Osmoregulation in Plants Flashcards
Osmoregulation
Regulation of solute concentrations and water balance by a cell or organism
Solute
A substance that is dissolved in a solution
Osmosis
The diffusion of (free) water across a selectively permeable membrane, in this case, the plasma membrane
Water potential equation
solute potential + pressure potential
Water potential
Water always moves away from the system with a higher water potential to the system with a lower water potential
Solute potential and concentration
Solute potential decreases with increasing solute concentration
A decrease in solute potential causes a decrease in the total water potential
Can water move directly through the membrane
yes
Can solutes move directly through the membrane
most cannot
Na+ and K+ need their own channels to move through membranes
Turgor pressure
pressure exerted by the protoplast (everything in the cell except the cell wall) against the plant cell wall
Where does water cross the membrane
through the aquaporins
Aquaporin
Integral membrane proteins that form water-selective channels across membrane
Accounts for observed higher rates of water movement than diffusion alone
Advantages of aquatic life
- Buoyancy
- Abundant water
- moderate temperatures
- Filtered light
Obstacles of transition to land
- No buoyancy
- Scarce water
- Extreme temperatures
- Excess light including UV
How did plants respond to water deficit
- increase root growth
- decrease shoot growth
- decrease in transpiration
- decrease in photosynthesis
Osmotic adjustment
A biochemical mechanism that helps plants acclimate to dry or saline/salty soil
While some plants are highly sensitive to water stress and will dehydrate (wilt), others can endure dry or saline conditions without loss of turgor pressure
Extracting water from the soil
A plant root must establish a water potential gradient so that water flows towards the cells of the root from the soil
Water potential must be lower in the rot than in the surrounding soil
Solute potential
- A solution is directly proportional to its molarity
- Aka osmotic potential
- 0 for pure water
- Decreases with addition of solutes
Pressure potential
Physical pressure on a solution
Drought tolerant plants and osmotic adjustment
They regulate their solute potential to compensate for temporary or extended periods of water stress
Results from a net increase in the number of solute particles in the plant cell
By adding solutes to the cell and decreasing plants solute potential…
…osmotic adjustment can drive root water potential to values lower than soil water potential, thereby allowing water to move from soil to plant down a potential gradient
How does the accumulation of solutes affect flow of water
As the cell actively accumulates solutes, water potential drops, promoting the flow of water into the cell
Using osmosis to control stomatal openin
Changes in turgor pressure inflate or deflate guard cells, changing stomata size
What is guard cell turgor pressure controlled by
Controlled by regulation of K+ movement
If isolated plant cells with a water potential averaging -.05 MPa inside the cells are placed into a solution with a water potential of -0.3 MPa, which of the following would be the most likely outcome?
Water would move into the cells
