The Cell Membrane

What kinds of materials does a cell need to survive?

What kinds of materials does a cell need to survive?• Water

• Oxygen• Glucose (sugar)

• “Food”– Amino acids (from meat protein that you ate)– Glucose (from carbohydrates that you ate)– Lipids (from fats that you ate)

What does the cell membrane do?

What does the cell membrane do?

• The cell membrane lets things in and out of a cell.

What does the cell membrane do?• The cell membrane lets things in and out of a

cell. – Water– Oxygen– Glucose (sugar)– “Food”

• Amino acids (from meat protein that you ate)• Glucose (from carbohydrates that you ate)• Lipids (from fats that you ate)

Cellular Transport is the movement of

materials across the cell’s membrane.

Where is the cell membrane found?

• The cell membrane is found on the outside of animal cells

• The cell membrane is found under the cell wall in plant cells.

CELL MEMBRANE

Animal Cell Plant Cell

The Structure of the Cell Membrane

• The cell membrane is made up of molecules called phospholipids

Phospholipid

Quick Chemistry Review:

What is a Molecule?

Atomp+

n0

e-

Atoms and Molecules• The cell is the smallest LIVING UNIT.

The cell is the building block of life.

• But the basic building blocks for EVERYTHING in the Universe is the atom.–Atoms are NOT LIVING

Atoms and Molecules• If atoms are put together, they form

a molecule.

H H O+ + = O

HH

2 hydrogen atoms + 1 oxygen atom = water

Structural OrganizationOrganism

Organ System

Organ

Tissue

Cell

Organelle

Molecule

Atoms

Smallest living unit

Smallest unit

(Cell Membrane)

(Phospholipid)

The Structure of the Cell Membrane• Because the cell membrane is made up of 2 layers of phospholipids, it can also be called

the phospholipid bilayer.

Phospholipid Bilayer

The Structure of the Cell Membrane

Protein

Outside the Cell

Inside the Cell

Animal Cell

Selectively Permeable• A cell membrane is selectively

permeable, meaning that it will only let certain things go through the cell membrane.

There are Several Ways to Get Materials Across

the Cell Membrane

Does the Movement of the Materials Require Energy?

• If it DOES NOT require energy, it is called passive transport.

• If it DOES require energy, it is called active transport.

Passive Transport• There are 3 types of passive

transport:–Diffusion–Osmosis–Facilitated Diffusion

Diffusion• Diffusion is when atoms and

molecules move from an area of high concentration to an area of low concentration.

• (They move from where they are to where they are not.)

Diffusion

beginning of diffusion middle of diffusion equilibrium

This is what diffusion looks like.

Fun Fact• The reason that atoms and molecules always

move from an area where they are to an area where they are not is because they are trying to reach a state of equilibrium where all of the particles are evenly distributed through out.

beginning of diffusion middle of diffusion equilibrium

Diffusion

Protein

Diffusion can occur through the phospholipid bilayer (it does not require transport proteins or energy)

Of all the things a cell needs, what do you think moves in and out of the

cell by diffusion?

What moves in and out of the cell by diffusion?

• Oxygen• This is how oxygen makes its way from

your lungs to your blood stream and eventually to every cell you have.

Osmosis• Osmosis is the diffusion of water.• (Scientists thought since you are made up of

so much water and water is such a special molecule, that it needed its own separate term!)

Osmosis and Diffusion

Protein

Osmosis and diffusion can occur through the phospholipid bilayer (it does not require transport proteins or energy)

Facilitated Diffusion• When molecules are too big to

float past the cell membrane, they must go through proteins that are in the cell membrane instead.

• Example: glucose

Facilitated Diffusion

Protein

Facilitated Diffusion means the molecules must go through the transport proteins in the phospholipid bilayer.

Glucose

Facilitate = to help

So the proteins are helping the molecule cross the cell membrane.

Active Transport• Active transport is when the cell has

to use energy to get the transport proteins to pump atoms or molecules into or out of the cell.

Active Transport

Protein

Facilitated Diffusion means the atoms or molecules must use energy to go through the transport proteins in the

phospholipid bilayer.

energ

y

Why Would a Cell Need Energy to Do Active

Transport?What is it trying to

overcome?

Why Would a Cell Need Energy to Do Active Transport?

Because the cell already has too much of the atom or molecule (it has reached equilibrium) and if the cell requires more, it must use energy to overcome the tendency to reach equilibrium.

What If…• What if the particle is too big to

enter or leave the cell through transport proteins? How does the cell get that particle anyway?

What If…• What if the particle is too big to

enter or leave the cell through transport proteins? How does the cell get that particle anyway?–Endocytosis and Exocytosis

Endocytosis• In order for a cell to get the giant particle into

the cell, the cell must wrap part of its cell membrane around the particle and fold the whole thing into itself forming a vesicle.

Cell Cell Cell

Exocytosis• In order for a cell to get the giant particle out

of the cell, it must push the vesicle with the particle to the cell membrane and pop the particle back out of the cell.

CellCellCell

How does cell transport relate to

homeostasis?

Homeostasis• A cell does all of the different types of

transport to maintain a delicate balance of conditions inside the cell so it can live. This balance is called homeostasis.

Look at Page 79 in the Text

• Page 79 in the textbook is a fantastic illustration of all of the different types of transport in the cell.

Let’s See What You Have Learned

1. What does selectively permeable mean?

1. What does selectively permeable mean?

• It means that the cell membrane only lets certain things in and out of the cell.

2. How are osmosis and diffusion different?

2. How are osmosis and diffusion different?

• Diffusion is when particles enter the cell without using energy and without using transport proteins.

• Osmosis is the exact same thing as diffusion, only osmosis refers to the movement of water.

3. What is the difference between active and passive transport?

3. What is the difference between active and passive transport?

• Although both use transport proteins, active transport requires energy and passive transport does not.

4. What is the other name for the cell membrane?

4. What is the other name for the cell membrane?

• The phospholipid bilayer

Complete the TableType of Transport

Does It Require Transport Proteins?

Does It Require Energy?

Used for Large or Small Particles?

Does It Play a Role in Homeostasis?

Diffusion

Osmosis

Facilitated Diffusion

Active Transport

Endocytosis

Exocytosis

Complete the TableType of Transport

Does It Require Transport Proteins?

Does It Require Energy?

Used for Large or Small Particles?

Does It Play a Role in Homeostasis?

Diffusion No No Small Yes

Osmosis No No Water only (small)

Yes

Facilitated Diffusion

Yes No Large Yes

Active Transport

Yes Yes Any size Yes

Endocytosis No Large Yes

Exocytosis No Large Yes

Summary

Types of Cellular Transport

Does NOT Require Energy Requires Energy

OsmosisDiffusion Facilitated Diffusion

(Passive Transport) (Active Transport)

Anything that goes through the membrane

Water that goes through the membrane

Anything that goes through the membrane that needs the help of a transport protein, but not energy.

Anything that goes through the membrane that requires a transport protein and energy.