physiology Flashcards
osmosis and turgor pressure
hypertonic inside, and lots of water present water will flow towards this direction. Cell will swell until it cant anymore, will pres against cell wall with osmotic pressure. This means cell has high turgor pressure (when high water is around)
If plants hypotonic, the water will flow out and the cell will collapse.
PASSIVE
plasmolysis
contraction of the protoplast of a plant cell as a result of loss of water from the cell. PASSIVE
imbibition
Coming into contact with water and swelling up.
the absorption of one substance by another, in particular the uptake of water by a plant or seed. PASSIVE
active transport
water is passive in plant, others are not passive.
Occurs at cell membrane, either putting into tonoplast or pulling from environment. Req ATP and cellular transport channels
Driver is the proton pump by pumping H+ out of cell, up a gradient.
Potassium is needed in the cell, higher than sodium level in the plant. Potassium goes down charged gradient from + to - to get into cell.
Nitrate is - charged, so natural tendency is to leave the cell. Will bring in nitrate if H+ is attached.
Will take in sugars through a co-transport system, brings in sugar if attached to H+
Living osmotically in unfavorable environments
Ex: black mangrove, saltbrush, salicornia
fill tissues with amino acids so that sodium wont pass inside osmotically, so still hypertonic to the saltwater around them.
salicornia (pickle weed): concentrate in one spot and then get rid of that spot of the plant
water route in evapotranspiration
main route in which water moves through plant, water comes into roots via root hairs through cortex, goes through endodermis, gets into xylem tissue and goes up through xylem, root, stem, branch, vascular bundles in leaves and evaporates through stomata.
what the water is used for
- kepps cells supplied
- raw material for photosynthesis
- capture CO2
- cooling plant
how much water is involved in evapotranspiration
- a lot
- avg birch 50 gall x 4 a day
- olive tree about 50 gall a day, but can get by with about 5 gall a day
- every 1 kg of organic material, about 500 kg of water
what process moves the water up through the plamt
- almost entirely a passive process
- 10x better than a “perfect pump”
- takes place mostly in dead cells (xylem)
ideas about how trees sucking up water works
- capillary action (charged water will pull up), smaller tube you have, can pull up water a lot
- root pressure (pericycle transports water to xylem, cells which causes pressure and water to rise, like guttation)
both of these are only good for a few meters
- cohesion tension theoruy
cohesion tension theory
- strong cohesion of water together, start at the top of a plant, water evaporates through stomata. get a meniscus in the corner of the cells, causes a (tension) pull of water out of the cell adjacent because air spaces not smooth.
- water film on spongy mesophyll shrinks
- meniscus draws water from mesophyll cells
(cohesion causes tension)
evaporation through leaf stomata
transpiration
- water potential of cell goes down, drops to lower of the cell next to it.
- water drawn from xylem in leaf vein
- water pulled up molecule by molecule through xylem
water passage into root:
- epidermic root hairs are water permeable, water passively enters into cell
- apoplastic (not entering cytoplasm), or symplastic route
- only symplastic at endodermis
- active transport of K+ in pericycle
evidence supporting cohesion-tensio
- transpiration best at low humidity, open stomata
- negative pressure in xylem
- plant stems contract during transpiration
- captivation “pops” in xylem during transpiration
problems with cohesion-tension
- water is not as cohesive as is needed
- requires extreme negative pressures in xylem
- captivation should cause irreversible embolism
- many trees function near cavitation limit (areas where not much water)2
Alt model: compensating pressure
- living phloem and rays near xylem, which have positive pressure
- root pressure and evaporation work as in other model
- live cells provide static pressure to xylem
- after cavitation, water from live cells repair embolism
supporting evidence for compensating pressure model
- flash freezing shows many embolized tracheids/vessels
- embolism highest in morning, repairs in afternoon
- sugars are in phloem, starches to sugars in rays
- micrographs
