3.7 Passive Transport

8/14/2019 3.7 Passive Transport

1/15

!et s move!et s move3.7 Describe passive transport.


2/15

Phospholipid BilayerWho remembers what the function of the cell

membrane is?

It allows certain substances in and out of the

cell

If you remember, what types of membraneproteins allow substances to move in and outof the cell?

HINT: The proteins are made of both hydrophilicand hydrophobic amino acids

Transport Proteins!!


3/15

Phospholipid BilayerMany substances move in and out of the cell

membrane without the use of transportproteins

They do this through a process calledmolecular transport

Break it down Molecular + Transport

There are two different types of moleculartransport:

Passive Transport

Active Transport


4/15

Passive vs. Active

TransportPassive Transport Movement across the

cell membrane that does NOT require energy

Ex. Diffusion, Osmosis, Facilitated Diffusion

Active Transport Movement across the cellmembrane that DOES require energy

Ex. Sodium-Potassium Pump

What is the difference between an active andpassive person?


5/15

Passive Transport:

Thought ExperimentImagine there are 100 bouncing rubber balls in

my room

We open the door to the prep room

What is going to happen?


6/15

Passive TransportThis is exactly how passive transport works,

except that the door we opened is really theselectively permeable cell membrane

A substance wants to reach equilibrium

What word is in equilibrium?

Equilibrium the concentration of a substanceis equal throughout a space

In our case, there is equal amounts of asubstance inside and outside of a cell


7/15

Concentration GradientIn order for this to reach equilibrium, what has

to happen?

The substance must move from a higherconcentration, where there is more, to a

lower concentration where there is lessConcentration Gradient A difference in the

concentration of a substance across a space


8/15

See-Saw DiagramA substance is said to move DOWN its

concentration gradient when its reachingequilibrium

Note: This has nothing to do with the actualdirection that the molecules are moving

You can represent a concentration gradientwith a see-saw diagram

Lets draw one together to show howsubstances move down


9/15

-S e e S a w D ia g ra m20 H20

2 H20

2 H20

20 H20

11 H2011 H20


10/15

DiffusionDiffusion Movement of a substance from

higher concentration to lower concentrationcaused by the random movement of particles

This eventually leads to equilibrium

Now well do a demonstration with water andfood coloring


11/15

DiffusionMany molecules and ions that are dissolved in

the cytoplasm move in and out of the cell bydiffusion

Why would a substance diffuse out of a cell?

There is a higher concentration inside the cell

Why would a substance diffuse in to a cell?

There is a higher concentration outside thecell

The process of diffusion across the cellmembrane can only occur for very small ornon-polar molecules


12/15

OsmosisOsmosis is the diffusion of water through a

selectively permeable membrane

How do molecules move in diffusion?

From a higher concentration to a lowerconcentration

Down its concentration gradient (see-saw)

This means that osmosis is a form of passivetransport


13/15

Osmosis

Osmosis can get trickyIts not really a measure of how many water

molecules are inside or outside of a cell

We are more interested in the other substances

(like salt) that aredissolved

in the water.If there is a high concentration of salt, then there

is a low concentration of water.

If there is an area with a low concentration of salt

its because there is a high concentration ofwater.

So the water will diffuse from the highconcentration of water (with low amounts of

salt) to the low concentration of water (withhigh amounts of salt).


14/15

Osmosis: Key PointsIts all about the diffusion of FREE water

molecules from a higher concentration to alower concentration

More substances being dissolved means lessfree water molecules a lower concentrationof free water

So water moves from a low concentration of

dissolved substances to a high concentrationof dissolved substances

Osmosis is a form of passive transport anddoes not require energy


15/15

ith a partnerith a partnernswer thenswer theuestions at theuestions at the .nd of your notes.nd of your notes

Documents

3.7 Passive Transport