Types of Transport Across Cell Membranes 1. Passive Transport.
Passive Transport Where are membranes found? Cell Organelles.
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Transcript of Passive Transport Where are membranes found? Cell Organelles.
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Passive Transport
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Where are membranes found?
• Cell• Organelles
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Cell Membrane
• Allows certain things to enter and leave
• Phosphate head• Lipid tail
• Two layers
a.k.a. semipermeable phospholipid bilayer
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High Concentration Low Concentration
Concentration– amount of substance in
a given volume
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Passive
Passive Transport
•Movement of materials that DOES NOT require energy (ATP)
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Passive
Passive Transport
Diffusion
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Pas
sive
Tran
sport
High Concentration
Low Concentration
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Diffusion
• Move from HIGH to LOW concentration– “passive transport”– no energy needed
diffusion osmosis
movement of water
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Diffusion across cell membrane
• Cell membrane is the boundary between inside & outside…– separates cell from its environment
IN: foodcarbohydratessugars, proteinsamino acidslipidssalts, O2, H2O
OUT: wasteammoniasaltsCO2
H2O products
IN
OUT
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Diffusion• Continues until an equilibrium is
reached– Equilibrium – balanced; equally
distributed
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• What will happen when dye is added to a beaker of water?
a
b
c
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What causes diffusion?
• Movement of molecules– As they move they bump into each
other
• Collisions cause molecules to move away from each other
– http://www.stolaf.edu/people/giannini/flashanimat/transport/diffusion.swf
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Factors Affecting Diffusion
•Temperature—the higher the temperature, the faster diffusion occurs
•Molecular Size—the bigger the molecule, the longer diffusion takes
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Osmosis
Passive
Passive Transport
Diffusion
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Osmosis
• Diffusion of water across a selectively permeable membrane.
• Occurs until concentration is balanced on both sides of the membrane.
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Osmosis is diffusion of water
• Direction of osmosis is determined by comparing total solute concentrations– Hypertonic - more
solute, less water
– Hypotonic - less solute, more water
– Isotonic - equal solute, equal water
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Hypertonic
• Medium has more solute than the cell
• More water leaves the cell than enters it
• Cell will shrink
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Hypotonic
• The medium has less solute than the cell
• More water enters the cell
• The cell will swell
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Isotonic• Medium is exactly
the same solute concentration as the cell
• Amount of water moving in equals water going out
• The cell will stay the same size
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What is happening here?
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Osmosis
Passive
Passive Transport
Diffusion
Facilitated Diffusion
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Isnt the membrane “semi-permeable”?
• What molecules can get through directly?– fats & other lipids
inside cell
outside cell
lipid
salt
aa H2Osugar
NH3
What molecules can NOT get through directly?
polar molecules
H2O ions
salts, ammonia large molecules
starches, proteins
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Channels through cell membrane
• Membrane becomes semi-permeable with protein channels – specific channels allow specific
material across cell membrane
inside cell
outside cell
sugaraaH2O
saltNH3
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Facilitated Diffusion
• Diffusion through protein channels– channels move specific molecules across
cell membrane– no energy needed
“The Bouncer”“The Bouncer”
open channel = fast transport
facilitated = with help
high
low
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Active Transport• Cells may need to move molecules against
concentration gradient– shape change transports solute from
one side of membrane to other – protein “pump”– “costs” energy = ATP
ATP
low
high
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Active Transport
ATP ATP
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How about large molecules?
• Exocytosis– Through
vesicles & vacuoles
– “Exit Cell”
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Endocytosis
• Endocytosis– phagocytosis
= “cellular eating”
– pinocytosis = “cellular drinking
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Review
?
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Review
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Getting through cell membrane
• Passive Transport– Simple diffusion
• diffusion of nonpolar, hydrophobic molecules– lipids– high low concentration gradient
– Facilitated diffusion• diffusion of polar, hydrophilic molecules• through a protein channel
– high low concentration gradient
• Active transport– diffusion against concentration gradient
• low high
– uses a protein pump– requires ATP
ATP
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Transport summarysimplediffusion
facilitateddiffusion
activetransport
ATP
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Any Questions??