2 Cell Membrane Controls what enters and leaves the cell Like water, nutrients and wasteThe membrane is Selectively PermeableMembrane selects which molecules can permeate (pass through) into the cell.Like a window screen – allows what you want in and keeps others out.
3 Structure of Plasma Membrane Lipid Bilayer (2 layers of phospholipids)Lipids with phosphate “heads” attachedHead of phospholipid is polarHydrophilic (points outward, likes watery environment)Fatty acids (tails) are nonpolarHydrophobic (points inward, avoids water)
4 Other Membrane Molecules Membrane Proteins - (transport)Allow substances/waste to move in and out of the cell.Creates a tunnel that can be closed or open.Carbohydrates/ Other Proteins-Stick out of cell surface (id card for other cells to see)
6 How stuff gets into the cell 2 ways cell gets nutrients it needs and gets rid of wastePassive TransportRequires no energyActive TransportRequires an input of energy
7 Passive Transport Occurs due to concentration gradient Molecules naturally move from areas of higher concentration to lower concentration (no energy required)Diffusion – natural movement of moleculesFacilitated Diffusion – through protein channelsOsmosis – diffusion of water molecules
8 DiffusionIn nature, molecules ALWAYS move from areas of higher concentration to areas of lower concentration, as is shown in this picture.They move to reach equilibriumThis also happens across the cell membrane!These odor molecules are diffusing from the bottle (area of high concentration) to the surrounding air (lower concentration)
9 Facilitated Diffusion Diffusion of molecules through protein channels in the cell membraneUsed for substances that the cell needs but cannot pass through the membraneLarge moleculesCharged (ions)
10 Osmosis The diffusion of water molecules is called osmosis Just like diffusionWater molecules move from areas of higher conc. to areas of lower water conc.They will move until there are equal concentrations of water (and solute) molecules everywhereCalled equilibriumMolecules still diffuse, but at equal rates
11 Osmosis The movement of water molecules across a membrane Water moves from areas of high water conc. to areas of lower water conc.This is how cells maintain a stable internal environmentHomeostasis – reacting to environmentBlue – water molecules, easily pass through membraneRed – large (or charged) molecules, can’t pass through membrane
13 Isotonic Solutions - “Iso” equal Cells that are in equilibrium with the surrounding solution do not experience osmosis.These cells have the same concentration of solute (and water) as the surrounding solution
14 Hypotonic Solutions – “hypo” lower [solute] (solute concentration) is lower outside the cellMore water outside, so water moves into the cell, to try to reach equilibriumThe cell swells with the extra water.Animal cells may swell so much, they may burst (especially in pure water)Plant cells – cell swells and membrane pushes against the cell wallLike celery in water – crisp/ rigid from pressure on cell walls
15 Hypertonic Solutions - “hyper” higher [solute] is higher outside of the cell.Less water outside the cell, more inside. Water moves out of the cell.Animal cells shrivel because of water loss.Plant cell membranes move away from cell wall as water moves out.Why plants wilt.
16 Other Forms of Transport Active Transport – (needs energy)Large particle transportEndocytosis – cell surrounds molecule(s), which are then engulfed by celldoesn’t pass through membraneExocytosis - expulsion/secretion of materials. Opposite of endocytosis
17 Active Transport (con’t) Movement of molecules against (up) the concentration gradientFrom areas of lower concentration to areas of higher concentrationFor instance, if a cell needs a high concentration of something (that would normally diffuse OUT of cell)