module 3
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
on it to display the answer.
Help!
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| what does the vacuolar pathway have to go through | cell wall, plasma membrane, tonoplast
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| 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
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| what does the symplast pathway have to go through | cell wall and membrane
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| which pathway is the most common and why | apoplast because less resistance
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| why do plants have to have a big surface area to volume ratio | they rely solely on diffusion on gas transport
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| what is the xylem made up of | xylem vessel elements
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| 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
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| why ix the xylem lignified | to support the wall and stop it from collapsing
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| why is deposited in different ways | to give flexibility and stop stem breaking
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| as plants get older what happens to the lignin | it increases
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| why are pits needed | so water can move laterally to other cells
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| how does water get from the soil into the root | osmosis
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| 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
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| how does water move from cell to another | through plasmodesmata (small channels between cells)
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| 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
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| 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
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| how does the water resist gravity when being pulled the xylem | with the use of tension
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| where is the tension needed for water movement come from | from transpiration
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| why does transpiration pull work | water is cohesive due to hydrogen bonds
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| what happens if the cohesion of water in the xylem is broken | water cant carry on up the xylem
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| if a bubble is introduced how does the plant overcome the broken cohesion | water moves laterally to another xylem vessel
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| how does water not fall down the xylem when transpiration is low | it adheres to the walls of the xylem
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| 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)
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| why is transpiration inevitable | stomata are open anyway for photosynthesis so water can evaporate
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| what is transpiration rate affected by | temperature
wind
humidity
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| what are xerophytes | plants that live in hot dry places
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| 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
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| what does a potometer measure | rate of transpiration
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| why is a potometer an estimate | we are assuming all water taken up is transpired
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| 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
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| what are hydrophytes | plants that live in aquatic environments
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| 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
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| what does phloem consist of | sieve vessel elements and companion cells
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| what is the transport of sugars called | translocation
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| 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
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| what is in phloem vessels | cellulose cell wall, plasma membrane, cytoplasm, ER and mitochondria
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| why does phloem only have a small volume of cytoplasm | to reduce resistance
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| whats different about the vacuole, mitochondria and ribosomes of a companion cell | smaller and not centered and mitochondria and ribosomes are larger
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| how are the companion cells connected to the sieve elements | through cytoplasmic strands passing through the plasmodesmata
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| what are sugars called | assimilates
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| what is in phloem sap | large concentrations of sucrose, potassium ions, amino acids, chloride ions, phosphate ions and some other ions
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| why is analysing phloem hard | if sieve element is damaged then pores are blocked with protein then protein replaced with carbohydrate callose
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| where is sucrose loaded into the sieve elements from | the place where it was made/stored this is called the source
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| what happens when sucrose is loaded into the sieve element | water potential is lowered so water follows by osmosis
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| what is the sink | the tissues and organs where sucrose is delivered to
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| 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
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| how does sucrose flow through the phloem | pressure difference between the source and the sink
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| how does sucrose move out of the mesophyll cells to the companion cell | using the apoplast and symplast pathway
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| what moves sucrose into the companion cell | a coprotein found in the membrane
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| where does the energy come from to load the sucrose into the companion cell | from the movement of H+ moving down the concentration gradient
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| process of assimilate loading needs atp | getting the the H+ out of the companion cell
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| how does sugar get from the companion cell into the sieve element | down a concentration gradient through the plasmodesmata
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| what happens to sucrose once in the sink | either gets turned into glucose by the enzyme invertase or into starch
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| 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
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| 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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