Cellular Transport

• Figure 6-12Both diffusion and facilitated diffusion are forms of passive transport, as neither process requires the cell to expend energy. In facilitated diffusion, solute particles pass through a channel in a transport protein.

Passive Transport – movement of substances without energy expended

Movement across the Membrane

• Simple Diffusion• Requires NO energy• Molecules move from

area of HIGH to LOW concentration

Diffusion – the movement of a substance from a high concentration to a low.

• Figure 6-11Dye molecules diffuse across a membrane. At equilibrium, the concentration of dye is the same throughout the container.

Diffusion of Liquids

Facilitated Diffusion- is a process of diffusion facilitated (helped) by transport proteins

Osmosis – water transport across a membrane• Hypertonic- solution with more substance

than water concentration

• Isotonic – equal concentration of substance on both sides of the membrane

• Hypotonic – solution with less substance than water concentration

Isotonic Solution

NO NET MOVEMENT OF

H2O (equal amounts entering

& leaving)

Hypotonic Solution

CYTOLYSIS

Hypertonic Solution

PLASMOLYSIS

Osmosis

Osmosis

• For a cell living in an isotonic environment (for example, many marine invertebrates) osmosis is not a problem.• Similarly, the cells of most land animals are bathed in an

extracellular fluid that is isotonic to the cells.

• Organisms without rigid walls have osmotic problems in either a hypertonic or hypotonic environment and must have adaptations for osmoregulation to maintain their internal environment.

Active Transport – requires energy to move molecules across a membrane

•Like an enzyme, a transport protein recognizes a specific solute, molecule or ion. During active transport, the protein uses energy, usually moving the solute in a direction from lesser concentration to greater concentration.

Transport of Large Molecules

• Vesicles• Exocytosis• Endocytosis