Chapter 7.3 The Cell Membrane; Active & Passive Transport

Diffusion• Molecules tend to “spread out”• Move from an area of high concentration to

low concentration• Requires no energy

Diffusion= The movement of molecules from an area

of high concentration to an area of low concentration

Equilibrium

What’s this have to do with cells? Think about it…cells are like a nation

• Cells need things like a nation needs things…– Exports, imports– Has borders

• Why may a cell need materials to leave or enter a cell?

• How might this occur?

Cell Membrane Function:the GATEKEEPER

1)

2)

3)

Cell Membrane StructureCharacteristics:

Cell Wall• Found in most prokaryotes and some

eukaryotes (plants, fungi, algae)• Main function is support

Types of Cellular Transport

• Passive Transport cell doesn’t use energy

1. Diffusion2. Facilitated Diffusion3. Osmosis

• Active Transportcell does use energy

1. Protein Pumps2. Endocytosis3. Exocytosis

high

low

This is gonna be

hard work!!

high

low

Weeee!!!

•Animations of Active Transport & Passive

Transport

Passive Transport• cell uses no energy • molecules move randomly• Molecules spread out from an area of high

concentration to an area of low concentration.

• (HighLow)• Three types:

3 Types of Passive Transport

1. Diffusion 2. Facilitated Diffusion – diffusion with the

help of transport proteins 3. Osmosis – diffusion of water

Lesson OverviewLesson Overview Cell TransportCell Transport

Diffusion

In a cell:- cytoplasm a solution of many different substances dissolved in water.

As you know: -In any solution, solute particles tend to move from an

area where they are more concentrated to an area where they are less concentrated.= Diffusion

Diffusion---- the driving force behind the movement of many substances across the cell membrane.

Passive Transport: 1. Diffusion

1. Diffusion: random movement of particles from an area of ______ concentration to an area of _______ concentration.

(__________________)• Diffusion continues until all

molecules are evenly spaced (equilibrium is reached)-

• Note: molecules will still move around but stay spread out.

http://bio.winona.edu/berg/Free.htm

Simple Diffusion Animation

7-15 diagram pg 209

• Discuss with a friend and DRAW: What would be different in 7-15 if the high concentration of solutes had been inside the cell to start with?

2. Facilitated diffusion: diffusion of specific particles through transport proteins(protein channels/carriers) found in the membrane a. Transport Proteins are

specific – they “select” only certain molecules to cross the membrane

b.Transports larger or charged molecules

Facilitated diffusion (Channel Protein)

Diffusion (Lipid

Bilayer)

Passive Transport: 2. Facilitated Diffusion

Carrier Protein

A B

• http://bio.winona.edu/berg/Free.htm

High Concentration

to a Low Concentration

Cell Membrane

Glucosemolecules

Proteinchannel

Passive Transport: 2. Facilitated Diffusion

Go to Section:

Transport Protein

Through a

Cellular Transport from aHigh

Low

• Channel Proteins animations

Lesson OverviewLesson Overview Cell TransportCell Transport

Osmosis: A Type of Facilitated Diffusion

• Inside of a cell’s lipid bilayer is hydrophobic—or “water-hating.”

• water has a hard time getting through.

• Water channel proteins, known as ______________________ allow water to pass right through them.

This movement of water is an extremely important biological =

• 3.Osmosis: diffusion of water through a selectively permeable membrane

• Water moves from high to low concentrations •Water moves freely

through pores.

•Solute (green) too large to move across.

Osmosis animationPassive Transport: 3. Osmosis

Rule for Osmosis:

Water will get sucked to wherever there is a higher concentration of salt.

Osmosis

= The diffusion of water across a selectively permeable membrane

ONLY THE WATER is moving.

Lesson OverviewLesson Overview Cell TransportCell Transport

How Osmosis Works

Barrier below is permeable to water but not to sugar. -water molecules can pass through the solute, sugar, cannot.

Lesson OverviewLesson Overview Cell TransportCell Transport

How Osmosis Works • More sugar molecules on the

• The concentration of water is __________________________ where more of the solution is made of sugar.

Lesson OverviewLesson Overview Cell TransportCell Transport

How Osmosis Works There is a net movement of water into the compartment containing the concentrated sugar solution.

Water will tend to move across the barrier until equilibrium is reached. At that point, the concentrations of water and sugar will be the same on both sides.

Lesson OverviewLesson Overview Cell TransportCell Transport

How Osmosis Works

When the concentration is the same on both sides of the membrane, the two solutions will be ______________ which means “same strength.”

Lesson OverviewLesson Overview Cell TransportCell Transport

Osmotic Pressure

The net movement of water out of or into a cell produces a force known as osmotic pressure.

= the force created by the net movement of water through a cell membrane.

Isotonic Solution iso=sameIsotonic: The concentration of solutes in the solution is __________________ concentration of solutes inside the cell.

Result: Water moves equally in both directions and the cell remains same size!

Isotonic

Hypotonic Solution Hypo=less

Hypotonic: The solution has a _______ concentration of solutes and a __________ concentration of water than inside the cell. (_______solute; _______water)

Result: Water moves from the solution to inside the cell: Cell Swells and bursts open

Hypotonic

Hypertonic Solution hyper = more

Hypertonic: The solution has a ________ concentration of solutes and a ________ concentration of water than inside the cell. (_______ solute; ________ water)

Result: Water moves from inside the cell into the solution: Cell shrinks

shrinks

Hypertonic

What type of solution are these cells in?

A CB

Hypertonic Isotonic Hypotonic

How Organisms Deal with Osmotic Pressure

• Paramecium (protist) removing excess water video

•Bacteria and plants have cell walls that prevent them from over-expanding. Pressure can damage the cell wall though.

•A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from over-expanding.

•Salt water fish pump salt out of their specialized gills so they do not dehydrate.

•Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.

Passive Transport Review

• Requires no energy

• Diffusion

• Osmosis = Diffusion of water

• Facilitated Diffusion: carrier proteins “help” molecules across the membrane like a tunnel

Active Transport•cell uses energy

•actively moves molecules to where they are needed

•Movement from an area of low concentration to an area of high concentration

•(Low High)

•Three Types:

Types of Active Transport

1.Protein Pumps –

•Example: Sodium / Potassium Pumps are important in nerve responses.

Sodium Potassium Pumps (Active Transport using proteins)

Protein changes shape to move molecules: this requires energy!

Lesson OverviewLesson Overview Cell TransportCell Transport

Active Transport

• Small molecules pumped into or out of cell by transport proteins on the cell membrane.

• Transport goes against a concentration gradient

• Requires cellular energy (ATP)

Types of Active Transport

• 2. _________________: taking bulky material into a cell • Uses energy• Cell membrane in-folds

around food particle• “cell eating”• forms food vacuole &

digests food• This is how white blood

cells eat bacteria!

Types of Active Transport

3. __________________Forces material out of cell in bulk• membrane surrounding the

material fuses with cell membrane

• Cell changes shape – requires energy

• EX: Hormones or wastes released from cell

Endocytosis & Exocytosis animations

Lesson OverviewLesson Overview Cell TransportCell Transport

Molecular Transport

A considerable portion of the energy used by cells in their daily activities is devoted to providing the energy to keep this form of active transport working.

The use of energy in these systems enables cells to concentrate substances in a particular location, even when the forces of diffusion might tend to move these substances in the opposite direction.

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