Cell Boundaries

I. What is the Function of The Plasma Membrane? Separate cell from its surroundings Provides protection and support Regulates what enters and leaves the cell ** The cell Membrane is selectively permeable. That means it will allow only certain materials to pass through. ** Homeostasis within the cell is maintained by controlling the concentrations of water, glucose, nutrients, and waste within a cell.

II. Structure of the Plasma Membrane? A.Lipid Bilayer: double layered sheet of lipids * Gives cells flexibility and forms a strong barrier * Lipids have 3 fatty acids and 1 glycerol molecule, but in the cell membrane, one fatty acid is replaced by a phosphate group to create a phospholipid molecule

Phospholipids have a polar head which attracts things, and a non- polar tail which repels things. * phosphates: hydrophilic (water loving) * Fatty Acids: hydrophobic (water fearing)

In between the phospholipid molecules are protein molecules. They determine what can enter across the membrane.

III. Cell Wall A.Function: Provide support and protection B.Most are porous enough to allow H2O, CO2 and certain other substances to pass through C.Composed of carbohydrates and proteins * Made inside cell, released, and assembled outside the cell D.Plant cell walls are composed of cellulose * A tough carbohydrate fiber * Ex. Wood & Paper (main component is cellulose)

Cellular Transport ** All objects, including molecules, have kinetic energy, or energy of motion. Because of this energy, molecules are always moving from areas of high concentrations to areas of low concentrations

I. Passive Transport A.Diffusion: The movement of particles from an area of high concentration to an area of low concentration * Diffusion cannot occur unless a substance is in higher concentrations in one region than it is in another. *The differences in concentration of a substance across space is called a concentration gradient *Eventually, the molecules will be evenly distributed. There will be movement of the molecules but no change in gradient. This condition is called dynamic equilibrium * Only small particles move across the membrane, so little energy is used

Example – There are 100 people stuffed into this room; there are only 10 people in the room next door. Where would you move?

Does the diffusion of more than one kind of particle work together or separately? Do the particles stop moving once equilibrium is reached?

Does the diffusion of more than one kind of particle work together or separately? NO!

B. Osmosis = The diffusion of water through a selectively permeable membrane. Involves large, charged (+/-) molecules No energy is used

Since water passes freely across the membrane, how can the cell control the direction of osmosis? Water will follow the solutes!

??

Which way will the water move?

WHY?

Types of Solutions A.Isotonic: a solution in which the concentration of dissolved substances is the SAME as the concentration inside the cell. B.Hypotonic: a solution in which the concentration of dissolved substances is LOWER than concentration inside the cell Results in turgor pressure: pressure exerted on cell C.Hypertonic: a solution in which the concentration of dissolved substances is HIGHER than the concentration inside the cell A cell will lose water and result in plasmolysis: loss of turgor pressure

Water Balance in Cells

C. Facilitated Diffusion Movement of specific molecules across cell membranes through protein channels (help molecules pass through) Sugars and amino acids are too big to enter by diffusion. The proteins embedded in the bilayer help these molecules to pass across the membrane by providing them with a “door”

IV. Active Transport A process that requires energy to move molecules across the cell membrane against the concentration gradient (low to high) Transport is carried out by transport proteins or “pumps” that are found in the membrane

A.Molecular Transport Carries ions and other small molecules ex: calcium, sodium, potassium Changes occur in membrane/protein shapes

B.Endocytosis Taking materials INTO the cell by infoldings, or pockets, of the membrane Pocket breaks away from the membrane and forms a sort of vacuole * Phagocytosis: cell eating (food) * Pinocytosis: cell drinking (liquid)

C. Exocytosis Releasing materials OUT of the cell The membrane of the vacuole joins with the cell membrane, forcing contents of the vacuole out of the cell

Review of passive and active transport: ?

?

?

?