Homeostasis and Cell Transport

Section 1 Vocabulary Pretest Passive Transport Diffusion Concentration gradient Equilibrium Osmosis Hypotonic Hypertonic Isotonic Contractile vacuole Turgor pressure Plasmolysis Cytolysis Facilitated diffusion Carrier protein Ion channel A.Movement of water from high to low concentration B.Movement of molecules from high to low conc. C.Organelles that remove water from cells D.Pressure exerted by water molecules on cell walls E.Proteins that help move molecules through cells F.State where molecules are evenly spaced G.Difference in the concentration of molecules over a distance H.Bursting of a cell I.Shrinking of a cell J.Assisted diffusion of molecules K.Proteins that move ions through a membrane L.Solution with a low concentration of solute outside a cell M.Solution with a high concentration of solute outside a cell N.Solution with an equal concentration of solute inside and outside a cell O. Moving substances without using energy

Answer Key Passive TransportO DiffusionB Concentration gradientG EquilibriumF OsmosisA HypotonicL HypertonicM IsotonicN Contractile vacuoleC Turgor pressureD PlasmolysisI CytolysisH Facilitated diffusionJ Carrier proteinE Ion channelK

Types of Transport Cells move molecules using different types of passive and active transport These differ from each other by whether or not cells must use energy. Passive= no energy Active = use energy

Passive Transport Passive transport —movement of substances through a membrane that requires NO ENERGY Types: Diffusion —movement of molecules from high to low concentration Osmosis —movement of WATER from high to low concentration Facilitated Diffusion —assisted diffusion of large or insoluble molecules through a cell membrane. Ion Channel Diffusion —movement of ions from high to low concentration.

Diffusion Simplest type of passive transport Moves molecules from high to low concentration They have kinetic energy and are in constant motion. They will spread out simply because they “bump” into each other. They move away from areas where they are too crowded This is called moving down a “concentration gradient” Concentration gradient is the difference in concentration of molecules across a distance Diffusion can happen in a gas, liquid or solid It can happen in a living or nonliving system It is how most molecules pass into and out of cell membranes. It continues until equilibrium is reached Equilibrium —the concentration of molecules is the same throughout the space they occupy

How Diffusion Works Animation Note: Even at equilibrium the random movement of molecules continues but we no longer see a net movement of molecules in one direction

Cell membranes are semi-permeable: some molecules can pass through and some cannot. Depends on size and chemical nature of the molecule Passing unassisted through the membrane is called simple diffusion Example: CO2 and O2 dissolve in lipids and can pass directly through the phospholipid bilayer Example: Molecules like NH3 and some hormones that can’t dissolve in lipids but are small enough can pass through the Channel Protein Pores in the membrane

Osmosis Osmosis is the diffusion of WATER from high to low concentration. Direction of osmosis (water movement) depends on the relative concentration of solutes inside and outside the cell Review: Solute —substance dissolved in water (Ex: sugar, salt) Solvent —water Pay attention!! This gets confusing!!

Hypotonic Solution —a solution outside the cell that has a lower concentration of solute molecules than the concentration inside the cell. Ex: (less salt outside the cell) This means that there is a higher concentration of solvent outside the cell. Ex (more water outside the cell) So water will move into the cell by osmosis. “Hypo” means less

Hypertonic Solution —a solution outside the cell that has a higher concentration of solute molecules than the concentration inside the cell. Ex: (more salt outside the cell). This means that there is a higher concentration of solvent inside the cell. Ex: (more water inside the cell) So water will move out of the cell by osmosis. “Hyper” means more

Isotonic Solution — concentrations of solute are equal both inside and outside the cell. Water will move in both directions in even amounts.

Some cells control osmosis to some degree Three methods: Contractile Vacuole —structures found in certain cells (usually cells of freshwater organisms that constantly have water moving in) that pump excess water out. Ex. Paramecium Solute Pumps —pump out solutes so that water is less likely to move in. Cell Walls —support the cell so when water moves in the cell does not burst. Creates “turgor pressure” which keeps plants upright. “Plasmolysis” is the shrinking of the cells cytoplasm creating a loss of turgor pressure. Result: plant wilts

Contractile Vacuole

Solute Pump

m/lect09.htm Turgor Pressure and Plasmolysis

Cytolysis —bursting of a cell due to osmosis. Identify the pictures as a cell in an isotonic solution, hypertonic solution and hypotonic solution IsotonicHypotonicHypertonic

Facilitated Diffusion Assisted diffusion of large or insoluble molecules through a cell membrane. Carrier Proteins help the molecules to move from high to low concentration. Glucose is transported to cells in this way. BK9847/

Ion Channel Diffusion Several ions are vital to cells but cannot pass through the cell membrane because they are not soluble in lipids. They are: Sodium (Na + ) Potassium (K + ) Calcium (Ca 2+ ) Chlorine (Cl - ) They require specific ion channels to pass through membranes

Many ion channels have gates that close or open in response to three stimuli: 1. stretching of cell membrane 2. electrical signals 3. chemical signals

Section 2 Vocabulary Pretest Active Transport Sodium-potassium Pump Endocytosis Vesicle Pinocytosis Phagocytosis Phagocyte Exocytosis A.Releasing large molecules from a cell B.The movement of molecules from low to high concentration using energy C.Taking large molecules into a cell D.Organelles that form from the cell membrane and transports molecules within the cell E.Carrier protein the transports sodium ions out of a cell and potassium ions into a cell F.Type of endocytosis that takes in liquids G.Type of endocytosis that takes in solids H.White blood cell

Answer Key Active TransportB Sodium-potassium PumpE EndocytosisC VesicleD PinocytosisF PhagocytosisG PhagocyteH ExocytosisA

Active Transport Active Transport —movement of substances through a cell membrane that REQUIRES ENERGY. Molecules move from low to high concentration ( “up” their concentration gradient). The Carrier Proteins involved require energy from ATP and are called Cell Membrane Pumps. Example: Sodium-potassium pump

Importance of the Sodium-potassium pump The sodium-potassium pump is important in animals to maintain the normal function of many cells including nerve cells. The exchange of three sodium ions for two potassium ions creates an electrical gradient. The outside of the cell becomes positively charged and the inside becomes negatively charged. This helps nerve cells to conduct electrical impulses

Endocytosis Movement of VERY LARGE PARTICLES into a cell. The cell membrane pinches off to trap the particle inside a vesicle which can then transport the particle throughout the cell.

Two types of endocytosis: Phagocytosis—movement of large particles or whole cells Pinocytosis—movement of fluids

Exocytosis Movement of VERY LARGE PARTICLES out of a cell. Vesicles bring particles to the cell membrane to be released.