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DO NOW . What is the function of the golgi apparatus? . Cell Boundaries . Cell Membrane Cell Wall . Cell Membrane . Regulates what enters and leaves the cell and also provides protection and support. Nearly all cell membranes are double-layered sheets called lipid bilayer .

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  1. DO NOW What is the function of the golgi apparatus?

  2. Cell Boundaries • Cell Membrane • Cell Wall

  3. Cell Membrane • Regulates what enters and leaves the cell and also provides protection and support. • Nearly all cell membranes are double-layered sheets called lipid bilayer. • There are two layers of lipids. • Gives cell membranes a flexible structure that forms a strong barrier between the cell and its surroundings.

  4. Cell Membrane (continued) • Most cell membranes contain protein molecules that are embedded into the lipid bilayer. • Carbohydrate molecules are attached to the proteins • Fluid Mosaic Model

  5. Cell Membrane • Some proteins form channels which allow materials in and out of the cell. • Carbohydrates act like identification cards which allows cells to know one another.

  6. Cell Walls • Present in plants, algae, fungi, and many prokaryotes. • Outside the cell membrane • Most are porous enough to allow water, oxygen, carbon dioxide, and certain other substances to pass through easily. • Main function is to provide support and protection for the cell.

  7. Cell Walls (continued) • Made from fibers of carbohydrate and protein. • Materials for the cell wall are produced within the cell then released to the surface of the cell membrane. • Plant cell walls are made mostly of cellulose. • Cellulose is the main part of wood and paper.

  8. Diffusion through Cell Boundaries • Living cells are in a liquid environment that it needs to survive. • One of the most important functions of the cell membrane is to regulate the movement of materials from the liquid outside the cell to the inside and vice versa.

  9. Measuring Concentration • Cytoplasm of a cell contains a solution of many different substances in water. • The concentration of a solution is the mass of a solute in a given volume of solution. • 12 grams of salt is dissolved in 3 liters of water; 12grams/3liters = 4 grams/liter

  10. Diffusion • In a solution particles move constantly. • Particles move from an area of high concentration to an area of low concentration, this is called diffusion. • When the concentration of the solute is the same throughout a system, the system has reached equalibrium. • Because diffusion depends on random particle movements, substances diffuse across membranes without requiring the cell to use energy.

  11. Permeable Versus Impermeable • If a substance can diffuse across the membrane it is said to be permeable • If a substance cannot diffuse across the membrane, then the membrane is impermeable to that substance • Most biological membranes are selectively permeable- some substances can pass and some cannot. • Selectively permeable can also be referred to as semipermeable.

  12. Osmosis • Some substances are too large or strongly charged to cross the membrane by diffusion. • The diffusion of water across a selectively permeable membrane. • The movement of water to create equal concentrations on either side of a semi permeable membrane. Water will tend to move until equilibrium is reached.

  13. Osmosis (continued) • Isotonic solutions- solutions on either side of the membrane have an equal concentration. • Hypertonic solutions- the solution has a higher concentration than the cell (water will move out of the cell) • Hypotonic- the solution has a lower concentration than the cell (water will move into the cell)

  14. Osmotic Pressure • Organisms must be able to control their intake and removal of water. • Osmosis exerts a pressure on the hypertonic side of the cell. • Look at the chart on page 186

  15. Facilitated Diffusion • Cell membranes have protein channels that acts as carriers for some molecules to help them get into and out of the cell. • The channels are said to help or facilitate the motion of certain molecules. • The example in the text is glucose

  16. Active Transport • Movement against a concentration gradient • Requires energy • Usually carried out by transport proteins or “pumps” • Larger molecules are moved by endocytosis and exocytosis • Movement of larger molecules sometimes involve the change in shape of the cell membrane

  17. Molecular Transport • Changes in protein shape seem to create the pumping process • A large portion of the energy used by cells daily is for active transport

  18. Endocytosis • The process of taking material into the cell by means of infolding, or pockets, of the cell membrane • The pocket breaks away from the cell membrane and forms a vacuole within the cytoplasm • Two examples are • Phagocytosis-cell eating • Extensions of cytoplasm surround a particle and package it within a food vacuole. Then the cell engulfs (eats) it. • Pinocytosis • Liquid filled pockets pinch off and form vacuoles in the cell

  19. Exocytosis • The release of large amounts of material • The membrane of the vacuole surrounding the material fuses with the cell membrane forcing the material out of the cell.

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