2Homeostasis – the maintenance of internal stable conditions The cell membrane keeps the cell in balance.
3Membrane FunctionsProvides a selectively permeable barrier around the cell.Controls the passage of substances in and out of the cell.Maintains homeostasis for the cell.
4Membrane Structure Phospholipid bilayer (nonpolar) Membrane proteins: act as transport channels.Carbohydrate chains: act as “ID” tags for the cell.Cholesterol: provides stability for the membrane.
5Phospholipid Bilayer Phospholipid Bilayer Phospholipids: phosphate head and lipid tail.Phospholipid Bilayer: two layers.Hydrophilic = attracts waterinside celloutside cellPhosphateHeadLipid TailsPhospholipid BilayerHydrophobic = repels water
6So what needs to get across the membrane? The cell membrane is semipermeable, which means only some material can get in or out.So what needs to get across the membrane?SugarLipidsAminoAcidsO2H2OSaltWaste
7How do you build a semi-permeable cell membrane? Channels are made of proteins.Proteins act as doors in the membrane.BilipidMembraneProtein Channels in Bilipid Membrane
8Diffusion Molecules move from HIGH to LOW concentration; this continues until equilibrium is reached.Simple diffusion: directly through membrane.Facilitated diffusion: help through a protein channel.NO energy needed!!HIGHLOW
9Active TransportCells use energy to move against concentration gradient - from LOW to HIGH.Particles that are polar (charged) must move through a protein channel.Use protein pumprequires energy (ATP)Plants have nitrate & phosphate pumps in their roots.Why?Nitrate for amino acidsPhosphate for DNA & membranesNot coincidentally these are the main constituents of fertilizer.ATP
10Transport of Molecules Endocytosis: takes material into cell by cell membrane making pockets.Phagocytosis – “cell eating”; cell engulfs particlesPinocytosis – cell takes in liquid from surrounding environment.Exocytosis: process forcing contents out of the cell.
14Types of Cellular Transport PASSIVEDoes NOT require energyGoes with the concentration gradient (high to low)Simple Diffusion, Facilitated DiffusionACTIVERequires energy from ATPGoes against the concentration gradient (low to high)Active Transport, Endocytosis, Exocytosis
15Osmosis movement of water across cell membrane. HIGH H2OLOW H2O
16Effects of Osmosis on Cells (osmotic pressure) Hypertonic: higher concentrations of solute; less H2O.Isotonic: equal concentrations of solute.Hypotonic: lower concentrations of solute; more H2O.