Cell Environment
Lab 5
Cell Environment

A water solution that contains
nutrients, waste products, gases,
salts, & other substances surrounds
cells.

External environment of the cell.
Cell Environment

The Plasma membrane separates
the cell’s internal & external
environment.

Selectively permeable – small
molecules can pass through freely,
while larger molecules cannot.
Diffusion



Molecules are in constant motion due to
their kinetic energy.
Molecules move randomly.
Random motion tends to create uniform
mixtures.


Net movement of molecules toward the area
where they are scarce – down the
concentration gradient.
Diffusion allows O2, CO2, & nonpolar
liquids to cross plasma membrane.
Diffusion

Diffusion –
net movement
of molecules
from region of
higher
concentration
to region of
lower
concentration.
http://youtu.be/VY0mZUDvbH4
Osmosis


Water molecules
are small enough
to pass through
the plasma
membrane.
Osmosis is the
diffusion of water
across the plasma
membrane of a cell
from a region of
higher
concentration to a
region of lower
concentration.
http://youtu.be/sdiJtDRJQEc
Tonicity


Solutes are molecules dissolved in a solution.
Tonicity – the relative concentration of solute
(particles), and therefore also of solvent (water)
outside the cell compared to inside the cell.



Hypertonic – solution with higher solute
concentration than inside the cell.
Hypotonic – solution with lower solute concentration.
Isotonic – solution with solute concentration equal to
that inside the cell.
Osmosis

Movement of
water into a cell
creates pressure
– osmotic
pressure.


Can cause cell to
swell and burst.
Cell walls protect
plant cells from
bursting.