1. Focus Concept: Stability and Homeostasis
Passive Transport
Focus Concept:
Stability and Homeostasis

2. 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.

3. 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

4. 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.

5. What factors affect the rate of diffusion?
Temperature
Stirring
Particle size
Type of solute
Type of solvent

6. 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.

7. Hypertonic-Isotonic-Hypotonic

8. 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.

9. 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.

10. Endocytosis & Exocytosis (Active Transport)IN
OUT