Movement of Movement of MoleculesMolecules

Movement across Movement across MembranesMembranes

• All cells must be able to take in and expel various substances across their membranes in order to survive, grow and reproduce

• Cells do this via a number of different processes……

DiffusionDiffusion• Is the net movement of a substance

from a region of high concentration to a region of low concentration.

• Movement occurs down a concentration gradient

• No energy is required.

OsmosisOsmosis• Is the movement of water particles from a

region of high water concentration (low solute) to a region of low water concentration (high solute).

• No energy is required

• Movement occurs down a concentration gradient

Concentration of SolutionsConcentration of Solutions• Hypertonic: has a higher concentration of

dissolved substances than the cell or solution that it is being compared to

• Isotonic: has the same concentration of dissolved substances as the cell or solution it is being compared to

• Hypotonic: has a lower concentration of dissolved substances than the cell or solution that it is being compared to

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

Surrounding Fluid

Animal Cell Plant cell

Isotonic solution Water moves in and out at same rate

Water moves in and out at the same rate

Hypotonic solution Water enters the cell causing it to swell

Water enters the cell and unto the vacuole causing it to swell. The membrane pushes against the cell wall. The cell is turgid.

Hypertonic solution There is movement of water out of the cell. The cell decreases in size.

There is movement of water out of the cell. Cell contents decreases in size. The cell wall keeps the shape. Plasmolysis.

Isotonic Hypotonic Hypertonic

Facilitated DiffusionFacilitated Diffusion• Channel Mediated

Some substances need to move through protein channels in membrane.

• Carrier MediatedSome substances need a protein carrier in addition to a protein channel.

• Neither require energy and both occur down a concentration gradient.

Active TransportActive Transport• Is the movement of substances from

a region of low concentration to a region of high concentration

• Energy is required as movement is against a concentration gradient.

• Carrier molecules assist the movement

Bulk TransportBulk Transport• Endocytosis: bulk transport of

material ______ a cell

• Exocytosis: bulk transport of material ______ of a cell

Question Time!Question Time!

Why do cells need diffusion?Why do cells need diffusion?• For survival…

• Cells obtain nutrients such as oxygen and glucose

• Cells excrete wastes as carbon dioxide and urea

Surface Area: Volume RatioSurface Area: Volume Ratio• The surface area of an object in

comparison to it’s volume.• Important for the movement of

substances• The LARGER the SA:V ratio the

FASTER the rate of exchange.

Why are cells so small?Why are cells so small?• To enhance the rate at which

molecules are exchanged across the cell membrane

• If cells were large diffusion would occur at such a slow rate that the cell would not be able to survive

• So, cells are miniscule

Transport SystemsTransport Systems• Multicellular organisms do not rely on

diffusion alone• Transport systems such as the

circulatory system enables cells to have a ready supply of nutrients and oxygen

• Transport systems also enable an organism to excrete wastes at an efficient rate

Question Time!Question Time!Explain the difference in size between the

Little Penguins on coastal Victoria and the Emperor Penguins from Antarctica. ______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________