D2.3 Water Potential

water potential

D3.2.1 Water as solvent

Universal solvent; many fluids use water. Aqeuous solutions.

Water is polar, slight +/- charges, bond w other water mol.

D3.2.2. Relative solute conc

Hypertonic: solute conc in environment higher than in system, Water: low
Hypotonic: solute low, water: high
Isotonic: solute and water equal to inside cell

D2.3.3 Osmosis water movement

Water moves from hypo → hypertonic solutions; dynamic equilibrium NET MOVEMENT

Water moves from low conc to high conc.

Cell is concentrated: water into cell, cell is not conc: water out of cell

D2.3.4 Deducing isotonic solute conc for plant tissues

mass change or mean length / solute conc: x-intercept

D2.3.5 Animal cell

No cell wall: water move into/out of cell

solute conc in bigger than out; hypotonic; water into of cell; cell swells and bursts as not able to hold pressure, eg. RBC when you drink water

isotonic: no net change, favourable

solute conc in lower than out; hypertonic: water out of cell; cell shrivels up

In humans, kidneys regulate solute concentration of extracellular fluids

D2.3.6 Cell wall

Cell wall; prevents actual change in shape/size

solute conc in bigger than out; hypotonic; water into cell; turgor pressure: push wall

isotonic: no net change in volume or pressure of cytoplasm - have a little bit of turg pres

solute conc in lower than out; hypertonic; water out of cell; gap between cell wall and plasma membrane: plasmolysed, doesnt recover; wilting

D2.3.7 Using isotonic solutions in medicine

Need to use isotonic as otherwise RBC and other cells take up too much water or lose too much; tissues/organs in isotonic solution before placement & venous-fluids.

D2.3.8 Water Potential

Potential energy per unit volume.

φ : kPa, but all relative, not quantitative.

Pure water at STP: 1ATM, 20^oC = φ = 0

Everything else is lower so always negative

D2.3.9 High pot → low pot

Always move from high pot → lower pot: minimize potential energy

Lower water pot = more negative.

Eg. water moves from cell w φ=-200 → -300

lower water pot → the relatively hypertonic part

D2.3.10 components of φ

1. Solute potential: φ_s

More concentrated, more negative φ_s: bc of bond energy

2. Pressure potential: φ_p

Higher pressure: more potential energy water has to move out; ATM=φ_p=0;
Can be both negative and positive; +φ_p= pressure on cell wall: turgid, -φ_p = underhydrate

φ_w = φ_s + φ_p

D2.3.11 Water potential in plant tissue

1. Plant in water; φ_w = 0: water into plant

2. Plant in hypoton sol: φ_solution>φ_plantwater into plant

3. Plant in hyperton sol: φ_solution<φ_plant water out of plant

4. Adjacent cell diff water pot: always move from higher to lower!!! until equal.