Lectuer 12: Plant Transport Mechanism Flashcards
Explain how the following are transported in plants:
- H2O
- carbs
- nutrients in seed
- water is transported from root to shoot
- carbs: during photosynthesis from leaf to other tissues (down)
- in young plants: from storage site (roots/seeds) to shoot (upwards)
In the xylem and phloem active or passive transport?
- xylem: passive mostly
- phloem: active or passive; depends on with or against gradient
Explain what governs water entering and exiting the cell
- direction of h2o depends on pressure potential
- H2O pressure potential is impacted by 2 things: turgor pressure and wall pressure
- turgor pressure: expanding volume of cell pushes the membrane against cell wall
- at equilibrium: osmotic pressure is equal to turgor pressure
Answer the following:
- where is water potential highest and lowest
- where does water enter and exit in a plant?
- what drives the transportation of water in a plant (3)?
- highest: roots; lowest: leaves
- enter: roots; exits: leaf through evaporation
- transport is driven by cohesion tension forces, root pressure, and capillary action
Explain the 6 steps of cohesion tension theory
- concept: is energy expended?
- how is tension created?
- Water vapour diffuses out of the leaf
- Water evaporates inside leaf
- Water is pulled out of xylem
- Water is pulled up xylem
- Water is pulled out of root cortex
- Water is pulled from soil into root
- no energy is expended
- transpiration in the leaves creates tension that pulls water into the roots
In roots, water needs to travel through various tissues (3):
- epidermis
- cortex
- into the vascular tissue
define: casparian strip
- wax coated (suberin; hydrophobic compound) strip that blocks the route to xylem (esp for the apoplastic route)
There are 3 different ways water can enter a plant from the root hair to the xylem. Explain each.
- symplastic route: via plasmodesmata
- transmembrane route: via water channels
- apoplastic route: within porous cell walls; can be blocked by Casparian strip and water must find an alternative route; all ions in soil enter through this route
Why have leaves adapted to wilt?
When water is not replaced fast enough the turgor pressure sinks and leaves wilt. To prevent more water loss, stomata close to limit CO2 intake and photosynthesis.
Gives some examples of how plants have adapted to dry conditions (2)
- trichomes (aka epidermal hairs) slow down water loss
- cactus/CAM/C4 plants open stomata at night to reduce h2o loss
How is sucrose translocated?
- via phloem from source to sink (up and down the plant)
Does translocation occur along or against pressure gradient?
- along
Where is sugar stored (3)?
- leaves, roots, seeds
Explain the composition of the phloem and how phloem sap passes through cell tube elements
- composition: sieve tube elements and companion cells
- plasmodesmata connects the cytoplasm of the sieve tube elements and companion cells
- sap passes through pores in the wall between cell tube elements
Explain how sugar is transported from source to sink (make sure you explain how the phloem and xylem is involved)
- see google doc
When sucrose moves from the companion cell to the phloem is it active or passive transport
- passive; even though it involves channel proteins that form pores
antiporters vs symporters
- both are known as cotransporters; don’t require atp
- antiporters: transport molecules in opposite directions
- symporters: transport molecules in the same direction
How are root hairs important?
- expand surface area to facilitate uptake
The absorption and concentration of nutrients by plants is _____
- active transport
What establishes the electrochemical gradient in a plant
- proton pumps
How do cations and anions enter the plant?
- cations: ion channels
- anions: cotransporters
How does a proton pump differ from ion channels and cotransporters?
requires atp
How are toxic ions kept out of the plant? (ion exclusion); give an example of a toxic ion
- toxic ions are passively excluded
- Na+ is necessary for plants but only in small amounts. plants must keep it out if there is a large amount present in soil
How have some plants adapted to tolerate salts?
- ions can be moved into the vacuole
Why is nitrogen an important element for plants? How is it acquired by plants?
- necessary for amino acids and nucleotides, etc
- absorbed from soil as NO3-, NH4+ (although much exists in the air, only bacteria can convert nitrogen from the air into soluble salt)
- some plants use symbiotic bacteria to acquire nitrogen (example: legumes use rhizobia)
Give the equation of nitrogen fixation
- see google doc
Explain the pink nodules on legumes; Explain the symbiotic relationship between legumes and rhizobia
- Roots of infected legumes form nodules that contain bacteria infected cells - Pink due to leghemoglobin (binds oxygen that would prevent reduction of N2) Mutual benefits: - Plants gain nitrogen - Bacteria gain carbohydrates and costs
How is the process of rhizobia infection on legumes regulated?
- plant secretes flavonoid to attract rhizobia
- Bacteria detect flavonoid
and produce a
nodule formation factor - Nod factor initiates
infection, cell proliferation,
and nodule formation - nod factor: lipopolysaccharide that binds to proteins on root cell membrane
- Bacteria live off nutrients provided by host cells,
produce NH4+ for use by plant
explain the symbiotic relationship between funghi and plants; what are the mutual benefits?
- mycorrhizal fungi digest decaying organic material and provide nutrients to plants (amino acids, phosphate, etc but no energy rich compounds)
- benefits: plants gain nitrogen and phosphate; funghi gain carbohydrates
