Water potential and Osmosis

What is osmosis?

The passive movement (diffusion) of water from a region of higher water potential to a region of lower water potential, through a selectively permeable membrane.

What is water potential?

A measure of how free water molecules are to move (their potential to do osmosis).

Which direction does water always move in?

From a high water potential to low water potential, down a water potential gradient.

What's the water potential of pure water?

0

• What does it mean for a substance to be hypotonic to another?

• Solute concentration outside cell= lower

• Water potential outside cell= higher

• Net movement of water= outside to inside the cell

What does it mean for a substance to be isotonic to another?

• Solute concentration outside cell= the same

• Water potential outside cell= the same

• Net movement if water= no movement

• What does it mean for a substance to be hypertonic to another?

• Solute concentration outside cell= higher

• Water potential outside cell= lower

• Net movement of water= inside to outside the cell

What happens to an animal cell in an isotonic, hypotonic and hypertonic solution?

• Isotonic- optimum condition

• Hypotonic- cell may lyse

• Hypertonic- cell undergoes crenation

• What happens to an plant cell in an isotonic, hypotonic and hypertonic solution?

• Isotonic- incipient plasmolysis

• Hypotonic- turgid, optimum

• Hypertonic- plasmolysis

What is plasmolysis?

The cell membrane has detached from the cell wall.

What is incipient plasmolysis?

Plasmolysis is just about to happen.

What is the equation for water potential?

water potential = pressure potential + solute potential