Cell Membrane

• What is it?– Barrier that separates

cell from external environment

– Composed of two phospholipid layers• Other molecules are

embedded in the membrane

Cell Membrane– Has two major functions

• Forms boundary between inside and outside of the cell

• Controls passage of materials

– Selectively permeable• Some molecules can cross

while others cannot

Diffusion and Osmosis

• How does material move across a cell membrane?

• Passive transport- does not require energy- two types– Diffusion– Osmosis

• Molecules diffuse down a concentration gradient

Diffusion and Osmosis• Osmosis- diffusion of water molecules across a membrane• 3 types of solutions

– Isotonic– Hypertonic– Hypotonic

Diffusion and Osmosis

• Cell membrane channels help move molecules across

• Facilitated diffusion- diffusion through transport proteins

Active Transport, Endocytosis, and Exocytosis

• Active transport- transportation of materials against the concentration gradient– Requires energy (ATP)– Occurs through

transport protein pumps– Use it to main

homeostasis

Active Transport, Endocytosis, and Exocytosis

• Endocytosis- carry larger molecules into the cell using vesicles– Phagocytosis- moves particles or whole cells in– Pinocytosis- moves fluids in

• Exocytosis- taking larger molecules out of the cell