Cellular Transport

How Molecules Are Transported Across The Cell Membrane.

Essential Questions• How do cells maintain homeostasis?• How are cell membranes (plasma

membranes) selectively permeable (semi-permeable)?

• Why is it important that cells are able to transport molecules with (active transport) and without (passive transport) energy?

Passive Transport• Cell uses no energy • Random movement of particles

along a concentration gradient from an area of high concentration to an area of low concentration.

– (HighLow)• Concentration gradient -

difference in the concentration of substance from one area to another.

• Three types:

3 Types of Passive Transport

1. Diffusion2. Facilitative Diffusion3. Osmosis

1. Diffusion• Diffusion: -random

movement of particles from an area of high concentration to an area of low concentration.

– continues until all molecules are evenly spaced or at equilibrium (equal)

Simple Diffusion Animation

• Facilitated diffusion: diffusion of specific particles along concentration gradient (High Low) with help proteins in membrane. a.Carrier Proteins -bind to

specific molecules to carry across membrane.a.Transport large particles

that can’t pass through on own. Ex. Glucose

b.Ion Channels Protein - transports ions (charged particles) through a polar pore.a.Ex. Na+, K+, Cl-

Facilitated

diffusion (Channel Protein)

Diffusion

(Lipid Bilayer

)

: 2. Facilitated

Diffusion

Carrier Protein

A B

• http://bio.winona.edu/berg/Free.htm

High Concentration

Low Concentration

Cell Membrane

Glucosemolecules

Proteinchannel

Facilitated Diffusion

Go to Section:

Transport ProteinThrough a

Cellular Transport From a- HigHig

hh

LowLow

• Channel Proteins animations

• Osmosis: diffusion of water through a selectively permeable membrane– Moves from a high

concentration of water to a low concentration of water

• Cell cannot control movement of water through cell membrane as water too small and in such abundance.

Osmosis animation 3. Osmosis

Effects of Osmosis on Life• Water moves freely through

pores.• Substances dissolve well in water.

– Solute: what is being dissolved– Solvent: what dissolves the

solute• In salt water, the solute is the salt

and the solvent is the water• Cells can be placed in 3 kinds

of water solutions that affect their homeostasis.

Hypotonic Solution

Hypotonic: Solution has a lower concentration of solutes and a higher

concentration of water than inside the cell. (Low solute; High water)

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

( called lyse)!

• Osmosis Animations for

isotonic, hypertonic, and

hypotonic solutions

Hypertonic Solution

Hypertonic: Solution has a higher concentration of solutes and a lower

concentration of water than inside the cell. (High solute; Low water)

Result: Water moves out of the cell into the solution: Cell shrivels or

shrinks!

• Osmosis Animations for

isotonic, hypertonic, and

hypotonic solutions

shrinks

Isotonic SolutionIsotonic: Concentration of solutes in the solution is equal to the concentration of

solutes inside the cell.

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

(Dynamic Equilibrium)

• Osmosis Animations for

isotonic, hypertonic, and

hypotonic solutions

In what type of solution are these cells?

A CB

Hypertonic

Isotonic

Hypotonic

Real Life Examples

If you are stranded in the ocean, should you drink the water to stay alive?

Why do we wrinkle when we are in the tube too long?

Why does it help to gargle salt water when we have a

sore throat?

What happens to a snail when you put salt water on

it?