Transcript How do materials move across the cell membrane?

Movement into and out of the
Cell
Diffusion: the main method by which
small molecules move across the cell
membrane. Molecules move from an
area of higher concentration to lower
concentration.
Osmosis is the diffusion of water
molecules.
How do materials move across
the cell membrane?
By Osmosis and Diffusion
Selectively Permeable
Some substances can pass through the
membrane while others can not.
A cell membrane is selectively
permeable.
The Big Ideas
Some materials move by diffusion.
Some transport requires energy.
Cell size affects transport.
Diffusion
Diffusion occurs when molecules spread out
until they are evenly mixed.
Molecules move from areas of higher
concentration to lower concentration.
Small molecules diffuse through membranes
during passive transport: materials move
without using the cell’s energy.
The diffusion of water through a membrane is
called osmosis.
Diffusion
Active Transport
Using energy to move materials through
a membrane.
Necessary for 2 purposes:


Cells need to move materials from a lesser
concentration to a greater concentration.
Cells need to move large molecules.
Molecules move into the cell through
endocytosis and out through exocytosis.
Passive v. Active Transport
Cell Size Affects Transport
All materials needed by the cell must
move across the cell membrane.
It takes longer for a molecule to reach
the center of a larger cell, so it takes
more time for waste to be removed.
If a cell grew too large, it could not
function well enough to survive.