Plant transport Flashcards
What is the apoplast pathway?
Cell wall to cell wall without entering the cell cytoplasm
What is the symplast pathway?
Moves into the cytoplasm by osmosis across the plasma membrane via the plasmodesmata to the xylem
What is the vacuolar pathway?
Move via vacuoles but has to cross plasma membranes as resistance is to high. Little water is moved
What is the function of the apoplast, symplast and vacuolar pathway?
Move water across a root
What are tracheids?
Dead, tube-like cells with a tapering end
What is the function of tracheids?
Transportation of water and minerals
What four cells does the xylem contain?
Vessels, tracheids, fibres and parenchyma
Where are tracheids mostly found?
In gymnosperm and lower angiosperm
What is the structure of tracheids?
Thick lignified wall. No nucleus or cytoplasm
What is the structure of vessels in the xylem?
Long cylindrical structure with a tube like appearance and lignified walls
Where are vessels mostly found in the xylem?
In angiosperms
What are vessels in the xylem?
Dead, large central cavity and have no cytoplasm or nucleus
What are fibres in the xylem?
Dead cells with a lignified wall and a central lumen
What is the role of fibres in the xylem?
Provide mechanical support
What is the structure of the fibres in the xylem
Dead cell with a lignified wall and a central lumen
What is the role of parenchyma in the xylem?
Assist in the short distance transportation of water and stores starch and fat
What is the structure of the parenchyma in the xylem?
Only living cells in the xylem
What is the cohesion-tension theory of transpiration?
- Water uptake primarily occurs by osmosis from soil into root hair cells
- Moves via symplast/vacuolar pathways as casparian band prevents movement through apoplast pathway
- Water enters xylem via cohesion and osmosis
- Water drawn up xylem through cohesion and adhesion due to the state of tension caused by transpiration
- Water leaves the xylem via vessels (osmosis) into the leaf
- Water moves through the leaf tissues via via the apoplast, vacuolar and symplast pathways
- Water evaporates from surface of epidermal cells and diffuses into the atmosphere
What is cohesion?
Attractive forces between the same molecules
What is adhesion?
Attractive forces between molecules and other dissimilar surfaces or molecules
What is a potometer used to measure?
Rate of water uptake in a leafy shoot
How could a potometer be set up?
Cut healthy shoot under water
Cut shoot at a slant
Check apparatus is full of water
Insert shoot into the apparatus under water
Shut screw clip
Remove potometer from water ensuring airtight joints around the shoot
Why should the shoot be cut under water in a potometer?
Stop air from entering xylem vessels
Why should the shoot be cut at a slant in a potometer?
To increase SA
What should be done while measuring the uptake of water in a leafy plant to ensure the results are valid?
Dry plant leaves
Keep conditions constant
Allow time for shoot to acclimatize
Keep ruler fixed and record position of air bubble on scale
What effect does increased temperature have on the rate of transpiration?
Increases transpiration
What effect does increased humidity have on the rate of transpiration?
Decreases transpiration
What effect does increased air movement have on the rate of transpiration?
Increases transpiration
What effect does increased light intensity have on the rate of transpiration?
Increases transpiration
Why would increased temperature result in increased transpiration?
Increases kinetic energy of water molecules so diffusion occurs quicker
Increases kinetic energy of air and warm air holds more water
Why would increased humidity result in decreased transpiration?
No/less diffusion gradient between the internal air spaces and the environment
Why would increased air movement result in increased transpiration?
Diffusion gradient maintained, as humid air is blown away and fresh air which is
Why would increased light intensity result in increased transpiration?
Affects the degree of opening and closing of stomata
What is the mass flow theory?
Transport in the phloem - movements of water and sucrose generate a gradient of hydrostatic pressure which drives the translocation of organic solutes from leaf (source) to roots (sink)
What happens in mass flow theory?
- Companion cell actively transports H+ into mesophyll cell. Sucrose is co-transported with H+ down the proton gradient back into the companion cell
- Sucrose moves from the companion cell into sieve tube element through the plasmodesmata
- Sieve tube element’s water potential lowers due to the sucrose entering
- Water diffuses into the sieve tube element via osmosis
- Sieve plates reduce the fluid volume
- Water and sucrose move down the phloem via translocation from an area of high hydrostatic pressure to low hydrostatic pressure
- Living cells (parenchyma) in the root actively transport sucrose out of sieve tube elements
- Water diffuses from the sieve tube elements into the xylem vessels
What is the evidence against mass flow theory?
Sieve plates would obstruct mass flow so why are they there?
Sucrose and amino acids have been observed moving at different rates and in different directions in the same tissue
Why are the companion cells in the middle of the stem not just at the source and sink?
How are roots adapted for the uptake of water and mineral ions?
Large SA for water to enter via osmosis
Many root hair cells per root - large total SA
Cellulose cell wall is freely permeable to water
Many mitochondria to provide ATP
Many protein carriers in cells membrane for transport of mineral ions into the cell
How does water and mineral ions enter the root?
Water potential of soil is higher than water potential inside of root
Water enters via osmosis
Ions actively transported into root cell which decreases the water potential inside the cell
Steeper water potential gradient causes more water to move into the cell quicker
What is root pressure?
A constant additional force that influences the upward movement of water
How is tension generated in a plant?
Water molecules are evaporating through the stomata
Cohesion therefore causes tension throughout the plant causing water to rise
What is translocation?
The movement of sugars and other dissolved substances through the phloem
