Slide 1

Cellular Transport

Define HOMEOSTASISMaintaining a relatively constant or stable internal environment, even when external conditions change dramaticallyGive the function of each of the following organellesCell (plasma) membrane a flexible boundary between a cell and its environmentallows nutrients into the cell no matter what the external conditions are.

Give the function of each of the following organellesLysosome Clean up crew break down organelles that have outlived their usefulnessBreak down lipids, carbs, proteins

Golgi Apparatus Modifies, sorts and packages proteins and other materials from the ER for storage in cell or release outside of cell

Homeostasis and Transport IntroHow does the cell membrane maintain homeostasis?Cell membranes help organisms maintain homeostasis by controlling what substances may enter or leave cellsLabel and describe as many parts/features of the cell membrane as you can:

Components of Cell Membrane:

Key Terms Associated with Transport:Concentration Gradient - difference in amount of molecules across spaceDown the concentration gradient:Higher Concentration Lower ConcentrationUp the concentration gradient: Lower Concentration Higher ConcentrationEquilibrium - when the concentration is the same throughout

Concentration Gradient:

Types of Transport:Passive Transport movement of molecules down their concentration gradient without the use of energy

Active Transport- movement of molecules up their concentration gradient with the use of energy

Passive and Active Transport

Passive Transport:Determining FactorsSizeType of MoleculeChemical Nature of membrane

Small, nonpolar, hydrophobic molecules

4 Types of Passive Transport

Diffusion

Osmosis

Facilitated Diffusion

(Diffusion) Ion channels

Diffusion:

Diffusion:Process by which molecules tend to move from an area where they are more concentrated to an area where they are less concentrated (passive)

Osmosis:Diffusion of water through a selectively permeable membrane (passive)(from an area of higher water concentration to an area of lower water concentration)

Osmosis:

Diffusion vs. Osmosis

Solutions Can Be:Isotonic - solute concentration same on each side of membraneNo net change in cell size

Solutions Can Be:Hypotonic - Solution with a solute concentration lower than cellWater will diffuse into cell until equilibriumThe cell swells and may burst

Solutions Can Be:Hypertonic - Solution with a solute concentration higher than the cellWater will diffuse out cell until equilibriumThe cell shrinks

Effects of Osmosis:

Water diffuses from a hypotonic to a hypertonic solutionDealing with Osmosis:Plants (root cells) swell in a hypotonic environmentThe swelling stops when the cell membrane is pressed against the cell wallThe cell wall is strong enough to resist the pressure, called turgor pressure (pressure exerted against the cell wall in a hypotonic environment)

Cytolysis and Plasmolysis:Cytolysis In a hypotonic solution, cells can swell and eventually burstPlasmolysis - In a hypertonic environment, water leaves the cell and the cell shrinks away from the cell wall as turgor pressure is lost

Contractile Vacuole:Unicellular freshwater organisms (Paramecium) live in a hypotonic environment Contractile Vacuole - collects excess water and pumps it out of cell

Review Questions:1. Toward what condition does diffusion eventually lead, in the absence of other influences?2. How is osmosis related to diffusion?3. If the concentration of solute molecules outside a cell is lower than the concentration in the cytoplasm, is the external solution hypotonic, hypertonic, or isotonic to the cytosol?4. Sea water has a higher concentration of solutes than do human body cells. Why might drinking large amounts of sea water be dangerous to humans?Facilitated DiffusionMovement of specific molecules across cell membranes through protein channels (passive)(diffusion of materials across a cell membrane assisted by carrier proteins)

Facilitated DiffusionMove molecules, (that cannot diffuse easily), down their concentration gradient Move into or out of cellExamples: Glucose, Amino Acids, Ions, Polar molecules (water)Assisted by carrier proteins on the membraneSpecific to one type moleculeMore protein=faster diffusionFacilitated Diffusion of Glucose:

Ion ChannelsNa+, K+, Ca2+, Cl-Provide protein channels for ions to diffuse

Specific to Ion

Two typesOpenGatedopen and close in response to specific stimuli

Active Transport:Cells use energy to move up concentration gradientATP supplies energy Carrier proteins act as pump

SODIUM-POTASSIUM PUMP:In animal cells transport Na+ and K+ up the Concentration Gradient3 Na+ moved outside of cell2 K+ moved inside cell

Steps for Transport3 Na+ bind to carrier protein in cytoplasmCarrier protein splits phosphate group from ATPP group binds with carrier proteinshape changesreleases Na+Now can pick up 2 K+ on outsideCarrier protein changes shape releases K+

Exocytosis and Endocytosis:Transport large molecules across membraneTransport a large amount of small moleculesEnergy used

Exocytosis:Exporting large molecules outside of cellProcessPackaged in Golgi ApparatusVesicle transports to cell membraneVesicle fuses to membraneContents releasedVesicle becomes part of membrane

Endocytosis:Cells take in (ingest) substancesProcessDepression in cell membrane folds in enclosing material from outside of the cellPinched off forming a membrane-bound vesicleVesicle fuses with lysosomesFuse with other organelles

3 Types of Endocytosis:PinocytosisCell DrinkingIngestion of tiny dropletsPhagocytosis-Cell EatingEngulfs large, solid molecule or whole cells (like bacteria)Receptor-mediatedSpecificIngestion of specific substances that bind to receptor proteins on specialized areas of cell membrane3 Types of Endocytosis:

Review Questions:1. Explain the difference between passive and active transport.2. What provides the energy that drives the sodium-potassium pump?3. Explain the difference between phagocytosis and pinocytosis.4. During intense exercise, potassium tends to accumulate in the fluid surrounding muscle cells. What membrane protein helps muscle cells counteract this tendency? Explain your answer.