The Cell Membrane

Function The cell membrane selectively regulates the entry and exit of materials. This helps cells in maintaining homeostasis. Fluid Mosaic Model: double phospholipid layer in which large proteins are imbedded.

Structure

What CAN pass through the cell membrane? -Small molecules such as: -dissolved gasses -water -simple sugars -amino acids (building blocks of proteins)

What CANNOT pass through the cell membrane? Large molecules such as: Starches (complex carbohydrates) Proteins (many amino acids linked together)

AIM- How do molecules move across the cell membrane? HW- P 189 #1-5

Passive Transport 1. Simple Diffusion: movement of molecules from an area of high concentration to an area of low concentration. (does NOT require energy) Diffusion animation

OSMOSIS -diffusion of WATER molecules from an area of high concentration to an area of low concentration. (does not require energy) The cytoplasm of cells is composed mostly of water that contains many different dissolved particles, such as salt. Water will move to where there is a high concentration of particles.

(does not require energy) Facilitated Diffusion: diffusion through protein channels in the cell membrane. (does not require energy) Facilitated difusion animation

Active Transport Movement of molecules from a region of LOW concentration to a region of HIGH concentration. Requires ENERGY in the form of ATP! Active transport animation

OSMOSIS in more detail: The cytoplasm of cells is composed mostly of water that contains many different dissolved particles, such as salt.  these are called solutes. Water will move from an area of higher water concentration to an area of lower water concentration. Water will move to where there is a high concentration of particles.

Osmosis in detail: 3 Types of possible solutions Isotonic-The rate of osmosis into the cell is exactly the same as the rate of osmosis out of the cell. There is no net movement of water.

Hypotonic Solution The concentration of water is lower inside the cell and higher outside the cell. There is a higher concentration of molecules inside the cell. Water will move from outside the cell into the cell.

Hypertonic Solution Concentration of water is higher inside the cell than outside. There is a higher concentration of molecules outside the cell. Water will flow from inside the cell to outside the cell.

REMEMBER… Simple rule to remember-SALT SUCKS! When salt is concentrated inside or outside the cell, it will draw water in its direction. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

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