Passive and Active Transport

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Passive and Active Transport
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Passive Transport

• Cell membranes help organisms maintain
  Homeostasis by controlling what substances may
  enter or leave cells
• Doing this WITHOUT energy is called passive
  transport
• Diffusion
• Osmosis

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Diffusion

• The simplest form of passive transport
• Does not require energy
• Is the movement of molecules from an area of HIGH
  concentration to an area of LOW concentration

High concentration of dye
Low concentration of dye
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Osmosis

• The diffusion of WATER over a semi-permeable
  membrane
• Does NOT require energy
• From HIGH concentration of WATER to LOW
  concentration of WATER

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Osmotic Conditions

• Isotonic
• Hypertonic
• Hypotonic

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Isotonic

• In an Isotonic solution
• The concentration of solutes inside the cell are
  the same as outside of the cell
• Under these conditions, water diffuses into and
  out of the cell at EQUAL RATES, so there is NO
  net movement of water
• Remains at equilibrium

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Hypertonic

• The concentration of solute molecules outside the
  cell is higher than the concentration of solutes
  inside the cell
• WATER DIFFUSES OUT OF THE CELL until Equilibrium
  is established

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Hypotonic

• The concentration of solute molecules outside the
  cell is lower than the concentration of solutes
  inside the cell
• WATER DIFFUSES INTO THE CELL until Equilibrium is
  established

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Facilitated Diffusion

• Most molecules cannot cross the cell membrane by
  simple diffusion
• Some Molecules are CARRIED across by CARRIER
  PROTEINS EMBEDDED IN the Cell Membrane
• Requires NO energy

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• Carrier Proteins CHANGE SHAPE when Molecules
  ATTACH to them
• The Change in Shape of the Carrier Protein
  ENABLES the Molecule to CROSS the Membrane.
• The use of carrier proteins is called facilitated
  diffusion.

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Active Transport

• In many cases, cells must move materials from an
  area of low concentration to high concentration
• This requires energy
• When energy is used to transport molecule across
  a membrane, this is called active transport

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• Small molecules and ions are carried across
  membranes by proteins in the membrane that act
  like pumps
• Large molecules need to be transported in Bulk
• Bulk transports include endocytosis, and
  exocytosis

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Endocytosis

• During ENDOCYTOSIS the Cell Membrane  folds into
  a POUCH that encloses the Particles.
• The Pouch pinches off INSIDE the Cell to form a
  VESICLE (membrane-wrapped bubbles).
• The VESICLE can then fuse with other Organelles
  or release its contents into the cytoplasm

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Pinocytosis and Phagocytosis

• Two forms of Endocytosis
• Pinocytosis is often referred to as cell
  drinking
• Bring in fluids and solutes
• Phagocytosis is often referred to as cell
  eating
• Brings in food or other cells

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Exocytosis

• The opposite of endocytosis
• Gets rid of wastes