CELL TRANSPORT
• Cell membranes are similar to a mesh bag
or a screen on a window.
What Does This Have To Do
With Cells???
• To survive, cells must take in nutrients and
eliminate waste materials.
• To do this, nutrients and waste materials
must cross the cell membrane between the
solution outside of the cell, and the
solution inside the cell.
What type of Membrane?
• Semi permeable membrane: allows certain
molecules to pass through and prevents
others from passing.
Semi Permeable Cell Membrane
• Small molecules like water can enter and leave
the cell freely.
• Larger molecules such as proteins and
carbohydrates cannot enter and leave the cell
freely due to their size.
Transportation Processes (2)
• Transport = movement of a substance
across a cell membrane
• Passive Transport: without energy.
• Active Transport: uses energy
Passive Transport (3 types)
• Simple Diffusion
• Facilitated Diffusion
• Osmosis
All three involve the movement of a
substance across a cell membrane without the
input of the cell’s energy.
Factors To Consider (2)
• Diffusion always occurs from a high
concentration to a low concentration.
• A concentration gradient is the difference
between the concentration of a particular
molecule in one area and its concentration in an
adjacent area.
• When molecules have been dispersed evenly,
there is no concentration gradient, an equilibrium
has been reached, and diffusion stops.
Simple Diffusion
Initially, the concentration
of a substance outside the
cell is higher than the
inside.
Later, the substance has
diffused into the cell so
that the concentration is
the same on both sides of
the membrane.
If a lump of sugar is dropped into a beaker of
water, the molecules dissolve (A) and diffuse (B
and C).
Eventually, diffusion results in an even distribution
of sugar molecules throughout the water (D).
Facilitated Diffusion
• Molecules diffuse across a cell membrane
with the HELP of carrier proteins in the
membrane.
• Always move from a higher level of
concentration to a lower level.
• Allows the glucose molecule into the blood
cells.
Facilitated Diffusion
During facilitated
diffusion, carrier
proteins shuttle
molecules across
the lipid bilayer of
the cell
membrane.
Facilitated Diffusion
Osmosis
WATER
• The diffusion of water across a semi permeable
membrane
• Again water moves down its concentration
gradient.
• Moves from higher water concentration to lower
water concentration.
Osmosis
Active Transport
Uses cellular energy to move substances
across the cell membrane. Against a
concentration gradient – from a low
concentration to a high concentration.
The Sodium Potassium Pump
• Active transport is especially important in
maintaining the ion concentration in cells.
• Ex: Animal cells pump sodium ions out
and potassium ions into the cell.
• High concentration of sodium ions outside
of the cell.
Sodium Potassium Pump
Exocytosis
• Moves material too big to fit through the
cell membrane from a low concentration to
a high concentration.
• The vesicles then fuse with the cell
membrane and the materials in the vesicles
is secreted out of the cell.
Endocytosis
• The process by which a portion of the cell
membrane surrounds a desirable
macromolecule that is outside of the cell.
Moves from a low concentration to a high
concentration.
• The cell then pinches off the saclike
portion of its outer membrane to form a
tiny new vesicle.
Desired macromolecules
Three tumor cells being engulfed by a white
blood cell!