Cellular Transport

Notes

About Cell Membranes

• All cells have a cell membrane

• Functions:

a. Controls what enters and exits the cell to maintain an internal balance called homeostasis

b. Provides protection and support for the cell

TEM picture of a real

cell membrane.

What is the purpose of cellular transport?

• Homeostasis depends upon appropriate movement of materials across the cell membrane.

– Required materials must pass into the cells so they can be utilized.

• Ex. Oxygen and glucose for cellular respiration

– Waste materials must pass out of the cells as they are produced

• Ex. The CO2 produced as a waste product of cellular respiration

• The cell membrane regulates the passage of materials into and out of the cell.

– Needed materials move in

– Excess materials move out

How?

• Each individual cell exists in a fluid environment, and

the cytoplasm within the cell also has a fluid

environment. The presence of a liquid makes it

possible for substances (such as nutrients, oxygen,

and waste products) to move into and out of the cell.

• A cell membrane is semipermeable (selectively

permeable), meaning that some substances can pass

directly through the cell membrane while other

substances can not.

• Materials can enter or exit through the cell membrane

by passive transport or active transport.

Membrane

movement

animation

Types of Cellular Transport

• Passive Transport

cell doesn’t use energy

1. Diffusion

2. Facilitated Diffusion

3. Osmosis

• Active Transport

cell does use energy

1. Protein Pumps

2. Endocytosis

3. 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

• The random motion of molecules occurs

along the concentration gradient meaning

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 – is the spreading out of molecules

across a cell membrane until they are equally

concentrated.

2. Facilitative Diffusion – diffusion with the help

of transport proteins

3. Osmosis – diffusion of water

Passive Transport:

1. Diffusion

• Diffusion: random movement of particles from

an area of high concentration to an area of

low concentration.

• Diffusion continues until all molecules are evenly

spaced (equilibrium is reached)-Note: molecules will

still move around but stay spread out.

Simple Diffusion

Animation

• Facilitated diffusion: diffusion of specific particles along the concentration gradient (High Low) with the help of transport proteins found in the membrane

a. Transport Proteins are specific – they “select” only certain molecules to cross the membrane

b. Transports larger or charged molecules that cannot pass through the membrane on their own

c. Glucose is an example of a molecule that passes into the cell through facilitated diffusion

Facilitated

diffusion (Channel

Protein)

Simple

Diffusion

(Lipid

Bilayer)

Passive Transport:

2. Facilitated Diffusion

Carrier Protein

A B

• http://bio.winona.edu/berg/Free.htm

High Concentration

Low Concentration

Cell Membrane

Glucose molecules

Protein channel

Passive Transport: 2. Facilitated Diffusion

Go to

Section:

Transport

Protein Through a

Cellular Transport From a- High

Low

• Channel Proteins

animations

• Osmosis: diffusion of water

through a selectively permeable

membrane

• Water moves from a high

concentration of water to a low

concentration of water

• Because water is so small and in

such abundance, the cell

cannot control its movement

through the cell membrane.

Osmosis

animation

Passive Transport:

3. Osmosis

Effects of Osmosis on Life

• Water moves freely

through pores.

• Solute (green) too large

to move across.

• Reminder:

– Solute: what is being dissolved

– Solvent: what dissolves the solute

• In salt water, the solute is the salt and the solvent is the

water

Hypotonic Solution

Hypotonic: The 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 (lyse)!

• Osmosis Animations for isotonic,

hypertonic, and hypotonic solutions

Hypertonic Solution

Hypertonic: The 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!

• Osmosis Animations for isotonic,

hypertonic, and hypotonic solutions

shrinks

Isotonic Solution

Isotonic: The 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 C B

Hypertonic Isotonic Hypotonic

Active Transport

• Requires the cell to use energy

• Actively moves molecules to where they are

needed

• Molecules move against the concentration

gradient - from an area of low concentration

to an area of high concentration

• (Low High)

• Three Types:

Types of Active Transport

1. Protein Pumps -

transport proteins that

require energy to do work

• 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!

Types of Active Transport

• 2. Endocytosis: taking bulky

material into a cell by forming a vesicle

• 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. Exocytosis: 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