2A4. Homeostasis and Transport Describe how the structure of the plasma membrane allows it to function as a regulatory structure and/or protective barrier for a cell.Compare the mechanisms that transport materials across the plasma membrane.Explain how organisms maintain homeostasis.Describe how membrane-bound organelles facilitate the transport of materials within a cell.
3A4. Vocabularyplasma membrane lipid bilayer phospholipid impermeable selectively permeable protein channel protein pump osmosis diffusion facilitated diffusion active transport passive transport endocytosis exocytosis isotonic equilibrium hypertonic concentration gradient hypotonic homeostasis
4Cell Membrane Structure and function A phospholipid bilayerCell membranes are composed of phospholipidsPhospholipids are arranged in two layers (bilayer)Each phospholipid has a “head” and two “tails”The head loves water (hydrophilic)The tails hate water (hydrophobicThe lipid bilayer is flexible but strong
5Cell Membrane Structure and Function DRAW THIS in your NOTES!!
6Cell Membrane Structure and Function Fluid Mosaic ModelThe cell membrane acts as a fluid…It is not rigidProteins and phospholipids can move aroundThe cell membrane is a mosaic…Many different parts make up the cell membrane
7Cell Membrane Structure and Function Functions of the Cell MembraneBarrier between the cytoplasm and the environmentProtects and supports the cellControls everything that enters and leaves the cell
8Cell Membrane Structure and Function PermeabilityMembranes are selectively permeableSome things can cross the membrane (permeable)Gases, water, small particlesSome things can cross the membrane with the help of a protein channel or pumpIons, proteins, large particlesSome things can’t cross the membrane (impermeable)
9Let’s Build a Model of a cell membrane! Cotton swabs represent phospholipidsOther components are embedded within the phospholipid bilayerCan you move the components back and forth?
10Can you do it?Give as many names for the boundary of the cell as you can…
11Mechanisms of Passive Transport Passive Transport Definedrequires NO energyDepends on a concentration gradient (difference)Concentration = relative amount of substanceSUBSTANCE moves from HIGH concentration (of substance) to LOW concentration (of substance)Some materials can pass freely, other materials need a protein channel
12Mechanisms of Passive Transport Passive Transport is like…Create an analogy…The hill is like the concentration gradientThe ball is like a molecule moving down its gradientIn a cell this gradient has to do with concentration of materials on either side of the membraneA ball rolling down a hill
13Mechanisms of Passive Transport 1. Diffusion (a.k.a. simple diffusion)Passive transportDepends on a concentration gradientConcentration = relative amount of substanceGradient = differenceMOVEMENT from HIGH concentration to LOW concentrationDown the concentration gradient
15Mechanisms of Passive Transport 2. Facilitated DiffusionPassive – requires NO energyDepends on a concentration gradient (difference)Concentration = relative amount of waterMOVEMENT from HIGH concentration to LOW concentrationjust like simple diffusion EXCEPT needs a protein channel
17Mechanisms of Passive Transport 3. OsmosisDiffusion of waterWATER moves from HIGH concentration (of water) to LOW concentration (of water)Aquaporins = protein channels for water to passPlays a role in maintaining homeostasis (water balance)
18Which way will the water molecules move? OsmosisWhich way will the water molecules move?Why wouldn’t the green or purple molecules move?
19Mechanisms of Active Transport DefinedRequires energyMaterial flows AGAINST the concentration gradientFrom LOW concentration to HIGH concentrationRequires protein pumps (need energy to work)
201. Protein Pumps Movement within a cell Use ATP energy to move or “pump” material into an area that already has a high concentrationIt’s like pumping air into a basketball
222. Bulk Transport Movement within a cell Used to transport very large molecules or foodEndocytosis = bringing materials into the cellExocytosis = taking materials out of the cellCell membrane/vesicles play a role
25Defined Homeostasis Maintaining stability in the cell or body Variables within the body can fluctuateTemperature, pH, water balanceImportant to maintain homeostasis near set pointCell membrane aids in maintaining homeostasis
26Osmosis and water balance HomeostasisOsmosis and water balanceDiffusion of waterPassive (no energy required)Water will move across the membrane down its concentration gradientCell membrane regulates the amount of water inside a cell
27ISOTONIC Conditions Homeostasis Amount of water inside = amount of water outsideWater moves back and forth across the membrane equally in both directionsEquilibrium = equal concentrations of water on both sides of the membrane
28HYPERTONIC Conditions HomeostasisHYPERTONIC ConditionsAmount of solute surrounding cell is high (high solute = low water)Water moves out of the cell to balance concentrations of water on both sides of membraneCell shrinks (dehydrates)EX: saltwater
29Hypotonic conditions Homeostasis Amount of solute surrounding cell is low (low solute = high water)Water moves INTO the cell to balance concentrations of water on both sides of membraneCell swells (animal cells could burst)EX: pure water
31Why would plant cells be better off than animal cells Why would plant cells be better off than animal cells? What would happen to the cells of a freshwater fish if it was put into a saltwater tank?
32Cell Transport Review Divide your poster into six sections In each section, diagram one of the following modes of transportSimple diffusionFacilitated diffusionOsmosisActive transport via protein pumpsExocytosisendocytosis
33Keystone QuestionsCarbon dioxide and oxygen are molecules that can move freely across a plasma membrane. What determines the direction that carbon dioxide and oxygen move?Orientation of cholesterol in the plasma membraneConcentration gradient across the plasma membraneConfiguration of phospholipids in the plasma membraneLocation of receptors on the surface of the plasma membrane
34Keystone QuestionsA sodium-potassium pump within a cell membrane requires energy to move sodium and potassium ions out of a cell. The movement of glucose into or out of a cell does not require energy. Which statement best describes the movement of these materials across a ac cell membrane?Sodium and potassium ions move by active transport, and glucose moves by osmosisSodium and potassium ions move by active transport and glucose moves by facilitated diffusion.Sodium and potassium ions move by facilitated diffusion and glucose moves by osmosisSodium and potassium ions move by facilitated diffusion and glucose moves by active transport
35Keystone QuestionsWhich example is an activity that a fish most uses to maintain homeostasis within its body?Using camouflage to avoid predatorsFeeding at night to regulate body temperatureMoving to deeper water to regulate metabolic wastesExchanging gases through its gills to regulate oxygen levels.
36Keystone Questions 4. Diffusion occurs because Molecules are attracted to one anotherMolecules constantly move and collide with one anotherCellular energy forces molecules to collide with one anotherCellular energy pumps molecules across the cell membrane
37Keystone QuestionsDuring diffusion, when the concentration of molecules on both sides of the membrane are equal, molecules willMove across the membrane to the outside of the cellStop moving across the membraneContinue to move across the membrane in both directionsMove across the membrane to the inside of the cell