Download Sect 07.4

Section 07.4
Cellular Transport
Objectives
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Explain the processes of diffusion, facilitated diffusion, and active transport.
Predict the effect of a hypotonic, hypertonic, or isotonic solution on a cell.
Discuss how large particles enter and exit cells.
Main Idea
• Cellular transport moves substances within the cell and moves substances into and out
of the cell.
Diffusion
• Passive transport
◦ = movement of particles across the cell membrane without using energy
◦ three modes
 diffusion
 facilitated diffusion
 osmosis
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Diffusion
◦ = net movement of particles from an area of high concentration
 to an area of low concentration
◦ is controlled by
 temperature
 pressure
 concentration
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Dynamic equilibrium
◦ reached when diffusion of material into the cell
 equals diffusion of material out of the cell
◦ molecules continue to move
 but overall concentration remains the same
Diffusion across PM
• Facilitated diffusion
◦ = movement of materials across the plasma membrane using proteins
 uses transport proteins
◦ used to move
 other ions
 small molecules
◦ uses two types of transport proteins
 channel proteins
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carrier proteins
Channel proteins
◦ transport proteins that span the PM
 form a water-filled channel
◦ channel proteins
 opens and closes
• to allow substance to diffuse through the PM
Osmosis
• Osmosis
◦ = diffusion of water
 across a selectively permeable membrane
◦ regulation of osmosis
 an important factor in homeostasis w/in cell
◦ in cells
 water will move toward area of greater solute concentration
□ until dynamic equilibrium is reached
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Osmosis
◦ works together with solute/solvent conc
 solute dissolved in a solvent forms solution
□ water is the solvent in cells
 as conc of solution decreases
□ conc of solvent increases
◦ 3 types of solution concentrations
 isotonic
 hypotonic
 hypertonic
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Isotonic solution
◦ = when solute conc inside the cell
 equal to solute conc outside of cell
◦ meaning of isotonic
 iso□ Greek for equal
 -tonic
□ tension
◦ water still move thru PM
 but it enters at the same rate as it leaves
 no net movement of water
□ cell is in equilibrium with solution
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Hypotonic solution
◦ = when cell is in solution
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 that has a lower solute conc
net movement of water
 into the cell
causes cell to swell
in plant cells
 as cell swells
□ pm presses against cell
□ creating pressure called turgor pressure
□ plant becomes firmer
Hypertonic solution
◦ = when cell is in solution
 that has a higher solute conc
◦ net movement of water
 out of the cell
◦ causes cell to shrink
◦ in plant cells
 PM is pulled away from cell wall
Active transport
• Active transport
◦ = movement of substances
 across a PM
□ against a concentration gradient
 moves from an area of low concentration
□ to an area higher concentration
◦ requires the expenditure of energy
◦ uses carrier proteins
 commonly called pumps
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Sodium-Potassium ATPase pump
◦ carrier protein found in the membrane of animal cells
 acts as an enzyme
□ catalyzes the breakdown of ATP
◦ maintain the cellular level of Na+ and K+
 pump moves
□ 3 Na+ out of the cell
□ 2 K+ into the cell
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Endocytosis
◦ process of surrounding an object outside of the cell
 encloses it in a portion of the PM
 pinches it off forming a vesicle
□ with the object inside
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Two types of endocytosis
◦ phagocytosis
◦ pinocytosis
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Phagocytosis
◦ aka cellular eating
◦ process of taking solid material into the cell
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Pinocytosis
◦ aka cellular drinking
◦ process of taking liquids into the cell
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Exocytosis
◦ process of secreting materials at the PM
◦ opposite of endocytosis
 vesicle
□ migrates to PM
□ fuses to PM
□ dumps its contents to the outside of the cell