A.K.A Plasma Membrane A.K.A lipid bilayer The Cell Membrane A.K.A Plasma Membrane A.K.A lipid bilayer

What is the Cell Membrane? Outer boundary of the cell Separates the cell from its surroundings

What does the cell membrane do? Regulates what enters and leaves the cell Provides protection Provides support

Cell Membrane Structure Composed of a double layer of phospholipids. What is a phospholipid? Made of phosphate head Fatty tail

Cell Membrane Structure Lipid Bilayer: double layer of lipids Hydrophilic Heads: like water so they point outwards towards the surrounding environment Hydrophobic Tails: don’t like water, they point inwards between the layers away from the water Result = strong, flexible barrier

How do they organize Line up with phosphate heads out towards water because they are hydrophilic. Hydrophilic = water loving Fatty tails toward the middle because they are hydrophobic Hydrophobic = water fearing

Imbedded into the fluid-like bilayer of lipids are proteins This is called the "fluid-mosaic model."

Cell Membrane Structure Proteins: within the lipid bilayer, help in transport of materials across membrane, receive messages from other parts of the cell Carbohydrate chains: ID cards, each cell has a specific chain attached to the membrane. If it is a foreign cell, antibodies will read the carb. chain and destroy it

Moving substances into the cell Osmosis and Diffusion Moving substances into the cell

Solute and Solvent Solute: a substance dissolved in a solvent to make a solution Ex. Salt, Sugar, (usually solids) etc… Solvent: a substance that a solute is dissolved in. Ex. Water, alcohol, (usually liquid) Water will move in the direction where there is a high concentration of solute (salt) and hence a lower concentration of solvent (water).

SALT SUCKS A simple rule to remember is: Salt is a solute, when it is concentrated inside or outside the cell, it will draw the water in its direction. This is also why you get thirsty after eating something salty

Diffusion Molecules move from an area of greater concentration to an area of lesser concentration Concentration: how much stuff in a given area

Simple Diffusion Animation Passive Transport: Simple Diffusion Animation Diffusion: random movement of particles from an area of high concentration to an area of low concentration. (High to Low) Diffusion continues until all molecules are evenly spaced (equilibrium is reached)- Equilibrium- equal concentration on both sides of membrane http://bio.winona.edu/berg/Free.htm

Selectively Permeable only some substances can pass through the membrane without using energy Substances like glucose cannot pass through because they are too big. Substances like water pass through easily because they are small. http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flash/Osmosis_Animation.htm

Passive Transport: Osmosis animation Osmosis: diffusion of water through a selectively permeable membrane Water moves from high to low concentrations Water moves freely through pores. Solute (green) to large to move across.

Isotonic Solution Iso= same Isotonic: The concentration of solutes in the solution is equal to the concentration of solutes inside the cell. Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium)

Examples of Isotonic Solutions Normal saline solution (0.9% NaCl) is considered isotonic with blood. Also used for intravenous infusion, rinsing contact lenses, and nasal irrigation

Hypotonic Solution Hypo= less Hypotonic: The solution has a lower concentration of solutes and a higher concentration of water than inside the cell. (Low solute; High water) Result: Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)!

Hypotonic Examples In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid, the cell wall keeps the plant from bursting In animal cells, the cell may be in danger of bursting (lysis), Organelles called CONTRACTILE VACUOLES will pump water out of the cell to prevent this.

Hypertonic Solution shrinks Hyper= more Hypertonic: The solution has a higher concentration of solutes and a lower concentration of water than inside the cell. (High solute; Low water) shrinks Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)!

Examples of Hypertonic Solutions In plant and animal cells, the vacuole loses water and the cells shrink, causing wilting. In both cases, the cell may die.

Don’t Drink the Water This is why it is dangerous to drink sea water - its a myth that drinking sea water will cause you to go insane, but people marooned at sea will speed up dehydration (and death) by drinking sea water.

Evil People This is also why "salting fields" was a common tactic during war, it would kill the crops in the field, thus causing food shortages.

B C A What type of solution are these cells in? Hypertonic Isotonic Hypotonic

How Organisms Deal with Osmotic Pressure Paramecium (protist) removing excess water video Bacteria and plants have cell walls that prevent them from over-expanding. In plants the pressure exerted on the cell wall is called tugor pressure. A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from over-expanding. Salt water fish pump salt out of their specialized gills so they do not dehydrate. Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.

Types of Transportation in the Cell Not Planes, Trains, or Automobiles

Passive Transport (HighLow) cell uses no energy molecules move randomly Molecules spread out from an area of high concentration to an area of low concentration. (HighLow) Three types:

3 Types of Passive Transport Osmosis – diffusion of water Diffusion Facilitative Diffusion – diffusion with the help of transport proteins

Facilitated Diffusion Proteins in the cell membrane carry larger, impermeable molecules across the cell membrane (no energy used) From greater concentration to lesser concentration Ex. proteins in red blood cells bring glucose across the cell membrane

Active Transport (Low  High) cell uses energy actively moves molecules to where they are needed Movement from an area of low concentration to an area of high concentration (Low  High) Three Types:

Types of Active Transport Sodium Potassium Pumps (Active Transport using proteins) 1. Protein Pumps -transport proteins that require energy to do work Example: Sodium / Potassium Pumps are important in nerve responses. Protein changes shape to move molecules: this requires energy!

Types of Active Transport 2. Endocytosis: taking bulky material into a cell Uses energy Cell membrane in-folds around food particle “cell eating” forms food vacuole & digests food This is how white blood cells eat bacteria!

Types of Active Transport 3. Exocytosis: Forces material out of cell in bulk membrane surrounding the material fuses with cell membrane Cell changes shape – requires energy EX: Hormones or wastes released from cell Endocytosis & Exocytosis animations