Cell Membrane What is it? – Barrier that separates cell from external environment – Composed of...
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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