Cell Membrane and Transport

Plasma Membrane – Protects the cell from its surroundings

• • • • • Selectively permeable – negotiates transport of molecules in and out of the cell to maintain homeostasis; some pass, some do not

Phospholipid

• polar head – hydrophilic (water-loving)
• non-polar tail – hydrophobic (water-hating)

Phospholipid bilayer

Many cells have a cell wall around the membrane also, but not animal cells.

Passive transport – no energy required, follows the concentration gradient

• • • • diffusion – through the membrane
      • facilitated diffusion – uses protein channels

Active transport – energy required, molecule movement against concentration gradient

• • • • protein pumps – Sodium/Potassium pump
      • bulk transport
        • endocytosis – vesicle forms to take the material into the cell
        • exocytosis – vesicle forms to release material from the cell