Membranes - the basics

• Basic structure in all cell membranes is the same
• Membrane Is partially permeable so controls entry and exit of substances in and out of the cell
• Transport of substances important because constant concentration must be maintained inside the cell, waste products must be removed and substances required by the cell must be transported in
• phospholipids in the membrane allows the movement of small, non polar molecules by simple diffusion
• osmosis is the transport of water by a special form of diffusion
• Larger molecules transported by channel and carrier protein molecules in the membrane by process called facilitated diffusion
• Proteins also act as carrier molecules by active transport
• endocytosis And exocytosis are special forms of active transport
• Organelles contain membrane structures which are the site of chemical reactions

  • like chloroplasts contain thylakoids

  • mitochondria contains cristae