Section 4-1•1 way cells maintain homeostasis is

controlling movement of substances across cell membrane•Cells must use energy to transport some substances across cell membrane•Other substances move across cell membrane w/out energy = Passive Transport

Section 4-1Diffusion:

•Movement of sub from area of high [ ] to area of low [ ] by random motion of particles

•Many substances enter/leave cells by diffusing across cell membrane

Section 4-1Osmosis:

•Diffusion of water down its [ ] gradient through a selectively permeable membrane; type of passive transport where no ATP energy is needed

Section 4-13 possible directions of water movement:

• Water moves out: Water diffuses out of cell, cell shrinks; sol’n that causes cell to shrink is hypertonic sol’n

• Water moves in: Water diffuses into cell, cell swells; sol’n that causes cell to swell is hypotonic sol’n

• No net water movement: Sol’n that produces no ∆ in cell volume is isotonic sol’n

isotonic hypertonic hypotonic

Red Blood Cell

Section 4-1Diffusion Through Ion Channels

Protein Ion Channel:•protein channel through which ions can cross cell’s membrane

Section 4-1Facilitated Diffusion

Carrier proteins: •Bind to a specific substance on 1 side of membrane and carry sub across cell mem (Facilitated diffusion) and release it on the other side; no ATP energy needed

Section 4-2Active Transport:

•Transport sub across cell mem against its [ ] gradient; uses ATP energy

Section 4-2Sodium-Potassium Pump:

•Important carrier protein mem pump; transports 3 Na+ out of cell and 2 K+ into cell; uses ATP; important for nerve/muscle cell functioning

Section 4-2•Substances, proteins/polysaccharides, are

too large to be transported by carrier proteins; so, moved across cell mem by vesiclesEndocytosis: •Movement of sub into cell by vesicle

Exocytosis: •Movement of sub out of cell by vesicle

Section 4-2Receptor proteins:

•protein binds to specific signal molecule, enables cell to respond to a signal molecule