Cell Transport
maintaining homeostasis
Passive Transport
Does NOT require any ATP or
energy
Happens automatically
Channels may be used in cell
membrane
Passive Transport
This type of transport moves from an area of
high concentration to low concentration
Diffusion
Type of passive transport
When molecules move from an area of
higher concentration to an area of lower
concentration until equilibrium is met
What affects the rate of
diffusion?
Concentration of the solution
Temperature of the solution
Pressure also speeds up
particle motion
Concentration
The amount of dissolved solute in a
solution
Molecules will move to an area less
concentrated
Molecules diffuse through the cell
membrane of cells
Concentration gradient
The difference in concentration in a
solution between a cell and its
surroundings
Concentration Gradient
No gradient - even distribution
Concentration to the right
Increase Rate of
Diffusion
Temperature
Molecules move faster
in higher temperatures
Pressure
Increasing pressure
also increases rate of
diffusion
Equilibrium
This occurs when there is no longer a
concentration gradient
Molecules are evenly dispersed but still
continue to move randomly
Cell Membrane
Movement through membrane
Cell membrane is surrounded by water
Phospholipid bilayer
Cell Membrane
Forms by itself in
water
Proteins imbedded
Markers
Receptors
Channels
Diffusion in cells
Small molecules
diffuse in and out of
the cell to reach
equilibrium on both
side of the membrane
Osmosis
Diffusion of water across a biological membrane
From an area of high concentration to low
concentration of WATER
Comparing concentrations
Osmosis in Cells
Cells are
surrounded by
water and filled
with water.
Water can move
freely through the
membrane
Direction of Osmosis
Hypertonic
Outside cell is more concentrated than cell
ex: 20% salt solution
10% salt solution
The solution with 20% salt is hypertonic
compared to the 10% salt solution
Hypotonic
Outside the cell is less concentrated than cell
ex: 10% salt solution
20% salt solution
The solution with 10% salt is hypotonic
compared to the 20% salt solution
Isotonic
Equal concentrations
ex: 10% salt solution
Equilibrium is reached
10% salt solution
Osmotic Pressure
Net movement of water
into cells
Determined by solute
concentration
Osmosis - hypertonic
Higher concentration in solution
Ex: a cell in salt water
If molecules are too large to fit through cell
membrane or protein channels
Water will diffuse OUT of the cell to reach
equilibrium
Cell shrinks
Osmosis - hypotonic
Lower concentration in solution
Ex: a cell in pure water
If molecules are too large to fit through cell
membrane or protein channels
Water will diffuse INTO the cell to reach
equilibrium
Cell swells - may burst!
Osmosis - Isotonic
Equal concentration in solution
If molecules are too large to fit through cell
membrane or protein channels
Water will diffuse IN AND OUT of the cell to
maintain equilibrium
Osmosis in Plant Cells
Turgor Pressure
Pressure on the walls of the plant cells due to
vacuole filling
Increase in turgor pressure is increase in water
to cell
Plasmolysis
When a cell shrinks due to lack of water
Red Onion Cells Isotonic
Red Onion Cells Hypertonic
Red Onion Cells Hypotonic
Facilitated Diffusion
When the cell membrane has protein channels
(carrier proteins) where materials are
transported in or out of cell
NO energy needed for this process
Active Transport
Against concentration gradient
From an area of low concentration to an area of
high concentration
Requires cell energy (ATP) because you’re going
AGAINST concentration gradient
3 types of active
transport
Protein channels embedded in
cell membrane
Gated channels
Need energy to open
Protein changes shape when
energy is used
Sodium/Potassium Pump
Step 1: 3 Na+ ions bind to carrier protein
Step 2: ATP binds to carrier protein and
changes shape allowing Na+ to move out of the
cell
Step 3: 2 K+ ions move into carrier protein
Step 4: ATP binds to carrier protein and
changes shape allowing K+ to move into the cell
Movement in Vesicles
Endocytosis - INTO the cell
Cell membrane is used to create a vesicle around
particles
Phagocytosis
Particle ingestion
Pinocytosis
Liquid ingestion
Movement in Vesicles
Exocytosis - OUT of the cell
Vesicles created in the cell fuse with cell
membrane and release particles/liquids
Known as bulk transport