Osmosis

Transport mechanisms

Passive transport (doesn’t require energy) Diffusion Facilitated diffusion Osmosis Filtration

Active transport (uses energy from ATP)Active transportBulk transport

} Movement down a concentration gradient

3. OsmosisDiffusion of water molecules

through a selectively permeable membrane,

from an area of high water potential

to an area of low water potential

NB: Water potential gradient is opposite to solute concentration gradient.

High water potential = low solute concentration

Concentration Gradient

Water Potential Gradient

Membrane is impermeable to large sugar moleculesbut permeable to small water molecules

Selectively permeable membrane

H2O

Why is OSMOSIS important for living organisms?

• Osmo-regulation - maintaining the right levels of water in cells is vital for life.

• HOMEOSTASIS – maintain balance / equilibrium

• Water moves between cells in a multi-cellular organism

Water balance

COPY

Passive transport

• http://www.youtube.com/watch?v=sdiJtDRJQEc&feature=related (osmosis, 1 min)

• http://www.youtube.com/watch?v=JShwXBWGMyY (passive transport, 5 min)

Transport mechanisms

Passive transport (doesn’t require energy) Diffusion Facilitated diffusion Osmosis Filtration

Active transport (uses energy from ATP)Active transportBulk transport

} Movement down a concentration gradient

2. Active transport

• Uses chemical energy from ATP

• Move molecules against the concentration gradient (low conc. high conc.)

Tonicity is a relative term

• Hypotonic Solution - lower concentration than another solution

• Hypertonic Solution - higher concentration than another solution

• Isotonic Solution - both solutions have same concentration

Shriveled

TurgidFlaccidPlasmolysed

Normal Lysed

HYPOTONICISOTONICHYPERTONIC

ANIMAL CELL

PLANTCELL

ISOTONIC HYPERTONIC HYPOTONIC

NORMAL EXPANDEDSHRIVELED