Cell Boundaries The Cell Membrane

The Cell Membrane Thin, flexible barrier Regulates what enters and leaves Protects and supports

aka: Phospholipid Bilayer. Consists of: hydrophilic head (water liking) and a hydrophobic tail. (water avoiding)

Phospholipid Bilayer: Fluid Mosaic Model Also has Proteins – doorways Carbohydrates – name tags Cholesterol – keeps membrane flexible Therefore referred to as a “fluid mosaic” of different molecules.

Assignment Draw and label Figure 6 from page 188. Black and white okay. Do this in your journal. You will see a similar diagram on your test. Complete the Cells Practice worksheet

Other Components and Functions Proteins and carbohydrate chains Protein channels/pores Protein “pumps” or “carrier proteins” Cholesterol Act like “chemical id cards” so same cells can ID each other. Allow some molecules to pass in or out without using energy. Use energy to admit or send charged or larger molecules across the membrane. Provides structure.

The Function of the Plasma Membrane Cell Boundaries The Function of the Plasma Membrane

The Cell Membrane Cells want nutrients Cells get rid of wastes Two ways: Passive Transport – No Cell Energy (ATP) needed Active Transport – Cell Energy (ATP) required

Passive Transport - Diffusion Molecules move from high to low concentration (with the “concentration gradient”) until “dynamic equilibrium” is reached. Simple diffusion – small particles move between phospholipids of membrane Facilitated diffusion – large particles move through transport proteins

Passive Transport - Diffusion

Passive Transport – Facilitated Diffusion

Passive Transport - Osmosis The diffusion of water molecules through a cell membrane. Concentration gradient depends on amount of dissolved particles (like salt) inside and outside the cell.

Isotonic Solution Concentration of a dissolved substance (solute) is the same inside and outside the cell. Isotonic = Dynamic equilibrium. Cell stays same size.

Isotonic Solution

Hypotonic Solution Concentration of the solute is low outside the cell and higher inside the cell. Water moves INTO the cell. Cell gets BIG like the O in hypOtonic

Hypotonic Solution

Hypertonic Solution Concentration of the solute is higher outside the cell and lower inside the cell. Water Exits the cell. Think of the “E” in hypErtonic Cell shrinks.

Hypertonic Solution

Assignment Draw and Label Figure 23, 24 and 25 on page 204-205. Complete the Osmosis worksheet.