Types of transport across the membrane

Transport across the membrane 

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  • Created by: sian
  • Created on: 19-12-12 16:10

Diffusion

  • Passive process
  • The net movement of molecules from a high concentration to a low concentration until an equilibrium has been reached, through a partially permeable membrane
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Facilitated Diffusion

  • Passive process 
  • The movement of molecules/ions from a region of high concentration to a region of low concentration, through a partially permeable membrane, with the use of carrier and channel proteins 
  • It allows the faster movement of molecules 
  • Charged particles and ions cannot pass through the cell membrane because they are relitively insoluble in lipids 

Channel Protiens: 

  • Lined with polar groups allowing charged ions to pass through 
  • Only particular ions are able to pass through
  • Open and close according to the needs of the cell 

Carrier Proteins: 

  • Allows diffusion of larger molecules across the membrane e.g. amino acids and sugars 
  • Particular molecules attach to the protein. The binding site causes the protein to change shape; releasing molecules through the membrane
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Active Transport

  • Requires ATP - Non passive process
  • The movement of molecules and ions from a high concentration, to a low concentration against a concentration gradient -> Ions and molecules are able to move in the opposite direction that diffusion occurs 
  • Anything that affects the respiratory process affects active transport 
  • Occurs through the carrier protein
  • Processes that require active transport include: Protein synthesis and muscle contraction 
  • Examples of Active transport - The iron pump
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Osmosis

  • The movement of water, from a region of high water potential to a region of low water potential, down a concentration gradient, through a partially permeable membrane
  • Water potential is the potential for water to move out of a solution
  • WP is measure in KiloPascals 
  • Highest WP is 0 (distilled water)

Osmosis in Plant Cells

 If water moves into the cell, it expands causing the cytoplasm to push against the cells wall - the pressure builds up resisting the entry of anymore water - becomes TURGID

INCIPIENT PLASMOLYSIS  - the protoplast begins to peel away from the cell wall 

PLASYMOLYSIS - the protoplast completely pulls away from the cell wall 

Osmosis in Animal Cells

In HYPETONIC solutions the cell becomes CRENATED  

In ISOTONIC solutions the cell remains the same 

IN HYPOTONIC solutions LYSIS occurs in the cell 


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Bulk Transport

The cell transports in bulk into the cell ENDOCYTOSIS and out of the cell EXOCYTOSISENDOCYTOSIS - englufing the materials the plasma membrane brings into the cell inside a vesicle  PHAGOCYTOSIS - where a cell can obtain solid materials that are too large to be taken in by diffusion or active transport  A lysosome fuses with the vesicle, enzymes digest the solid material and the products are absorbed into the cytoplasm, phagocytes destroy bacteria and remove debris by phagocytosis PINOCYTOSIS - entry of liquid by the sam mechanism as phagocytosis except vesicles are smaller  EXOCYTOSIS - substances leaving the cell after being transported though the cytoplasm in a vesicle. Digestive enzymes are often secreted in this way

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