PLASMA MEMBRANE A Plasma Membrane function 1 Acts

PLASMA MEMBRANE • A. Plasma Membrane (function): • 1. Acts as a boundary between the Cell and its environment • 2. Helps the cell maintain homeostasis • (regulation of its internal environment) • 3. Is selective because it allows only certain substances into and out of a cell

B. Plasma Membrane (structure) • • • 1. Composed of a Phospholipid Bilayer. 2. Lipids Have: A. Glycerol backbone B. Two Fatty Acids C. Phosphate group

• 3. The Fatty Acid tails are nonpolar • A. Do not attract polar molecules • B. Are hydrophobic (water-fearing)

• • 4. The head is polar (phosphate group) A. Attracts polar molecules B. is hydrophilic (water-loving) C. Interacts with water and other polar molecules

• 5. The two phospholipid layers form a sandwich • 6. The model is called Fluid Mosaic because it has a Flexible Membrane with Proteins embedded. Proteins Protein channel Carbohydrate chains Lipid bilayer

• 7. Other components of the Plasma Membrane include: • A. Cholesterol • 1. Stabilizes Phospholipids • 2. Prevents fatty acid from sticking together

• B. Transport Proteins • 1. allows needed substances or waste to move through the plasma membrane • 2. makes the cell semi-permeable Proteins Protein channel Carbohydrate chains Lipid bilayer

• • • C. Other proteins help in cellular 1. support 2. flexibility 3. identification 4. as enzyme receptors 5. cell to cell adhesion

Draw the Fluid Mosaic model of the cell membrane: Carbohydrate chains Protein channel Lipid bilayer

Write a description of the fluid mosaic model using the following terms: • Plasma membrane, phospholipid bilayer, polar, nonpolar, and proteins

DEMO • Diffusion Across A Membrane (Starch) • Are cell membranes semi-permeable (selectively permeable)?

CELL (PLASMA) MEMBRANE • Regulates what enters and leaves; provides protection and support. • It is a semi-permeable (selective) membrane Proteins Protein channel Carbohydrate chains Lipid bilayer

• Concentration-is the mass of solute in a given volume of solution (and determines whether things enter or leave the cell).

Diffusion • Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration • Affected by Concentration, Temperature, and Pressure

Osmosis • Diffusion of water across a membrane Controlled by a concentration gradient (Unequal distribution of molecules or SOLUTE) Note: Movement of water is due to the concentration solute in the environment

• Solute concentration in the environment is lower than in the cell • Water moves into the cell • As water diffuses into the cell, pressure –called turgor pressure – increases; the cell swells • Cytolysis occurs when a cell takes in so much water that it burst

Solute concentration in the environment is the same as that in the cell Equal amounts of water will move into and out of the cell Cell volume is constant

• Solute concentration in the environment is higher than that in the cell • The cell will shrink • Plasmolysis – occurs when water leaves the cell, turgor pressure is lost and the cell wilts

Diffusion & Osmosis • Stops when equilibrium is made. Movement still occurs, but no change in concentration occurs.

Example of Osmosis in Animal Cells Hypotonic Hypertonic

Example of Osmosis in Plant Cells Hypotonic Hypertonic

Passive Transport • Water, lipids, lipid soluble substances pass through cell membranes by diffusion (high to low) • The cell uses no energy & channel proteins (transport proteins)

Facilitated Diffusion – a form of Passive Diffusion • Movement of molecules and ions across the membrane using carrier proteins (transport proteins) • Common method of moving sugars, amino acids, etc. • Is driven by a concentration gradient

Active Transport • Movement of materials through a membrane against a concentration gradient • Requires energy from the cell • Particle movement may occur into and out of the cell • Uses carrier proteins

Endocytosis • Type of Active Transport • Cell surrounds and takes in material from its environment • Material is engulfed and enclosed by a portion of plasma membrane (becomes a vacuole) • Requires cellular respiration (energy) • EX. Pinocytosis (small) & Phagocytosis (large)

Exocytosis • Type of active transport • Used by cells to expel or secrete materials • Requires cellular respiration or energy