Learning Outcomes (2-3-4) Flashcards
Diffusion, how is it driven?
Movement of molecules from an area of higher concentration to lower concentration (passive, down the gradient)
driven by the [ ] gradient of molecules, no energy input
Osmosis, is there energy input required?
The movement of water through a selectively permeable membrane from high to low water potential.
no energy input required, based on the [ ] gradient of water, and the water potential
Free Energy
Energy available to do work; in plants, it refers to the potential energy of water.
Chemical Potential
measure of potential energy stored in chemical bonds in plants, influencing water and solute movement.
Water potential
Determines the direction of water movement, combining solute potential (Ψs), pressure potential (ΨP), and gravitational potential (Ψg).
eqn: Ψw=Ψs+ΨP+Ψg
Solute Potential (Ψs) /osmotic potential
Negative, based on [ ] of solute
Pressure Potential (ΨP)
Can be positive (turgor pressure, push or squeeze) or negative (tension, pull or suck).
Gravitational Potential (Ψg)
Significant in tall plants, negligible in small plants.
impact of solutes, positive pressure, negative pressure, and gravity
solutes = lower water potential (free energy)
positive pressure = increases water potential, increase in this adds more pressure and rigidity to cell wall
negative pressure = decreases water potential, results in flaccid plants and less pressure. xylem tension, pulls water upwards
gravity = the taller the plant, the more energy needed to pull water upwards, less overall water potential
how does negative pressure cause a pull of water upwards
- via transpiration, water evaporates through open stomata (guard cells filled with water push them apart to open).
- this lowers water potential
- so this causes a negative pull of water from the soil upwards to re-establish the water potential at the leaves
- water moves up via cohesion-tension theory (cohesion via hydrogen bonds stick water together, adhesion sticks water to the cell wall)
- water moves up continuously in the water column
guttation
at night or early morning, when transpiration is low, there’s still continuous uptake of water in the plant. so, with high water potentail in the root, there’s a positive root pressure that forces water out hydathodes through tips of leaves or cut stems
Apoplast movement
via cell walls
symplastic movement
via cytoplasm and plasmodesmata
location/purpose of casparian strip
- in endodermis
- has suberin/ lignin, impermeable to water and solutes
- forces apoplastic movement into symplastic movement by crossing PM
- acts as a selective barrier to ensure no toxins enter the xylem
- prevents backflow of nutrients and water into apoplastic pathway
what cause root pressure
uptake of ions in root xylem lowers water potential. water moves from soil into xylem, increases water potential and cause positive pressure that pushes water upwards for guttation at night/early morning.
