The cell membrane and transport

What you will be able to do

• Describe the fluid mosaic structure of the plasma membrane and explain why it is selectively permeable.
• Sort a transport process into passive or active based on whether it needs energy.
• Name each passive transport route, diffusion, facilitated diffusion, and osmosis, and say what each one moves.

What the lesson concludes

• The membrane is a phospholipid bilayer with hydrophilic heads facing out and hydrophobic tails facing in.
• Passive transport follows the concentration gradient and costs no cellular energy.
• Active transport moves a substance against its gradient and always costs ATP.
• Osmosis is simply the diffusion of water across a selectively permeable membrane.
• Endocytosis and exocytosis move whole particles or fluid across the membrane in vesicles, not through channels.