Focus Concept: Stability and Homeostasis 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