Transport across Membranes

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Transport across Membranes
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Diffusion

• The random movement of atoms, molecules and small
  particles from an area of high concentration to
  an area of low concentration. No energy (ATP)
  required.

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Osmosis

• Diffusion of water across a membrane

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• Permeable able to pass through
• Impermeable not able to pass through

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Semipermeable Membrane or Differentially Permeable

• Some substances can pass through and others cant
  
• Either due to their size or electrical charge
• Ex. Plasma membrane

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Facilitated Diffusion

• Sometimes, large molecules cannot cross the
  plasma membrane, and are "helped" across by
  carrier proteins - this process is called
  facilitated diffusion

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Active Transport

• Active Transport - this type of transport
  requires that the cell use energy, because
  substances are moving against the concentration
  gradient.

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Sodium Potassium Pump
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Endocytosis

• In endocytosis, the cell engulfs some of the
  material around it. A portion of the plasma
  membrane is invaginated and pinched off forming a
  membrane-bound container

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Exocytosis

• A membrane bound part of the cell is moved to the
  cell membrane and its contents are ejected from
  the cell.

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Phagocytosis

• The cell engulfs those things that it wants
• Occurs sporadically and in only a few types of
  cells
• Forms vacuoles
• cell eating

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Pinocytosis

• The engulfed material is relatively small
• Occurs in nearly every cell
• cell drinking

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Isotonic

• If the concentration of solute (salt) is equal on
  both sides, the water will move back in forth but
  it won't have any result on the overall amount of
  water on either side.
• Iso- means the same

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Hypertonic

• The word "HYPER" means more, in this case there
  are more solute (salt) molecules outside the
  cell, which causes the water to be sucked in that
  direction.
• In plant cells, the central vacuole loses water
  and the cells shrink, causing wilting.
• In animal cells, the cells also shrink.
• In both cases, the cell may die.
• Egg in salt water is hypertonic and will lose
  water
• Hyper- means too much or above

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Hypotonic

• The word "HYPO" means less, in this case there
  are less solute (salt) molecules outside the
  cell, since salt sucks, water will move into the
  cell.
• The cell will gain water and grow larger. In
  plant cells, the central vacuoles will fill and
  the plant becomes stiff and rigid, the cell wall
  keeps the plant from bursting
• In animal cells, the cell may be in danger of
  bursting, organelles called CONTRACTILE VACUOLES
  will pump water out of the cell to prevent this.
• The egg in fresh water is hypotonic and water
  will enter
• Hypo- means too little or low

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