Biological membranes

• All cells and organelles are surrounded by partially permeable membrane composed of a sea of phospholipids with protein molecules between the phospholipid molecules.
• The main

  function of the membrane is controlling the

  movement of substances in and out of the

  cell/organelle.

  
• However, it also contains

  receptors for other molecules such as hormones and enables adjacent cells to stick together.

  
• The fluidity of the membrane and the mosaic arrangement of the protein give the structure of the membrane its name – fluid mosaic model.

  
• What are the types of movements in the cell membrane?

  Diffusion

  Facilitated diffusion

  Osmosis

  Active transport

  Axocytosis
• Diffusion is the passive movement of small, non-polar lipid soluble molecules such as

  carbon dioxide and oxygen from an area of high concentration to an area of low

  concentration. The molecules move directly through the phospholipid bilayer.
• Facilitated diffusion requires a channel protein in the cell membrane to transport

  polar molecules, charged and water soluble molecules across the membrane.
• Osmosis is the diffusion of water molecules from an area of low solute concentration to an area of high solute concentration through a partially permeable membrane
• Osmosis is the diffusion of water molecules from an area of high water potential to an

  area of low water potential through a partially permeable membrane.
• Active transport can transport all types of molecules through carrier proteins from an area of low concentration to an area of high concentration. However, this process

  requires energy in the form of ATP.
• Exocytosis and endocytosis transport large particles and bulk transport . The particles

  are enclosed in vesicles made from the cell surface membrane and transported into the cell in endocytosis. In exocytosis, vesicles containing large particles are fused with the cell surface membrane
• What are the three factors of gas exchange by diffusion?

  Surface area

  Diffusion distance

  Diffusion gradient