Transport Across the Cell Membrane

Types of Cellular Transport

• Passive Transport

cell doesn’t use energy1. Diffusion

2. Facilitated Diffusion

3. Osmosis

• Active Transport

cell does use energy1. Protein Pumps

2. Endocytosis

3. Exocytosis

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DIFFUSION

• Food, water, and other substances are made of different kinds of particles, such as molecules and ions.

Particles are always moving, like dancers on a crowded dance floor.

Solutions are made of 2 parts:

• Solute: Substance that is dissolved

• Solvent: Liquid (solute) it is dissolved in

• You can tell how particles will tend to move if you know how crowded they are.

• Concentration refers to how crowded particles are.

A juice concentrate is a very strong form of juice. It has many more juice particles than regular juice does.

• In a concentrate, the juice particles are very crowded.

When you mix the concentrate with water, the juice particles spread out in the water.

•They tend to move away from places where they are concentrated

Thus, the particles become less concentrated.

Particles will continue to move from areas of high concentration to areas of low concentration until they reach equilibrium.

•This process is called diffusion.

What is a Concentration Gradient?

• Concentration gradient: the difference in concentration of molecules in physical space

• Particles move down their concentration gradient in diffusion

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• Watch the demonstration with food coloring in water, then answer the following:

Explain why the dye spreads out in the water. Use the words concentration and diffusion in your answer.

Diffusion Through a Cell Membrane• Cells also need food

and water to live

• Substances move into and out of the cell through its cell membrane

• A cell membrane is like the cell’s skin.

•Just as ink diffuses in water, some substances can diffuse into and out of a cell through its cell membrane.

Which molecules will diffuse in each of the figures below?

1 2 3 4

5 6

ANSWERS1 2 3 4

5 6

No Movement

No Movement

Reviewing Vocabulary1. Some substances move into and out of cells

by diffusion.2. The word concentration refers to how

crowded particles are.3. Some particles diffuse into and out of cells

through the cell membrane4. Particles tend to move toward places where

they have a low concentration.5. Particles tend to move away from places

where they have a high concentration6. Give one example of diffusion in your home.

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OSMOSIS• Most of your body

is made of water.

• This water can move into and out of your cells

• Water can enter and leave your cells by diffusion.

When water DIFFUSES through a CELL MEMBRANE, the process is called OSMOSIS.

In the picture, water is diffusing through a cell membrane.

Why is the water moving INTO the cell in the picture?

Water particles

Outside of Cell

Inside of Cell

Cell Membrane

• Because water has a lower concentration inside the cell than outside the cell.

• Water moves into the cell by OSMOSIS.

• What happens to the raisin after sitting in the water for a while?

It becomes largerWhy does this happen?

• Water molecules have a lower concentration inside the raisin. Outside the raisin, water molecules are crowded. Water molecules diffuse into the raisin by osmosis.

• Cells do not use energy to move particles by osmosis or diffusion

• Particles move freely into and out of cells. This kind of movement is called PASSIVE TRANSPORT

Complete the Vocabulary Review.

PASSIVE TRANSPORT

Diffusion, Osmosis and facillitated diffusion are all types of passive transport

2. Facilitated diffusion: diffusion of specific particles through 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

Facilitated diffusion (Channel Protein)

Diffusion (Lipid

Bilayer)

Passive Transport: Facilitated Diffusion

Carrier Protein

A B

• http://bio.winona.edu/berg/Free.htm

High Concentration

Low Concentration

Cell Membrane

Glucosemolecules

Proteinchannel

Passive Transport: Facilitated Diffusion

Go to Section:

Transport Protein

Through a

Cellular Transport From a-High

Low

Vocabulary Review1. One example of osmosis is water diffusing into a

raisin.2. Cells do not work to move molecules by passive

transport.3. Two forms of passive transport are osmosis and

diffusion.4. In diffusion and osmosis, particles move by

themselves.5. Water molecules tend to move to places where they

have a low concentration.6. Give one way that osmosis is similar to diffusion.

Both move from high to low concentration.

STOP!

• My brain is exploding!!!!

Active vs. Passive Transport

• Passive Transport – does not require energy. Particles move from high to low concentration.

• Active Transport – does require energy because molecules are moving from low to high concentration

Types of Cellular Transport

• Passive Transport

cell doesn’t use energy1. Diffusion

2. Facilitated Diffusion

3. Osmosis

• Active Transport

cell does use energy1. Protein Pumps

2. Endocytosis

3. Exocytosis

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be hard work!!

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•Animations of Active Transport & Passive

Transport

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 (against a concentration gradient)

•(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!

Let’s Watch a Video!

• https://www.youtube.com/watch?v=dPKvHrD1eS4

• Refer to your video worksheet and answer questions as you listen and watch

Endocytosis• Some things the

cells needs are too large to pass through the cell membrane.

• The cell membrane can surround a large particle located outside the cell.

The membrane forms a sac around the particle.

Then the sac opens inside the cell.

• The sac moves to the membrane and then opens outside the cell.

• Waste particle move OUTSIDE the cell.

• This process of moving large particles OUT of the membrane is called EXOCYTOSIS.

Large particle leave the cell in sacs too.

Inside a cell, a sac forms around large waste

particles.

Exocytosis

Cells Maintain Balance• The cell controls its food and water content

by moving ions, molecules, and larger particles into or out of itself. This is how the cell maintains homeostasis.

• Homeostasis Simulation

http://trc.ucdavis.edu/biosci10v/bis10v/media/ch17/hot_guy.html

• Complete the Vocabulary Review

Vocabulary Review

1. Cells use energy to move molecules by active transport.

2. Diffusion and osmosis are two kinds of passive transport.

3. Some molecules are too large to pass through the cell membrane.

4. Cells take in large molecules by endocytosis.

5. Cells must maintain a balance, called homeostasis.