Transport
Passive and Active
Passive Transport
Passive transport is any transport that occurs
without the use of energy.
 Ex:

Diffusion
 Osmosis
 Facilitated diffusion
 Ion Channels

Diffusion
The movement of molecules
from an area of higher
concentration to an area lower
concentration.
 Concentration gradient
 Driven by kinetic energy
 Dynamic equilibrium
 CO2 and O2

Osmosis

The process in which water molecules diffuse from areas of higher
concentration to lower concentration.

Depends on the concentration of the solutes found in the water on the
two sides of the membrane.
Isotonic
When the
concentration of
solutes outside and
inside the cell are
equal, the outside
solution is said to be
isotonic to the cell.
 The water moves
into and out of the
cell at even rates.

Iso- equal / the same
Hypotonic
When the concentration of
solute is lower outside of
the cell than the
concentration of solute
inside the cell. The solution
outside the cell is said to be
hypotonic.
 The water will move into the
cell until equilibrium is
reached.

Hypo – under /
beneath
Hypertonic
Hyper – above /
excessive
When the concentration of
solute is higher outside of
the cell than the
concentration of solute
inside the cell. The solution
outside the cell is said to be
hypertonic.
 The water will move out of
the cell until equilibrium is
reached.

Cells and Osmosis




Contractile Vacuole – organelle
that takes up water from the
cytoplasm and then pump it out of
the cell. Requires energy.
Turgor Pressure – pressure that
water molecules exert against the
cell wall.
Plasmolysis – When plant cells
do not receive enough water and
the cell membrane shrinks away
from the cell wall. The plant cell
shrivels.
Cytolysis – When animal cells
are left in hypotonic solutions,
water continues to enter until the
cell bursts.
Tonicity

Tonicity problems let you figure out how
water will diffuse based on the %
concentration of a solution.

Ex:

If the solution in a cell is 2%
solute, it would be 98% water.
That cell is placed in a solution
that was 5% solute and
therefore 95% water.
 Is the solution that the cell is
placed in hypotonic, isotonic,
or hypertonic?
 Is the cell going to gain or
lose water?
 If the cell is an animal cell,
what would the cell look like
after it sat in the solution for
an extended period of time?
Facilitated Diffusion and Ion
Channels


Facilitated diffusion – movement of
molecules across a membrane with
assistance from proteins in the
membrane. Energy is still not being used.
 Performed by carrier proteins (type of
integral protein)
 Aid in movement from higher
concentration to lower concentration
regardless of movement into or out of
the cell.
 Glucose uses carrier proteins
Ion Channels




Transport ions from higher concentration to
lower concentration
Na+, K+, Ca2+, and ClSpecific for each ion
Gated
Active Transport
Movement of molecules from
lower concentrations to
higher concentrations with
the use of energy.
 Ex:

Cell Membrane Pumps
 Movement in vesicles (small
spherically shaped sacs
surrounded by a single
membrane)

 Endocytosis
 Exocytosis
Cell Membrane Pumps

Carrier proteins that use energy to “pump” molecules from one area to another.

Use energy – ATP (Adenosine Triphosphate)

Ex : Na+ /K+ Pump

Need a higher concentration of Na+ outside the cell
and a higher concentration of K+ inside the cell.

3 Na+ bind to the pump inside the cell, the pump expels them outside of the cell. This
builds up a high concentration of Na+ outside the cell.

The pump then binds 2 K+ located outside the cell and pushes them through the
membrane into the cell.

This creates an electrical gradient across the cell
where the inside of the cell is negative in
comparison to the outside.
 Allows for the sending and receiving of electrical impulses across the cell.
Na+/K+ Pump
13
Endocytosis
When substances are brought
into the cell
 There are two types

Pinocytosis - small particles
and fluid
 Phagocytosis - large particles
or entire cells

 Used
by cells as a way to eat
 Used by the immune system to
take in bacterial cells and dead
tissues/debris to be destroyed by
the lysosome
Exocytosis
The process by which the
cell exports materials out of
the cell.
 Items for export are first
packaged in the Golgi
apparatus
 Releases items such as:
proteins, hormones,
waste, or toxins
