Big+Idea+11


 * Big Idea 11: Cell Membrane Structure, Diffusion, Osmosis, Endocytosis, Exocytosis**

__Summaries__ //Cell Membrane:// The cell membrane is the layer that separates the interior of a cell from it's external environment. It serves many different functions. In animal cells, the cell membrane is the only thing dividing the external environment from the interior. However in plant cells, there exists a cell wall as well as a membrane.

//Diffusion:// Diffusion is the movement of molecules from a high concentration area to a low concentration area. This does not require any use of energy, and is purely passive.

//Osmosis:// Diffusion of materials through a semi-permeable membrane, from

//Endocytosis:// Endocytosis is the process which a cell absorbs materials outside the cell by engulfing the material with their cell membrane. It is an important process for cells because some materials needed by cells are too large to

//Exocytosis:// The process by which materials inside a cell are released through the membrane.

__Cell Membrane__ The cell membrane is the main layer between the interior of a cell and its external environment. It is a semi-permeable membrane, thus allowing many different functions to occur, such as diffusion, osmosis, endocytosis, and exocytosis. It is composed of a lipid bi-layer with protein channels embedded in it. The protein channels allow the cell to receive and send messages to and from other cells in the vicinity. It acts as the first defense to foreign particles that can damage the cell, or render it incapacitated. The cell membrane is selectively premeable so only needed material is allowed in, keeping waste out.

__Diffusion__ Diffusion is the process of the movement of molecules from high concentration to a low concentration area. This is a passive operation, thus does not require and active use of energy. There must be a membrane that allows various particles large and small to pass through. Diffusion has many useful functions in the human body.

__Osmosis__ Osmosis is the process of movement of water through a semi-permeable layer such as a cell membrane. It can be passive, however, active use of energy to move water from a lower concetran area to a high concentration area. This is important because cells require water to function, thus, osmosis is an important function is retaining the vitality of body cells.

__Endocytosis__