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