Transcript
Chapter 5Chapter 5Life’s Border: The Plasma MembraneLife’s Border: The Plasma Membrane
The Plasma MembraneThe Plasma Membrane
– All cells have a plasma membrane that serves as the interface between the cell and the world outside it• defines the outer boundary of each cell • selectively permeable• Made up of 4 components (pg. 92):
–Phosopholipid bilayer–Cholesterol (structural support)–Proteins–Glycocalyx (carbohydrate chains)
The Plasma MembraneThe Plasma Membrane
Plasma Membrane StructurePlasma Membrane Structure
– Composed of a phospholipid bilayer – Fluid mosaic model (pg. 95)
• Proteins are embedded in this double lipid layer and give the membrane its mosaic character.
Phospholipid BilayerPhospholipid Bilayer
Roles of Membrane ProteinsRoles of Membrane Proteins
Transport Across MembranesTransport Across Membranes• The plasma membrane regulates the passage of
molecules into and out of the cell• Two types:
– Passive transport• No energy required• Move down a concentration gradient
– Active transport• Energy required• Move against a concentration gradient
Passive Transport: DiffusionPassive Transport: Diffusion
• Diffusion is the net movement of solute molecules down a concentration gradient (pg. 96)– movement is from high to low
concentration– continues until an equilibrium is
reached– a drop of dye in water illustrates
diffusion
Diffusion of LiquidsDiffusion of Liquids
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Facilitated Diffusion: Help from ProteinsFacilitated Diffusion: Help from Proteins
• No energy is required
• Passive transport of materials through the plasma membrane that is aided by a transport protein (pg. 99)
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Diffusion through Membranes: OsmosisDiffusion through Membranes: Osmosis
– Osmosis is the passive transport of water across a selectively permeable membrane • From a high water concentration (low solute) to a
low water (high solute) concentration• Cells will gain or lose water relative to their
surroundings–pg. 96 - 98
Cell in Cell in IsotonicIsotonic Solution Solution
CELLCELL
20% NaCL80% H2O
20% NaCL
80% H2O
The cell is at _______________.equilibrium
ENVIRONMENTENVIRONMENT
NO NET NO NET MOVEMENMOVEMENTT
Cell in Cell in HypOtonicHypOtonic Solution Solution
(hypo = less than)
CELLCELL
10% NaCL90% H2O
20% NaCL
80% H2O
What is the direction of water movement?
Water moves in and cell swells
Cell in Cell in HypertonicHypertonic Solution Solution
(hyper = more than)
CELLCELL
30% NaCL70% H2O
20% NaCL
80% H2O
What is the direction of water movement?
ENVIRONMENTENVIRONMENT
Water moves out and cell shrinks
Osmosis & Cell EnvironmentsOsmosis & Cell Environments
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Active TransportActive Transport
• During active transport cells use energy to move substances against a concentration gradient.– pg. 99
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Bulk Transport (pg. 101)Bulk Transport (pg. 101)– Exocytosis
• Secretes substances outside of the cell.
Bulk TransportBulk Transport– Endocytosis
• Takes material into the cell.–Pinocytosis = “cell drinking”–Phagocytosis = “cell eating”
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Diffusion
Requires no energy
Passive transport
Higher solute concentration
Facilitateddiffusion
OsmosisHigher water
concentration
Higher soluteconcentration
Requires energy
Active transport
Solute
Water
Lower soluteconcentration
Lower waterconcentration
Lower soluteconcentration
Fig 5.7 pg. 99
Chapter 5 Review• What are the main functions of the plasma membrane?• What 4 components make up the plasma membrane?
– pg. 92-95 Fig 5.1• What is meant by the fluid mosaic model? (pg. 95)• Distinguish between passive and active transport. • What are the 3 examples of passive transport?
– pg. 99 Fig 5.7
• Distinguish between diffusion and osmosis (pg. 96-98)• Distinguish between endocytosis & exocytosis (p.101)• Distinguish between pinocytosis & phagocytosis
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