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Cell TransportCell Transport

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Check Your Understanding

At the end of today’s lesson, you should be able to

answer the following questions:

• What are the parts of the cell membrane and what do they do?

• What is the “Fluid Mosaic Model?”• Describe the processes of diffusion, osmosis,

facilitated diffusion, and active transport.

Cell Membrane

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Regulates passage of materials into and out of the cell

Parts of the membrane:

A) lipid bilayer (2 layers)B) proteinsC) cholesterolD) carbohydrate chains

Lipid Bilayer• Made of 2 sheets of

phospholipids, a type of lipid with a head and 2 tails

• Hydrophilic (water loving) head

• Hydrophobic (water fearing) tail

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Why do the phospholipids arrange themselves in a bilayer?

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• Membrane Proteins: Act as channels for large particles to enter and leave the cell

• Fluid-Mosaic Model: describes the flexibility of the lipid bilayer with a mosaic of proteins and other molecules

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Carbohydrate Chains

• Recognize parts of molecules to determine what molecules can be brought into the cell

• Can be attached to proteins or phospholipids

• Lock and Key Fit!

Label the Parts of the Membrane!• Outside cell• Inside cell• Phospholipid • Protein• Carbohydrate Chain

Function of the Cell Membrane

• Regulates what enters and leaves the cell

• Provides protection and support

Random Transition…AHHHH!

• This may seem completely rando…but I promise the dots will connect later!

Concentration

• In a solution, the concentration is the mass of solute in a given volume of solution

• A difference in concentration over a distance is called a concentration gradient

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Simple DiffusionSimple Diffusion

• Description: Molecules move from area of HIGH to LOWHIGH to LOW concentration

• This means they are going DOWN the CONCENTRATION GRADIENT

• PASSIVE Process (no energy required)

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Simple Diffusion of a Solute Across a Membrane

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Can all solutes cross the membrane by simple

diffusion?• NO!

• The membrane is selectively permeable, this means only certain solutes (typically small ones) can pass across by simple diffusion

• The solution? – Channel Proteins!

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Facilitated Diffusion• Description: Diffusion of certain molecules

through a selectively permeable membrane, made possible by protein channels

• PASSIVE Process• DOWN gradient

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OsmosisOsmosis• Description: Diffusion of WATER across a selectively

permeable membrane

• PASSIVE process

• DOWN GRADIENT (that is, WATER moves down its gradient)

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Cell in Isotonic SolutionCell in Isotonic Solution

CELLCELL

10% solute

90% water

10% solute90% water

What is the direction of water movement?

The cell is at EQUILIBRIUM.

ENVIRONMENTENVIRONMENT

Solution outside the cell has the SAME solute (and water) concentration as the cell itself

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Cell in Hypotonic SolutionCell in Hypotonic Solution

CELLCELL

10% solute

90% water

20% solute80%

water

What is the direction of water movement?

ENVIRONMENTENVIRONMENT Solution outside the cell has a LOWER solute (HIGHER water) concentration than the cell itself

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Cell in Hypertonic SolutionCell in Hypertonic Solution

CELLCELL

15% solute

85% water

5% solute95%

water

What is the direction of water movement?

ENVIRONMENTENVIRONMENT Solution outside the cell has a HIGHER solute (LOWER water) concentration than the cell itself

Isotonic Solution

NO NET MOVEMENT OF

H2O (equal amounts entering & leaving)

Hypotonic Solution

Cell Bursting

Hypertonic Solution

Cell Shrinking..\..\..\Downloaded Videos\Onion Cells Plasmolysis.avi

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Osmosis in Red Blood CellsOsmosis in Red Blood Cells

IsotonicIsotonic Hypotonic Hypertoniccopyright cmassengale

Osmosis in Plant Cells

Active Transport

• Description: Movement of materials from LOW to HIGH concentration

• ACTIVE process (uses energy)

• UP Concentration Gradient

Active TransportMolecular Pumps

ATP

Molecular pumps are membrane proteins that use energy from ATP to move molecules across cell membranes. (Each pump moves one type of molecule)

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Endocytosis vs. Exocytosis

• Endocytosis: taking large amounts of material into the cell

• Exocytosis: sending large amounts of material out of the cell

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Endocytosis:Phagocytosis & Pinocytosis

Phagocytosis: The membrane folds to enclose solid particle (cell eating)

Pinocytosis: The membrane folds to enclose liquid with dissolved materials (cell drinking)

• In endocytosis, the membrane pinches in to form a vesicle

• The vesicle may later join with a lysosome so that particles can be “digested”

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Vesicles

Exocytosis1

Products of the ER are packaged in vesicles at the Golgi and released at the cell membrane.

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Cell Membrane and Homeostasis

• Refresher from Characteristics of Life…what is homeostasis?

• How does the cell membrane help organisms to maintain homeostasis?