2 Cell Membrane -Thin flexible layer around cell -Controls what goes in or out of cell-Provides protection and support-Made of a phospholipid bilayer—two layers of lipids-Proteins are embedded in bilayer-These help move materials across the cell membrane
3 Phospholipids in cell membrane are arranged in two layers with nonpolar fatty acid “tails” together. The polar “heads” face the watery environments found inside and outside the cell.This structurecreates a barrierthat helps the cellmaintain homeostasis
5 The cell membrane can be described as a Fluid Mosaic Model. The phospholipids in the bilayer float together like beach-balls on water. The lipids are in constant motion, and can slide past each other, and other molecules, like proteins can move in between them.
6 Figure 7-12 The Structure of the Cell Membrane Section 7-3Outsideof cellInside(cytoplasm)CellmembraneProteinsProteinchannelLipid bilayerCarbohydratechains
7 Movement across Cell Boundaries Passive TransportDoes not require energyMaterials move from area of high concentration to area of low concentration until equilibrium * is reachedThree types of passive transport
8 Diffusion is the movement of particles from where they are more concentrated* to where they are less concentrated.It occurs due to the random movement of particles.It continues until a dynamic equilibrium is reached—the concentration is the same on both sides of the membrane.Particles still move in both directions across membrane, but there is no further change in concentration.
12 Isotonic: concentrations of the water are the same both inside and outside the cell; water enters and leaves cell at same rate; cell size doesn’t changeHypotonic: lower water concentration inside the cell than outside; water enters the cell; cell swellsHypertonic: lower water concentration outside the cell than inside; water moves out of the cell; cell shrinks
13 3. Facilitated Diffusion is when large molecules like glucose move across the cell membrane through protein channels: protein molecules embedded in the lipid bilayer. They are specific to different substances and have carbohydrate marker chains on them that act as identification cards. The protein channels act like an open gate for the substance they are marked for.
16 Figure 7-12 The Structure of the Cell Membrane Section 7-3Outsideof cellInside(cytoplasm)CellmembraneProteinsProteinchannelLipid bilayerCarbohydratechains
17 Active Transport Requires energy from the cell Materials move from an area of lower concentration to an area of higher concentration.It is usually done by transport proteins or “pumps” found in the cell membraneThree types of active transport
18 Sodium/Potassium Pump In animal cell membranesUses energy to move Na+ out of cell and K+ into cell
19 Endocytosis:Process of moving large molecules into a cellMaterials enter the cell by making folds in the cell membrane.Requires energy
20 Exocytosis:Process of moving large materials out of the cell.Materials leave the cell by fusing vesicles with the cell membrane.Requires energy