Cell Membrane: Structure and Function

In or Out?  1. What are some things that can pass through a window screen?  2. What are some things that cannot pass through a window screen? Why is it important to keep these things from moving through the screen?  3. The cell is surrounded by a cell membrane, which regulates what enters and leaves the cell. Why is it important to regulate what moves into and out of a cell? Interest Grabber

Outside of cell Inside of cell (cytoplasm) Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains Section 7-3 Figure 7-12 The Structure of the Cell Membrane

Cell Membrane  Function = controls what enters the cell and what leaves the cell  Made of a lipid bilayer  Has proteins  Has some carbohydrates, which help with identification  Is fluid (fluid mosaic model)

Diffusion  Def. of diffusion = Spreading of molecules in a given space.  What happens? -Substances move from an area where there is more of them to an area where there is less of them

Diffusion  Def. of permeable = membrane that lets substances pass through it  Cell membrane is selectively permeable, which means that it lets some things in but does not let other things in  Substances keep moving till there is about equal amounts of them on both sides of the membrane

High Concentration Low Concentration Cell Membrane Glucose molecules Protein channel Section 7-3 Diffusion

Factors that Affect Diffusion  Amounts of substances involved  Temperature  Pressure  Stirring -speeds up the rate of diffusion

Diffusion  Diffusion Video Diffusion Video

Osmosis  Def. of osmosis = movement of water from greater to lesser

Figure 8.11 Osmosis

Figure 8.12 The water balance of living cells

Osmosis  Water goes into a cell causing it to swell up and burst = plasmoptysis  Water leaves the cell causing it to shrink = plasmolysis  *Know the difference between plasmoptysis and plasmolysis!*

Osmosis  Some one-celled organisms have a contractile vacuole that pumps water out of a cell  In plants, as water goes into the cell, it builds up pressure that pushes against cell wall. This is called turgor pressure.

Contractile Vacuole

Osmosis  Osmosis Video Osmosis Video

Passive Transport  NO ENERGY NEEDED!  Is the movement of small molecules in and out of a cell  Molecules go from greater to lesser (=with concentration gradient)  Examples: amino acids, fatty acids, glycerol, simple sugars (glucose)

Passive Transport

 Passive Transport Video Passive Transport Video

Active Transport  ENERGY NEEDED!  Molecules go from lesser to greater (=against concentration gradient)  This is when large molecules are pulled through the cell membrane by the use of ENERGY  Do not fully know how it works

Molecule to be carried Molecule being carried Energy Section 7-3 Figure 7-19 Active Transport

Active Transport  Active Transport Video Active Transport Video

Endocytosis and Exocytosis  Def. of endocytosis = process by which cells take in large molecules from the outside -ex. pinocytosis and phagocytosis Def. of exocytosis = process by which cells get rid of large molecules in the cell

Pinocytosis  Pinocytes are pockets on the cell membrane.  Large molecules fall into the pockets and get turned into food vacuoles inside the cell

Pinocytosis

Phagocytosis: Engulfing  This is when large molecules are surrounded and pulled into the cell  Examples: amoeba, white blood cells called phagocytes  This is the same method used by white blood cells to trap bacteria in our blood

Phagocytosis: Engulfing

 Endocytosis and Exocytosis Video Endocytosis and Exocytosis Video Endocytosis and Exocytosis