• The purpose of a cell membrane is to separate the environments inside and outside of the cell and to regulate what comes in and out.

Cell Membrane

•Molecules are constantly moving.•Collisions between moving molecules will

spread the molecules apart until they are evenly distributed throughout the available space. • http://phet.colorado.edu/en/simulation/gas-

properties

Molecules have Kinetic Energy

•Cell Transport: Movement of Molecules across a cell membrane. • The Cell Membrane is semi-permeable

meaning only some molecules will be able to be transported across the membrane.

How do Cells Regulate what comes in and out of the cell?

I. Diffusion• Molecules are not

stationary, instead they are constantly moving about

• Molecules have energy of motion (kinetic energy)

• Collisions between moving molecules will spread the molecules apart until the molecules are evenly distributed throughout the available space

• The movement of molecules from an area of high concentration to an area of low concentration is called diffusion.• Ex. Perfume diffusing through the air• Food coloring diffusing in water

II.Permeability• A material is permeable if it allows

molecules to pass through.• The cell membrane (plasma

membrane) is permeable.

Hey, sponges are permeable too!!

III. Osmosis• Osmosis is the diffusion of water molecules

across a permeable membrane. • In osmosis, like diffusion, water molecules

move from an area of high concentration to low.

• Hypotonic solutions-Solutions which contain a

lower concentration of dissolved substances than a solution to which it is being compared.

In a hypotonic solution the cell swells or possibly explodes

Red blood cell placed in distilled water

• Hypertonic Solution• Solutions which

contain a higher concentration of dissolved substances than the solution to which it is being compared

• In hypertonic solutions the cell shrinks

Red blood cell placed in salt water solution

• Isotonic solutions• When the solution

inside the membrane is the same concentration as the solution outside the membrane.

• An isotonic solution is at equilibrium

• In an isotonic solution there is no change in the cell

Red blood cell in an isotonic solution

A B C D E

•Which is the most hypertonic solution?

•Which is the most hypotonic solution?

•Which solution is isotonic?

• Osmosis is one way that plants take in water through their root cells.

• Plant cells use osmosis to build up a large positive internal pressure, the turgor pressure.

• Turgor pressure determines the rigidity and stability of plant tissues.

• Plants that lose turgor pressure wilt.

• Both Osmosis and Diffusion are types of passive transport.

• Passive transport requires no input of energy from the cell.

• Passive Transport: requires no energy.• Examples of passive transport:

1. diffusion: movement of molecules from high concentration to low concentration.

2. osmosis: movement of water across a permeable membrane from an area of

high concentration to low concentration.

• BUT: There are some molecules that are too large to pass through the phospholipid bilayer.

• Therefore, some molecules must undergo passive transport by means of transport proteins.

• This is called:FACILITATED DIFFUSION

• There are two types of transport proteins:

 

1. channel proteins

2. carrier proteins

• Channel proteins are tube like and provide openings through which particles can diffuse.

• Carrier proteins have a specific shape that fits a specific molecule.

• When the proper molecule combines with the protein, it changes shape and moves the molecule across the membrane.

• Facilitated diffusion is passive and requires no energy.

• Can a cell ever move particles from a region of lesser concentration to a region of greater concentration?

 • Yes, but energy must counteract the

tendency of the molecules to move in the opposite direction.

• The transport of materials against a concentration gradient requires energy (ATP) and is called ACTIVE TRANSPORT.

• First a transport protein binds with the substance to be transported.

• Energy from the cell is used to change the shape of the proteins so that the particle is released on the other side of the membrane.

• Once the particle is released, the protein regains its’ original shape.

• Some cells can take in large molecules, groups of molecules, or even whole cells through ENDOCYTOSIS.

• The reverse process of endocytosis is EXOCYTOSIS. Cells use this to expel wastes, and secrete cellular products.

                                                                   

• PASSIVE TRANSPORT:• 1. no energy• 2. movement of

molecules from high concentration to low concentration.

• 3. Examples:• diffusion, osmosis,

facilitated diffusion

• ACTIVE TRANSPORT:• 1. requires energy• 2. movement of molecules

from low concentration to high concentration.

• 3. use of transport proteins• 4.exocytosis and

endocytosis are active transport for large molecules, wastes, and cellular products. 

1. The diffusion of water molecules across a permeable membrane is called ________.

2. The movement of molecules from an area of high concentration to an area of low concentration is called ___________.

3. Describe each of the following solutions: hypotonic, hypertonic, and isotonic solutions.

4. What is turgor pressure and why is it important for plants?

5. Both osmosis and diffusion are examples of ___________ transport.

1.What is passive transport?2. List and describe the different types of passive

transport. 3. What is active transport?4. List and describe the different types of active

transport.5. List the two types of transport proteins. When

the transport proteins are used, is it active or passive transport?