transport in plants Flashcards
why do plants need to acquire nutrients?
- photosynthesis and cellular respiration
- sugar/energy production
- building blocks for organic molecules (b/c they don’t ingest)
where do plants preform gas exchange?
- roots
- stomata
- lenticels
3 main functions of roots
- anchor plant
- absorb water and minerals
- store carbohydrates
what are/the function of root hairs?
- extension of root epidermal cells
- increase surface area of roots
- account for most water and mineral absorption
what are lenticels, what are their function?
- holes in periderm
- connect outside air to living stem/root cells
- allow for gas diffusion (because bark in impermeable to gas/water)
how does leaf structure aid in gas exchange?
- increased surface area via leaf shape and branching
- easy access to vascular tissue and transport cells
- thick cuticle to protect from water
what is the structure that allows for gas exchange in leaves, where are they found?
stomata -> small openings in leaf
- found on bottom of leaf
- responsible for 95% of water loss in plants
how do stomata open and close, what are the cells involved, how do they move?
- 2 guard cells on either side of stomata control the diameter of the stoma by changing shape
- change shape (open/close opening of hole) by turgor pressure
- cells actively pump potassium in –> become turgid by water movement (water moves to where there is more solute), makes cells firm and open hole to stomata
- when cells stop pumping potassium in, water movement stops, cells become flaccid (tugor pressure declines), and hole between guard cells closes
how do guard cells keep their bean shape?
- uneven thickness of walls
2. cellulose microfibrils in cell wall cause guard cells to buckle outward (like support ties)
why do stomata close at night?
to prevent water loss while plant is not photosynthesizing
what are cues for stomata opening/closing?
- light (blue-light receptors)
- depletion of CO2 (indicates photosynthesis has begun and needs more CO2 to continue)
- circadian rhythm
why might stomata close during the day?
may close if water loss is greater than water gain
1. drought
2. high temperature
3. wind
suffer from loss of turgor pressure in guard cells, ie not enough water to keep them rigid
what is the crypt?
dug out that stomata and guard cells sit in to protect them from the wind
4 adaptations of xerophytes (plants that live in arid conditions)
- no leaves during drought -> may produce little leaves after rain to help with photosynthesis
- can photosynthesis through stem
- very thick cuticles
- leafs mods that help reduce transpiration
what is water evaporation in plants called?
transpiration
what is bulk flow?
movement of fluids driven by pressure; efficient long distance transport of fluid
after root hairs absorb water and minerals, what are the 2 routes for it to get to the vascular tissue?
- Apoplast Route
2. Symplast route
what are plasmodesmata?
little channels that connect the cytoplasm of cells and allow for movement between cells
what is the apoplast?
the continuum of cell walls and extracellular spaces
what is the Symplastic route?
route water/minerals can take from cell to cell via the continuum of cytoplasm via plasmodesmata
what is the Apoplastic route? why is this more “dangerous” for the plant?
route of water/minerals in between cells, via cell walls and extracellular spaces. more dangerous for the plant because it has no control over what substances are being transported through it, vs in symplastic route where the cells are selectively permeable and only certain things are let in
what is the endodermis? what does it do/why is it important? why is it important in reference to the apoplastic route?
endodermis is the innermost layer of cells in the root cortex, which surrounds the vascular cylinder
- it regulates the up take of minerals, and is the last checkpoint for products entering the vascular system
- all water and minerals must pass through these cells
- it is important because it controls what the plant takes into its circulatory system.
- important in reference to apoplastic route because it is a filter for things that have not yet been filtered because of moving outside of cell walls
what is the waxy casparian strip?
strip that blocks apoplastic transfer between endodermis cells, and forces all materials to go through the cell membranes of endodermis cells
what are the 2 methods that move xylem sap?
- pushing via Root pressure
2. pulling via transpiration cohesion-tension mechanism
what is root pressure?
- positive pressure (push)
- at night (when transpiration is low) root cells continue to pump mineral ions into xylem; water flowing into xylem creates root pressure (b/c can’t go back out through endodermis) = push of xylem sap
what is guttation
the exudation of water droplets on tips or edges of
leaves because of root pressure
what is the Transpiration Cohesion-tension mechanism?
- Water vapor in leaf diffuses down its gradient and exits the leaf via stomata
- Transpiration produces negative pressure (tension) in the leaf, which exerts a pulling force on water in the xylem, pulling water into the leaf
= pull of xylem sap (negative pressure)
how can the transpiration cohesion-tension mechanism work?
because of the unique properties of water
1. water has a charge
2. the attraction between water molecules are strong
this makes water want to stay together, which is how transpiration is able to pull water from the root, to the leaf
what are 5 factors that can affect transpiration?
- available light
- temperature
- availability of water
- humidity
- air movement
bulk flow vs diffusion
bulk flow: 1. driven by differences in pressure 2. occurs in hollow cells 3. moves entire solution 4. much faster diffusion: 1. driven by difference in solute concentration 2. occurs across cell membranes 3. moves just water or just solute 4. much slower -no energy cost for either bulk flow or simple diffusion
route that water takes through plants
soil -> root hairs root hairs -> endodermis via: 1. apoplastic route (btw cells) hits waxy casparian strip 2. symplastic route (cell to cell) endodermis -> xylem xylem -> leaf via: 1. root pressure 2. transpiration cohesion-tension mechanism leaf -> stomata
what is phloem sap?
aqueous solution high in sucrose + amino acids, minerals and hormones
where does phloem sap travel to and from, what are these called, what are they?
phloem sap travels from a sugar source to a sugar sink
source: organ that produces sugar
eg. mature leaf
sink: organ that consumes or stores sugar
eg. bulb, growing roots and buds
what is translocation?
process where phloem transports phloem sap (products of photosynthesis) throughout plant
route of sugar in plant
-sugar created in photosynthetic mesophyll cells (source cells)
1. sugar loaded into sieve-tube elements either directly or by companion cells from source cells via:
-apoplastic route
-symplastic route
may or may not need active transport to pump sugar into phloem
2. because increase in sugar in sieve-tube, water follows by osmosis, creates positive pressure (push) of bulk flow, which transports phloem sap throughout cell
3. sugar unloaded at sink cells
4. now have a higher water concentration in sieve tubes and it is absorbed and recycled back into surrounding cells and xylem
why does sugar movement into phloem require active transport?
In many plants, sugar movement into the phloem requires active transport because sucrose is more concentrated in sieve-tube elements and companion cells than in mesophyll (soucre cells). Proton pumping and H+/sucrose co-transport enable sucrose to be actively transported from source cells to sieve-tube elements or companion cells
why do plants die if you over water them?
Plants die if you over water them because it limits or cuts off the supply of oxygen to the roots. The roots take up oxygen that is held between the soil, so if it is completely saturated in water, there is no oxygen for the roots to access.
which layer in leaves is responsible for most of the photosynthesis that occurs? what kind of tissue is this?
the palisade mesophyll layer
-this is ground tissue (parenchyma)
what is the other kind of mesophyll layer (not the photosynthetic one), what is it called, what is its function?
- spongy mesophyll
- allows for movement of gasses (CO2) in leaf
why are root hairs important? how does water move into root hairs?
-because they increase the surface area of roots, most water and mineral absorption occurs near
root tips
-water moves by osmosis
what is the symplast?
cytoplasmic continuum connected by plasmodesmata
