Energy drives movement Plant Physiology UNI 2006

2 connecting rooms Low energy kidsHigh energy kids

Energy difference Low energy kidsHigh energy kids

Energy difference drives movement NET movement from high energy side to low energy side

Water potential, water movement and cells

2 cells—look at water in cells PP WP Low water potential (high solutes, = pressure) High water potential (low solutes, = pressure)

Membranes select what moves Walls determine volume High solute concentration Low solute concentration P P Solutes can’t move across membrane so solute concentration doesn’t change But water can but walls prevent major volume change WP

Water moves--start Low water potential (high solutes, low pressure) High water potential (low solutes, high pressure) WP PP

PP Water moves--middle (all at the same time) P P WE Water potential increases Pressure increases Pressure decreases Water potential decreases

PP PP Water moves--end WP Water potential increases Pressure increases Pressure decreases Water potential decreases WP WATER POTENTIAL EQUILIBRIUM IS ESTABLISHED

PP At water potential equilibrium WP Pressures NOT equal WP No NET water movement (water movement equal in both directions) Concentrations NOT equal Pressures NOT equal Water potentials are equal

Substances will move From higher to lower energy –Each substance has own independent energy Until equilibrium is reached –Both sides now have = energies for substance Only if there is a route for them to move –Water goes through membranes easily –Solutes cannot (they don’t go to equilibrium) Water potential equilibrium –Solute and pressure forces counterbalance