 Homeostasis means maintaining a balance internally despite what is going on externally.  Organisms must adjust to changes in the environment in order to survive or they could die!

 For example, if it is below freezing outside, you must put on a heavy coat, gloves, double socks, a warm hat, ear muffs, and lots and lots of layers to maintain a healthy INTERNAL body temperature despite the EXTERNAL temperature

 What structure maintains homeostasis in our cells?  How does it maintain homeostasis?  How? The Cell Membrane By controlling the passage of molecules, such as water, salts, food particles, etc in and out of the cell. (it regulates what enters and leaves) Through passive transport, active transport and cell to cell communication!

The Cell Membrane is:  A phospholipid bilayer  Two layers made of proteins and lipids Phospholipid Structure:  Polar Head (hydrophilic—”water loving”)  Nonpolar Tails—(hydrophobic—”water fearing”) Draw:  Polar Head (hydrophillic) Nonpolar Tails (hydrophobic)

 Bilayer arrangement  Draw:

 The proteins embedded in the cell membrane help it to function properly  3 Types of Membrane Proteins › Transport—helps molecules enter or leave the cell › Marker—identify the cell › Receptor—allow cells to communicate

Transport Proteins  Function as “gates/passageway”  Allow sugars, salts, etc to cross the membrane.  Special channel proteins: › Gated ion channels—gates that open/close › Carrier proteins—change shape to allow specific molecule to pass › Aquaporins-allow water to diffuse through (called osmosis) Channel Protein Carrier Protein Transport Protein

Marker Proteins  Cell’s “Name Tag”  Protein sticks out of phospholipid layer  Often has carbohydrates attached to outside end  Functions in cell identification to identify the cell to other cells and molecules  Important in › immunity—so various white blood cells in your body do not mistake your cells for foreign cells - blood typing – so you can’t receive just any ol’ type of blood Marker Protein

Receptor Proteins  Function as “messenger/receiver”  Receive information from the environment (extracellular fluid, blood, interstitial fluid) and transmit that info to the inside of the cell  Protein has specific shape/charge to only allow certain molecules (like hormones) to bond  Triggers a response in cell textbook/chapter3/cms2.htm Receptor Protein

 Proteins are embedded/float -ing in the lipid bilayer.

The Cell Membrane is:  Selectively permeable/semipermeable  permeable means to let objects travel through  so if it is selectively or semi permeable it only allows SOME things through and not others

 This represents a selectively permeable membrane.  It allows (selects) certain things to pass through it.  Is the membrane permeable to ?

 Molecules pass through the cell membrane through: › Passive Transport  Diffusion  Facilitated Diffusion  Osmosis › Active Transport  Vesicles  Pumps

 Molecule- the smallest unit of a compound/substance › Cannot be seen with the naked eye › 1 drop of water has 16,700,000,000,000,000,000,000 molecules of H 2 0 › 1 grain of salt has 120,000,000,000,000,000 molecules of salt

 Concentration Gradient- an area of high concentration next to an area of low concentration Low Concentration of Molecules High Concentration of Molecules

 Equilibrium is when there is an EQUAL amount of molecules on each side of the membrane  There is no net movement meaning, there is continuous movement of molecules back and forth through the membrane.

 Passive Transport is when molecules move from an area of HIGH concentration to an area of LOW concentration until equilibrium is reached.  Requires NO ENERGY!  Examples: › Diffusion › Osmosis › Facilitated Diffusion

 Diffusion- the process by which molecules (“stuff”) spread from areas of high concentration, to areas of low concentration  Molecules are said to go “Down” or “with” the concentration gradient.  Requires no energy

Where is the greatest concentration of cows? Where is the least concentration of cows? What will happen when the gate is opened?

