Homeostasis and Cell Transport Chapter 5 Plasma Membrane Phospholipids : Phosphate head: part polar (like water), Lipid tails: part non-polar (lipid or anti-water) Bilayer semipermeable Membrane Proteins: integral proteins are integrated into the membrane to some degree some, emerge from only one side like cell-surface markers: cell-cell recognition, dock for viruses others, go clear across the bilayer of membrane like receptor or transport proteins. active transport proteins passive transport protein channels for ions or large molecules. still others, lie on only one side of the membrane but are not embedded into it. For example, enzymes Plasma Membrane Passive Transport Crossing cell membrane using NO energy. EXAMPLES: Diffusion Osmosis Facilitated Diffusion Diffusion through ion channels Diffusion Movement of molecules from an area of higher concentration to an area of lower concentration. Concentration gradient: the difference in the concentration of molecules across a distance Diffusion Diffusion is driven entirely by the molecules kinetic energy. Moving down the concentration gradient. Diffusion Equilibrium- the concentration of molecules will be the same throughout Osmosis The process by which water molecules diffuse across a cell membrane from an area of higher concentration to an area of lower concentration Does not require energy Osmosis Hypo- : under Hyper-: over -tonic : solute (I say salty) Iso-: same or equal Review: solute + solvent = solution Net direction depends on relative concentration of solutes on the two sides of the membrane. Directions of Osmosis Hypotonic solution- The solution has lower concentration of solute Directions of Osmosis Hypertonic solution- the solution has a higher concentration Directions of Osmosis Isotonic solution- Concentrations are equal How Cells Deal with Osmosis Contractile vacuoles- pump water out of cells, uses energy, maintain homeostasis How Cells Deal with Osmosis Turgor pressure- pressure that water molecules exert against the cell wall Plasmolysis- loss of turgor pressure, plants wilts Cytolysis- bursting of cells FACILITATED DIFFUSION Process used for molecules that cannot readily diffuse through cell membrane Glucose, sodium ions and chloride ions are just a few examples of molecules and ions that must efficiently cross the plasma membrane but to which the lipid bilayer of the membrane is virtually impermeable. FACILITATED DIFFUSION Channel is SPECIFIC for ion Some are always open Some are gated and open with a stimulus Stimuli examples: (stretch, electrical, chemical) Carrier Proteins Ion Channels What if passive transport wont work? Brain storm the following questions with your table partner. Be prepared to share. Can you think of examples where cells need to get stuff in or out of the cell and passive transport wont work? How do you think cells can get stuff in or out without using passive transport? Active Transport Move materials from an area of lower concentration to an area of higher concentration, or up their concentration gradient Active Transport Crossing cell membrane using energy. Driven by chemical or ATP energy. Always from Low concentration to High (L H) Moving up the concentration gradient. Active Transport Example: Sodium-Potassium Pump (Na + -K + pump) MOVEMENT IN VESICLES Endo: means into Exo: means to exit -cytosis: the cell Endocytosis Gulping food Importing Large packages of lots of small stuff Pinocytosis: fluid sipping Phagocytosis: large particles or whole cells gulping. Exocytosis: Exporting substances OUT OF the cell Used to eject: protein products of the cell waste products toxins All kinds of Cells Only 4 types of Tissues!! Tissue Neurons Neurons are cells that make up nervous tissue. Neurons transmit nerve messages. This image is copyright Dennis Kunkel at Neurons Axon endings (synaptic terminals) Nucleus Axon Dendrites Cell Body Nerve impulses go only one way Nerve Impulse Self propagating wave of electrical disturbance Sodium (Na+) ions racing inward Inside + Outside - Keeps going down the membrane of the axon The myelin sheath helps make it go faster