Passive Transport
Focus Concept:
Stability and Homeostasis
Objectives
At the conclusion of today’s lesson students will be
able to…
• Distinguish between osmosis and diffusion.
• Identify the four main types of passive transport
and the factors that affect the rate of diffusion.
• Explain how the process of diffusion, active
transport and passive transport occur and why
they are important to cells.
• Predict the effects of a hypertonic, hypotonic and
isotonic solution on a cell.
• Investigate and observe the process of diffusion.
• Explain the importance of homeostasis within the
cell.
Passive Transport
• The movement of molecules across the
cell membrane without an input of energy
from the cell.
– Examples
•
•
•
•
Diffusion
Osmosis
Facilitated Diffusion
Diffusion through Ion Channels
Concentration Gradient
The difference in the
concentration of molecules
across a space.
Higher
Concentration
Lower
Concentration
Without other influences present, diffusion will cause
the concentration of molecules to become the same
throughout reaching a state of EQUILIBRIUM.
What factors affect the
rate of diffusion?
•
•
•
•
•
Temperature
Stirring
Particle size
Type of solute
Type of solvent
Osmosis vs. Diffusion
Osmosis
• Movement of water
molecules from areas of
high concentration to
areas of lower
concentration.
• Osmotic direction is
determined by:
– Hypertonic Solutions
– Hypotonic Solutions
– Isotonic Solutions
Diffusion
• Movement of molecules
from an area of higher
concentration to an area
of lower concentration.
• Diffusion driven by the
kinetic energy in
molecules moving down
their concentration
gradient until the reach
equilibrium.
Hypertonic-Isotonic-Hypotonic
Facilitated Diffusion
• The movement of substances across a
membrane assisted by specific proteins in
the membrane known as carrier proteins.
• Three steps in facilitated diffusion:
– Carrier protein binds to molecule on one side
of the membrane
– Carrier protein changes shape, to protect
molecule from the interior of the membrane.
– The molecule is released on the other side of
the membrane.
Diffusion through Ion Channels
• Movement of important ions through the cell membrane
using special proteins called ion channels.
• Which ions move across the membrane this way?
–
–
–
–
Sodium (Na+)
Potassium (K+)
Calcium (Ca2+)
Chloride (Cl-)
• Each channel is specific for each ion. Some ion channels
are always open, others have “gates”.
– Gates can open or close by three stimuli:
• Stretching of the cell membrane
• Electrical signals
• Chemicals in the cytosol or external environment.
Endocytosis
& Exocytosis
(Active Transport)
IN
OUT