Structure and Function of Organelles cell plasma membrane

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Structure and Function of Organelles cell
(plasma) membrane

• semi-permeable membrane which regulates the
  passage of substances into and out of the cell
• composition protein molecules dispersed
  throughout a double layer of lipid (fluid mosaic)

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Animal Cell
Eukaryotic Cell
Eukaryotic Cell
Plant Cell
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Factors affecting permeability of cell membrane
to a particular substance

• 1. molecular size of the substance cell
  membrane generally is permeable to small
  molecules such as water (H2O), carbon dioxide
  (CO2), glucose (C6H12O6) and amino acids

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Factors affecting permeability of cell membrane
to a particular substance

• 1. molecular size of the substance
• 2. electrical charge on the atom or molecule of
  the substance
  

Na



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Cl-
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Factors affecting permeability of cell membrane
to a particular substance

• 1. molecular size of the substance
• 2. electrical charge on the atom or molecule of
  the substance
• 3. solubility of the substance in water

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Factors affecting permeability of cell membrane
to a particular substance

• 1. molecular size of the substance
• 2. electrical charge on the atom or molecule of
  the substance
• 3. solubility of the substance in water
• 4. solubility of the substance in lipid

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What determines the direction of the movement of
molecules (diffusion) across the cell membrane?

• concentration of substances on each side of the
  membrane

Click on image for movie.
Diffusion is a form of passive transport.
(no energy required)
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Osmosis

• diffusion of water through a semi-permeable
  membrane from an area where the water molecules
  are more concentrated to an area where the water
  molecules are less concentrated

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Cells

• exposed to an isotonic solution will neither lose
  nor gain water
• exposed to a hypotonic solution will swell due to
  the uptake of water by the cell
• exposed to a hypertonic solution will shrink due
  to the loss of water from the cell

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Active transport requires energy.

• A transport protein actively pumps a specific
  solute across a membrane against the solutes
  concentration gradient i.e., away from where the
  solute is less concentrated. Membrane proteins
  use ATP as their energy source for active
  transport.

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energy
energy