Cellular Transport
Notes
About Cell Membranes
• All cells have a cell membrane
• Functions:
a. Controls what enters and exits the cell to maintain an internal balance called homeostasis
b. Provides protection and support for the cell
TEM picture of a real
cell membrane.
What is the purpose of cellular transport?
• Homeostasis depends upon appropriate movement of materials across the cell membrane.
– Required materials must pass into the cells so they can be utilized.
• Ex. Oxygen and glucose for cellular respiration
– Waste materials must pass out of the cells as they are produced
• Ex. The CO2 produced as a waste product of cellular respiration
• The cell membrane regulates the passage of materials into and out of the cell.
– Needed materials move in
– Excess materials move out
How?
• Each individual cell exists in a fluid environment, and
the cytoplasm within the cell also has a fluid
environment. The presence of a liquid makes it
possible for substances (such as nutrients, oxygen,
and waste products) to move into and out of the cell.
• A cell membrane is semipermeable (selectively
permeable), meaning that some substances can pass
directly through the cell membrane while other
substances can not.
• Materials can enter or exit through the cell membrane
by passive transport or active transport.
Membrane
movement
animation
Types of Cellular Transport
• Passive Transport
cell doesn’t use energy
1. Diffusion
2. Facilitated Diffusion
3. Osmosis
• Active Transport
cell does use energy
1. Protein Pumps
2. Endocytosis
3. Exocytosis
high
low
This is
gonna be
hard
work!!
high
low
Weeee!!!
•Animations of Active
Transport & Passive
Transport
Passive Transport • cell uses no energy
• molecules move randomly
• The random motion of molecules occurs
along the concentration gradient meaning
molecules spread out from an area of high
concentration to an area of low
concentration.
• (HighLow) • Three types:
3 Types of Passive Transport
1. Diffusion – is the spreading out of molecules
across a cell membrane until they are equally
concentrated.
2. Facilitative Diffusion – diffusion with the help
of transport proteins
3. Osmosis – diffusion of water
Passive Transport:
1. Diffusion
• Diffusion: random movement of particles from
an area of high concentration to an area of
low concentration.
• Diffusion continues until all molecules are evenly
spaced (equilibrium is reached)-Note: molecules will
still move around but stay spread out.
Simple Diffusion
Animation
• Facilitated diffusion: diffusion of specific particles along the concentration gradient (High Low) with the help of transport proteins found in the membrane
a. Transport Proteins are specific – they “select” only certain molecules to cross the membrane
b. Transports larger or charged molecules that cannot pass through the membrane on their own
c. Glucose is an example of a molecule that passes into the cell through facilitated diffusion
Facilitated
diffusion (Channel
Protein)
Simple
Diffusion
(Lipid
Bilayer)
Passive Transport:
2. Facilitated Diffusion
Carrier Protein
A B
• http://bio.winona.edu/berg/Free.htm
High Concentration
Low Concentration
Cell Membrane
Glucose molecules
Protein channel
Passive Transport: 2. Facilitated Diffusion
Go to
Section:
Transport
Protein Through a
Cellular Transport From a- High
Low
• Channel Proteins
animations
• Osmosis: diffusion of water
through a selectively permeable
membrane
• Water moves from a high
concentration of water to a low
concentration of water
• Because water is so small and in
such abundance, the cell
cannot control its movement
through the cell membrane.
Osmosis
animation
Passive Transport:
3. Osmosis
Effects of Osmosis on Life
• Water moves freely
through pores.
• Solute (green) too large
to move across.
• Reminder:
– Solute: what is being dissolved
– Solvent: what dissolves the solute
• In salt water, the solute is the salt and the solvent is the
water
Hypotonic Solution
Hypotonic: The solution has a lower concentration of
solutes and a higher concentration of water than inside the
cell. (Low solute; High water)
Result: Water moves from the solution to inside the cell): Cell
Swells and bursts open (lyse)!
• Osmosis Animations for isotonic,
hypertonic, and hypotonic solutions
Hypertonic Solution
Hypertonic: The solution has a higher concentration of
solutes and a lower concentration of water than inside the
cell. (High solute; Low water)
Result: Water moves out of the cell into the solution:
Cell shrivels!
• Osmosis Animations for isotonic,
hypertonic, and hypotonic solutions
shrinks
Isotonic Solution
Isotonic: The concentration of solutes in the solution is
equal to the concentration of solutes inside the cell.
Result: Water moves equally in both directions and the cell
remains same size! (Dynamic Equilibrium)
• Osmosis Animations for isotonic,
hypertonic, and hypotonic solutions
In what type of solution are these cells?
A C B
Hypertonic Isotonic Hypotonic
Active Transport
• Requires the cell to use energy
• Actively moves molecules to where they are
needed
• Molecules move against the concentration
gradient - from an area of low concentration
to an area of high concentration
• (Low High)
• Three Types:
Types of Active Transport
1. Protein Pumps -
transport proteins that
require energy to do work
• Example: Sodium /
Potassium Pumps are
important in nerve
responses.
Sodium Potassium
Pumps (Active
Transport using
proteins)
Protein changes
shape to move
molecules: this
requires energy!
Types of Active Transport
• 2. Endocytosis: taking bulky
material into a cell by forming a vesicle
• Uses energy
• Cell membrane in-folds around food particle
• “cell eating”
• forms food vacuole & digests food
• This is how white blood cells eat bacteria!
Types of Active Transport
3. Exocytosis: Forces material out of cell in bulk
• Membrane surrounding the material fuses with cell membrane
• Cell changes shape – requires energy
• Ex: Hormones or wastes released from cell
Endocytosis &
Exocytosis
animations