Question | Answer |
what does the vacuolar pathway have to go through | cell wall, plasma membrane, tonoplast |
what does the apoplast pathway have to go through and what mechanism is used for the water to flow | non-living parts-cell wall and by mass flow |
what does the symplast pathway have to go through | cell wall and membrane |
which pathway is the most common and why | apoplast because less resistance |
why do plants have to have a big surface area to volume ratio | they rely solely on diffusion on gas transport |
what is the xylem made up of | xylem vessel elements |
what are the adaptions of the xylem vessel elements | there are no end walls- allows water to pass continuously
no cytoplasm- (they are dead) no resistance
partially lignified- to strengthen but have parts with no lignin called pits that water can move laterally through |
why ix the xylem lignified | to support the wall and stop it from collapsing |
why is deposited in different ways | to give flexibility and stop stem breaking |
as plants get older what happens to the lignin | it increases |
why are pits needed | so water can move laterally to other cells |
how does water get from the soil into the root | osmosis |
what causes the osmosis to occur from the soil to the root | nitrates and minerals are taken in by active transport and this decreases the water potential in the root |
how does water move from cell to another | through plasmodesmata (small channels between cells) |
why does the water have to stop using the apoplast pathway when it reaches the endodermis | it encounters waterproof layer called the casparian strip which contains suberin that is water proof |
why is the casparian strip needed | water carries minerals and with the apoplast pathway you cant control what enters the xylem but if you force the water through a partially membrane you can control what enters the xylem |
how does the water resist gravity when being pulled the xylem | with the use of tension |
where is the tension needed for water movement come from | from transpiration |
why does transpiration pull work | water is cohesive due to hydrogen bonds |
what happens if the cohesion of water in the xylem is broken | water cant carry on up the xylem |
if a bubble is introduced how does the plant overcome the broken cohesion | water moves laterally to another xylem vessel |
how does water not fall down the xylem when transpiration is low | it adheres to the walls of the xylem |
name two other ways apart from transpiration pull that water can move up the xylem | capillary action and hydrostatic pressure (mass flow from high pressure to low pressure) |
why is transpiration inevitable | stomata are open anyway for photosynthesis so water can evaporate |
what is transpiration rate affected by | temperature
wind
humidity |
what are xerophytes | plants that live in hot dry places |
how are xerophytes adapted to their environment | small/less stomata
rolled leaves
stomata on underside
thick waxy cuticle
hairs around stomata
stomata sunken in leaf
small surface area of leaves
high solute concentration in cells |
what does a potometer measure | rate of transpiration |
why is a potometer an estimate | we are assuming all water taken up is transpired |
what should you do when setting up a potometer | cut shoot at an angle
make sure leaves are dry
make sure shoot is healthy
make sure shoot has leaves
make sure rubber tubing is water tight
assemble underwater |
what are hydrophytes | plants that live in aquatic environments |
what adaptions do hydrophytes have | air spaces in leaf-so they can float and as storage for oxygen
stomata on upperside of leaf
flexible stems |
what does phloem consist of | sieve vessel elements and companion cells |
what is the transport of sugars called | translocation |
what are the end plates of sieve elements called and how are they adapted | sieve plates and they have pores in them call sieve pores that allow free movement |
what is in phloem vessels | cellulose cell wall, plasma membrane, cytoplasm, ER and mitochondria |
why does phloem only have a small volume of cytoplasm | to reduce resistance |
whats different about the vacuole, mitochondria and ribosomes of a companion cell | smaller and not centered and mitochondria and ribosomes are larger |
how are the companion cells connected to the sieve elements | through cytoplasmic strands passing through the plasmodesmata |
what are sugars called | assimilates |
what is in phloem sap | large concentrations of sucrose, potassium ions, amino acids, chloride ions, phosphate ions and some other ions |
why is analysing phloem hard | if sieve element is damaged then pores are blocked with protein then protein replaced with carbohydrate callose |
where is sucrose loaded into the sieve elements from | the place where it was made/stored this is called the source |
what happens when sucrose is loaded into the sieve element | water potential is lowered so water follows by osmosis |
what is the sink | the tissues and organs where sucrose is delivered to |
why is the process of sugars moving from the source to the sink passive | it is moving down a concentration gradient and so doesnt need energy |
how does sucrose flow through the phloem | pressure difference between the source and the sink |
how does sucrose move out of the mesophyll cells to the companion cell | using the apoplast and symplast pathway |
what moves sucrose into the companion cell | a coprotein found in the membrane |
where does the energy come from to load the sucrose into the companion cell | from the movement of H+ moving down the concentration gradient |
process of assimilate loading needs atp | getting the the H+ out of the companion cell |
how does sugar get from the companion cell into the sieve element | down a concentration gradient through the plasmodesmata |
what happens to sucrose once in the sink | either gets turned into glucose by the enzyme invertase or into starch |
what is the evidence for mass flow of sucrose | the rate is 10000 faster than just diffusion alone and are similar to those of using a pressure gradient |
what is the evidence for sucrose loading | sap has a high PH plus there is an electrical difference across the companion cell |
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