This process is called… diffusion

 Facilitated Diffusion › What does facilitate mean? › When substances move from high to low concentration (down the concentration gradient) using channel/carrier proteins located in membrane › Does not require energy

Click, hold, and drag slider to move forward, bckword, or slow down

 A special type of diffusion is called osmosis  Osmosis- the process by which WATER molecules move from an area with a high concentration of water to an area of low concentration of water. › OR the “diffusion of water”  Requires no energy

 In Osmosis water will move in where there is a low concentration of SOLVENT, and a high concentration of SOLUTE › A solute = “stuff” (salt, glucose, food particles) › A solvent = “water”

 There are three ways water can move in a solution: › Hypotonic- water moves INTO a cell and the cell swells (gets bigger) › Hypertonic – water moves OUT of a cell and the cell shrinks (gets smaller) › Isotonic- water moves into AND out of a cell at an equal rate (remember- molecules are constantly moving)

 Hypotonic- › Water moves into the cell (and could burst) › There is more solvent/less solute on the outside of the cell than the inside › So the solvent (water) moves to an area of low solvent (water) concentration

 Hypertonic- › Water moves out of the cell (and will shrink) › There is less solvent/more solute on the outside of the cell than the outside › So the solvent (water) moves to an area of low solvent (water) concentration

 Isotonic- water moves into and out of the cell at equal rates and stays the same size  So the concentration of solvent and solute on the inside of the cell is equal to the concentration of solvent and solute on the outside of the cell

 Draw arrows to show the flow of water  Label at the top if the solution is isotonic, hypotonic or hypertonic

selectively permeable membrane Where is the greatest concentration of solvent? Outside of the bag What type of solution is this? Hypotonic Which way does the water move? Into the Bag

10% salt 90% water Where is the greatest concentration of solvent? In the bag selectively permeable membrane Which way does the water move? Out of the bag What type of solution is this? Hypertonic

What happens to the bag? selectively permeable membrane 90 % solvent 10% salt

What happens to the bag? selectively permeable membrane 90 % solvent 10% salt

What happens to the bag? selectively permeable membrane 90 % solvent 10% salt

What happens to the bag? The bag shrinks. selectively permeable membrane 90 % solvent 10% salt

 Passive transport: › requires no energy › moves from high concentrations to low concentrations › Moves down the concentration gradient › Includes diffusion, facilitated diffusion and osmosis

 When molecules must move from a low concentration to a high concentration they must use active transport › Cells must transport certain amino acids, sugars, etc. into their cytoplasm from the surrounding fluid. › Some of these substances, however, are already in higher concentrations inside versus outside.  This requires energy!

 Opposite of Passive Transport  Molecules go against the concentration gradient  Energy is provided by the ATP made in the mitochondria  Active transport can involve pumps or vesicles  Requires energy

 Pumps allow molecules to travel against their concentration gradient  For example, the sodium/potassium pump actively transports sodium molecules and potassium molecules through the cell membrane  Requires energy

 Na + pumped out of a cell  K + pumped into a cell  Important because it prevents cells from bursting by lowering the sodium inside causing less water to enter through osmosis.  Requires energy

Sodium Potassium Pump

Proton (H+) pump – forces protons out of a membrane enclosed space (organelle or cell), often to create a proton gradient down which the protons can flow back in Why would the cell “waste” energy on a proton pump? *Because the cell needs isolated areas of the cell with different pH for particular functions; ex) lysosomes – have proton pumps to maintain a pH=5 *Because the cell only uses one ATP to pump a proton out, and that proton can be used in co-transport Co-transport – process cells use to bring large molecules, such as sugars, into a cell with a minimum amount of energy used; usually a proton and a sugar enter a double tunneled protein at the same time; the tunnel only “works” when both molecules are present

 Vesicles can transport molecules across the cell membrane through: › Endocytosis- moving INTO the cell › Exocytosis- moving OUT of the cell  Requires energy

Pinocytosis (drinking)Phagocytosis (eating)

 Exocytosis can help get rid of wastes or secrete products like hormones or insulin  Requires energy

 Opposite of Passive Transport  Molecules go against the concentration gradient  Energy is provided by the ATP made in the mitochondria  Active transport can involve pumps or vesicles  Requires energy