API  Study Guides Home Page

Movement Through a Membrane

Study Guide

Type of Movement

Direction of Movement

Energy Used or Not Used

Unique Points

 

 

Diffusion

HIGH concentration to LOW concentration (down) a concentration gradient

 

Passive Movement

Energy cost = zero

 

No ATP is used

random motion of molecules results in a net movement of across a concentration gradient,

until

dynamic equilibrium is reached

Facilitated Diffusion

 

HIGH concentration to LOW concentration (down) a concentration gradient

 

Passive Movement

Energy cost = zero

 

No ATP is used

Needs a special channel or carrier molecule

 

The ability to cross the membrane is going to depend on the number of carrier proteins.

Osmosis

 

HIGH

concentration of water to LOW concentration of water

Passive Movement

Energy cost = zero

No ATP is used

water concentration differs on both sides and the solute is impermeable to the membrane

Active Transport

From LOW concentration to HIGH concentration

 

REQUIRES ATP

moves molecules in only one direction

Exocytosis & Endocytosis

Concentration gradient does not matter

 

REQUIRES ATP

Exocytosis

inside the cell to the outside of the cell

Endocytosis

outside the cell to inside the cell