assimilates both ways in the plant
Xylem does not have end plates wheras phloem has sieve plates w/ sieve pores
Xylem is impregnated w/ lignin
How is sieve plates w/ sieve pores adapted to its function
Allows continous movement of organic compounds
What is the function of celluose cell wall in Phloem
Strengthens wall to withstand hydrostatic pressure that moves assimilates
What is the function for no nucleus vacuole or ribosomes in mature cells
Maximises space for the translocation of assimilates
Why are carbohydates not transported in the form of glucose and starch
Starch - Not soluble/ does not affect W.P of cell
Glucose - Less likely to leave S.T.E AND less reactive
What is the first step of how assimilates are loaded into sieve tube elements
H+ moves out of companion cells via active transport which creates a concentration gradient
What happens after Hydrogen ions are actively transported into the cell wall of companion cell
Hydrogen ions move back down the conc. gradient via facilitated diffusion through a cotransporter protein back into the companion cells and Sucrose moves with the Hydrogen Ions
What happens after sucrose is in the companion cells
Sucrose moves into the sieve tube element by diffusion via plasmodesmata
How is sucrose unloaded from companion cells into sink
Sucrose is actively transported out of companion cells out of phloem and to maintain a conc. gradient sucrose is converted into other molecules
Why is transpiration unavoidable
As stomata open for gaseous exchange in order to undergoe photosynthesis to produce sugars
State the steps of transpiration
Water vapour evaporates out of stomata on leaves –> loss of water creates lower hydrostatic pressure at the top of the plant and when water is lost by transpiraton more water moves into xylem down water potential gradient via apoplastic pathway to replace it. There is high hydrostatic pressure at bottom and low H.P at top thus water moces down pressure gradient and is pulled up the xylem under tension by mass flow column of water also pulled up (cohesion & adhesion)
How do the properties of xylem help it move up the transpiration stream
Cohesion occurs / Adhesion occurs (Water sticks to Xylem Wall Vessels)
Water moves up by capillary action
Water acts as a solvent and dissolves sucrose in translocation
State the similarities betwen xylem and phloem
Both are complex tissues
Both are hollow tubes
What are precautions to take when using a potometer
-Cut shoot underwater -> No air enters apparatus -> ALLOWS CONTINUOUS COLUMN OF WATER
-Use syringe to move air bubbles -> No air enters xylem
- Keep shoot still -> Avoid breakage
How to measure transpiration rate
Use potometer, dry leaves and measure distance air bubble has moved per time interval. Calculate vol. of water uptake -> ASSUMPTION - UPTAKE OF WATER = TRANSPIRATION RATE
What is symplast and apoplast pathway
Symplast -> passes along cytoplasm
Apoplast -> passes along cell wall
wat occurs when sucrose is at the sink
Diffuson of sucrose from phloem into surrounding cells
Converted back into glucose (-Used in respiration, converted into starch for storage)
Why does the plant who has increased light intensity require more water
Due to increased rate of transpiration because of more water lost
More stomata open to allow CO2 to enter
