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Biology
The Cell Membrane
Pg. 272 ­ 274
1. The cell is an open system with both matter and energy flowing in and out. The three roles of the cell membrane is to:
a. Maintain equilibrium (balance) inside the cell
b. Transport materials in and out of the cell
c. Recognize foreign cells and communicate with other cells
2. The cell membrane consists of three components:
a. The phospholipid bi­layer is a double layer of lipids (fat). Each lipid has a phosphate molecule attached. The lipids are hydrophobic, which means that they repel water. The phosphate molecules are hydrophilic and attract water. This maintains the water inside the cell as well as separates it from the watery environment that surrounds it. The cytoplasm can move and flow inside the cell membrane.
b. Proteins are suspended in the phospholipid bi­layer. They may be attached to the outside, inside or run through the bi­layer into the inside of the cell. The specific functions of these proteins are
1. Helps maintain membrane structure
2. Chemically recognizes and transports substances in/out of the cell
3. Form pores in the cell membrane that determine the size of particles that can go in/out.
c. Sugar molecules are sometimes attached to the surface proteins. These sugars enable cells to recognize foreign substances and enable the cells to interact with each other.
http://www.wisc­online.com/Objects/ViewObject.aspx?ID=ap1101
3. Draw and label the components of the cell membrane: (pg. 273)
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The role of the Cell Membrane in Transport: (pg. 274)
Define the following words:
Permeable: Something that lets all things pass through
Semi­permeable: A membrane that allows only certain particles through
Impermeable: Something that lets nothing pass through
The cell membrane is semi­permeable. It selectively lets some substances through while keeping other substances out.
Some substances that move into and out of cells are:
Water
Wastes
Potassium
O2
Hormones
Trace minerals
CO2
Enzymes
Bacteria/viruses
glucose
Sodium Other cells
Some substances move in/out of the cell passively ­ without the cell expending energy, or actively ­ the cell uses energy to push substance out or pull substances in.
1. Passive transport ­ diffusion, osmosis, and facilitated diffusion
2. Active transport ­ active transport, Endocytosis, Exocytosis .
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