Cell Structure (Chapter 7- Section 2) (part 2) THINK ABOUT IT -When thinking about how cells move materials in and out, it can be helpful to think of a cell as a country. The boundaries of a country are its borders, and nearly every country tries to regulate and control the goods that move across those borders. Cells have their own borders, which separate the cell from its surroundings and also determine what comes in and what goes out. How can a cell separate itself from its environment and still allow material to enter and leave? By the cell membrane Cell Membrane Function: • Regulates what enters and leaves the cell (cell membrane is selectively permeable or semipermeable, this meaning some substances can pass across them and others cannot) • Provides protection and support Structure: Fluid Mosaic Model. It consists of: 1. Phospholipid bilayer – two layers of phospholipids (having hydrophilic phosphate heads and hydrophobic lipid tails) 2. Proteins run through the layers (Some proteins form channels and pumps that move material across the cell membrane). 3. Carbohydrates are attached to some of the proteins (carbohydrates act like I.d. cards, allowing cells to identify one another) The Cell Theory: Cell theory has three parts: 1. All living things are made of one or more cells. 2. Cells are the basic units of structure and function in organisms. 3. All cells arise from existing cells.