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PASSIVE TRANSPORT Joud & Anoud

PASSIVE TRANSPORT Joud & Anoud. DIFFUSION. Recap: DIFFUSION. Diffusion is the movement of liquid or gas molecules from an area of high concentration to an area of low concentration- they pass down their concentration gradient.

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PASSIVE TRANSPORT Joud & Anoud

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  1. PASSIVE TRANSPORT Joud & Anoud DIFFUSION

  2. Recap: DIFFUSION Diffusion is the movement of liquid or gas molecules from an area of high concentration to an area of low concentration- they pass down their concentration gradient. This occurs because of random motion of molecules and their high energy.

  3. After the molecules are in uniform distribution; they don’t stop moving. However, the movement no longer causes a net change in concentration because equal numbers of molecules are moving in all directions.

  4. For many small molecules like oxygen and carbon dioxide, the cell membrane is no barrier and they can freely diffuse across it. Diffusion is an example of passive transport (where no energy is required)

  5. Polar molecules and charged ions are dissolved in water but they can not diffuse freely across cell membranes due to the hydrophobic nature of the phospholipids that make up the lipid bilayers. Only small non polar molecules, such as oxygen can diffuse easily across the membrane. All polar molecules are transported across membranes by proteins.

  6. Passive Transport:FACILITATED DIFFUSION Definition: Facilitated Diffusion is the transport of substances (large in size or with a strong positive/negative charge) across a membrane by a trans-membrane protein molecule. The transport proteins tend to be specific for one molecule, so substances can only cross a membrane if it contains the appropriate protein. As the name suggests, this is a passive diffusion process, so no energy is involved and substances can only move down their concentration gradient.

  7. FACILITATEDDIFFUSION - 1 There are 2 types of facilitated diffusion, one of them is by CHANNEL PROTEINS. Channel Proteins form a water-filled pore or channel in the membrane. This allows charged substances (usually ions) to diffuse across membranes. Most channels can be gated (opened or closed), allowing the cell to control the entry and exit of ions. Each type of channel protein allows one particular molecule through (depending on shape) The channels open when a molecule is present or there is an electric change across the membrane.

  8. FACILITATED DIFFUSION - 2 CARRIER PROTEINS, these are found on the outside of membranes- they are also specific for each molecule. Carrier Proteins have a binding site for a specific solute and constantly flip between two states so that the site is alternately open to opposite sides of the membrane. The substance will bind on the side where it at a high concentration and be released where it is at a low concentration.

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