Transport Across

the Membrane the Membrane (6.3)(6.3)

Move it!Move it!• Materials such as water, nutrients, dissolved

gases, ions, and wastes must constantlyconstantly move in two-way traffictwo-way traffic across a cell's plasma membrane.

• Cellular membranes function like Cellular membranes function like gatekeepersgatekeepers, – letting some molecules through but not others. – while certain molecules pass freely through the

"gates," others move only when the cell cell expends energyexpends energy

Crossing the Crossing the BorderBorder1. Passive Transport

– (no NRG required)– High Concentrations to LowHigh Concentrations to Low

• Diffusion• Facilitated Diffusion• Osmosis

2. Active Transport – (NRG required)– Low Concentrations to High Low Concentrations to High

Passive Passive TransportTransport–No energy useNo energy use

–RandomRandom motion and concentrations Difference in concentration of a substance = the the

concentration gradientconcentration gradient– If a solution is in “ “Equilibrium”… Equilibrium”…

• concentrations are equalequal

– The movement of substances from: “high concentrations to low concentrations” It is

called: “ “Down the concentration gradient”Down the concentration gradient”

Slide O’ ScienceNo NRG Needed

here brah’

Down The Gradient

The The

Passive

Passive

Transpor

Transpor

ttHigh High

ConcentraConcentrationtion

Low Low ConcentraConcentra

tiontion

Examples of Diffusion

• Food coloringFood coloring – Will gradually move through uncolored water…– WHY?

• Concentrations WANT to be in equilibrium • Water turns a light blue

• Air FreshenerAir Freshener– Will gradually spread to all – WHY?

• Concentrations WANT to be in equilibrium• Is why scent is strong at first and then gets weaker

Diffusion in Picture

Osmosis•A type of Passive Transport

(Diffusion)

–Specifically the diffusion of water–3 Ways this can occur

• #1 Water diffuses out of cell– Hypertonic solution Hypertonic solution

• #2 Water diffuses into a cell– Hypotonic solutionHypotonic solution

• #3 No net movement of water– Isotonic solutionIsotonic solution

Hypertonic solutionsolution

Water

If there is a If there is a high high

concentration of concentration of

solutesolute there there

must then bemust then be a a

LOW LOW concentration of concentration of

water!!water!!

Hyper = more Hyper = more

solutesolute

HypHypoo = more = more

H2H2OO

What is the What is the

direction of the direction of the

flow of water?flow of water?

Hypootonic solution

Water

Isotonic Solution

Quick Review

• A hypertonic cell would have a higher concentration of solute than the solution it is in?– Yes, hyper = more solute

• In a hypotonic solution, the movement of water is into the cell? (True or False?)– Water moves from High to Low

• HYPO = More H2O, • TRUEwater moves INTO the cell

The Crossing Guards of the Membrane

Transport Proteins!!Transport Proteins!!

•channels” allow those substances to cross that cannot on their own :

•Ion Channels allow K+ and Na- to cross into cell

•Some channels always open

•some open in response to stimulus

•Still no use of energy!Still no use of energy!

Why? Hydrophobic

Area

Facilitate

d Diffusion

Facilitated Diffusion

• Carrier proteins transport substances “down their concentration gradient”– Move down gradient with NO energy use

Review

• What are the 3 types of passive transport

• What are the 3 ways water can move across a membrane? (osmosis)

• Does passive transport move up or down the concentration gradient?

ACTIVE TRANSPORTACTIVE TRANSPORT• Requires NRG to be

used by the cell… Why?– UP the UP the

concentration concentration gradient gradient

– specific transport protein pumps opposite direction of diffusion

– requires chemical energy supplied primarily by the mitochondria!

– How your nerve cells work!

NRG

Slide O’ Science

Phew! This

takes too much WORK

UP The GradientUP The Gradient

The The

Active

Active

Transpor

Transpor

tt

High High ConcentraConcentra

tiontion

Low Low ConcentraConcentra

tiontion

Exit Ticket

• What are the 2 types of transport across the membrane called?

• What are the types of Passive transport?• Contrast Passive transport and Active

Transport.• Where does the NRG come from for Active

Transport?• Which direction on the concentration

gradient does active and passive transport move?