Movement through the Cell Membrane

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Movement through the Cell Membrane

• Biology
• Mrs. Volin

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Fluid-mosaic model of membrane structure
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The cell membrane isselectively permeable
Allows only selected substances to pass
through.
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Concentration of a solution

• Mass of a solute in a volume of solution
• Mass/volume
• g/L

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Diffusion
equilibrium
DIFFUSION - MOVEMENT OF MOLECULES FROM AN AREA OF
HIGH CONCENTRATION TO AN AREA OF LOW CONCENTRATION
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Diffusion

• Molecules move from an area of high concentration
  to an area of low concentration
• In other words, molecules move down their
  concentration gradient.

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Equilibrium

• When concentration is same throughout the solution

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Osmosis

• A special case of diffusion
• Diffusion of water across a selectively permeable
  membrane

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Osmosis
DIFFUSION OF WATER ACROSS A SELECTIVELY PERMEABLE
MEMBRANE
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Osmosis
WATER HIGHLY CONCENTRATED
WATER LESS CONCENTRATED
IN OSMOSIS, WATER MOVES FROM ITS AREA OF HIGH
CONCENTRATION TO ITS AREA OF LOW CONCENTRATION.
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Outside and inside are isotonic
Outside is hypotonic
Outside is hypertonic
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Red blood cells in an isotonic solution
normal red blood cells
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Red blood cells in a hypertonic solution
Red blood cells in a hypotonic solution
Crenation
Lysis
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Paramecium
Contractile vacuole
Contractile vacuole
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Osmosis in plant cells
Cell is flaccid.
Cell is turgid.
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Passive Transport vs. Active Transport

• Diffusion and osmosis occur without need for
  energy. Molecules move from areas of higher
  concentration to lower concentration --- they are
  forms of passive transport
• Facilitated diffusion is also a form of passive
  transport

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Membrane protein
Protein channel allows a specific substance to
cross, along its concentration gradient
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Passive Transport

• No energy is required from the cell
• Substances are moved along their
• concentration gradients
• Diffusion, osmosis, facilitated diffusion

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Active Transport

• Substances are moved against their concentration
  gradients
• Requires energy

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Active Transport
Active transport requires energy. Molecules are
moved against their concentration gradient.
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• Sodium-potassium pump
• Pumps Na out of cell
• Pumps K into cells
• Against concentration gradients
• Most animal cells have high K and low Na
• Requires energy, therefore it is active transport

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Endocytosis
A form of active transport
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2 Types of Endocytosis

• Phagocytosis (cellular eating)
• Pinocytosis (cellular drinking)

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• Phagocytosis by an amoeba

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Exocytosis
A form of active transport.
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Summary

• Passive transport Active transport
• Diffusion Na K pump
• Osmosis Endocytosis
• Facilitated diffusion Exocytosis