Essential Question: How do materials get in and out of a cell?

• You learned in section 1 that the membrane does a lot to control what goes in & out of the cell.

• Today you will learn the specific ways materials enter & exit the cell.

• You will see that the way a cell gets each material it needs is unique and specialized.

• Also, that there are ways the cell gets its needed materials in or out by both using and not using energy.

Objectives: Passive & Active Transport

• Identify what determines the direction in which passive transport occurs.

• Understand osmosis and why it’s important.

• Illustrate how substances move against a concentration gradient in active transport.

Vocabulary

• Equilibrium• Concentration gradient• Diffusion• Carrier protein• Osmosis• Sodium-potassium pump

Before we get started…

• You’ll need to know these terms before we begin. Define these in your notebooks.

• Solute: A solid particle• Solvent: A liquid the dissolves solutes.• Solution: Solute dissolved in a solvent• Concentration: an amount of a substance within

a given volume

Passive Transport: Diffusion & Equilibrium

• In a solution, randomly moving molecules tend to fill up a space.

• Watch as I drop some food coloring into the beaker.

• What happens?• The process that causes this dispersion of polar

color molecules is diffusion.• When the space is filled evenly with the

particles, a state called equilibrium is reached.– A state that exists when the concentration of a

substance is the same through-out a space.

• Temperature– As the ice

melts the water temperature drops.

– The low temperature of the ice equalizes with the warmer water temp.

Equilibrium

Wa

ter

tem

p

Ice

Tem

p

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

• The amount of a particular substance in a given volume is called the concentration of the substance.

• When one area has a higher concentration than another area does, a concentration gradient exists. – The difference in the concentration of a

substance across a distance.

Passive Transport: Concentration Gradient

Do

wn

CO

NC

EN

TR

AT

ION

GR

AD

IEN

T

Up

Visual Concept: Concentration Gradient Area of High Concentration

Area of Low Concentration

• The movement of particles from regions of higher density to regions of lower density is diffusion.

• Watch as I drop food coloring into the beaker.• Would you all agree that the concentration of the

food coloring is highest right where it is dropped?

• Over time, the particles of color naturally diffuse through the water, without any need of physical movement.

Passive Transport: Diffusion

Diffusion

Visual Concept: DiffusionArea of High Concentration

Area of Low Concentration

Diffusion or Simple Diffusion

• One of the main jobs of the cell membrane is to separate the cytoplasm from the fluid outside the cell.

• But the cell still needs an abundance of materials that comes from outside the cell.

• Some substances that the cell needs can enter and leave the cell by diffusing across the cell membrane.

• The direction of movement depends on the concentration gradient, meaning that the particles will naturally flow where there is less of them, & usually where more is needed.

• The greatest part of this is…• DIFFUSION DOES NOT REQUIRE ENERGY!

Diffusion is Passive Transport

• In cells, diffusion through the membrane is called passive transport.

• In passive transport, substances cross the cell membrane down their concentration gradient.

• Some substances diffuse through the lipid bilayer.

• Other substances diffuse through transport proteins.

Small & Non-Polar:Diffuses directly through membrane

Small & Non-Polar:Diffuses directly through membrane

Large & or Polar:Cannot diffuse directly through membrane

Passive Transport & Not So Simple DiffusionFacilitated Diffusion• Facilitate means to help.• Many ions, large, and polar molecules that are important

for cell function do not diffuse easily through the nonpolar lipid bilayer.

• During facilitated diffusion, transmembrane proteins help these substances (large &/or polar) diffuse through the cell membrane.

• Two types of transport proteins:– channel proteins– carrier proteins.

Facilitated Diffusion: Passive Transport

Facilitated Diffusion through Channels• Ions, sugars, and amino acids can diffuse through the

cell membrane through channel proteins.

• These proteins, sometimes called pores, serve as tunnels through the lipid bilayer.

• Each channel allows the diffusion of specific substances that have the right size and charge.

Passive Transport, Facilitated Diffusion

Facilitate Diffusion: Through Carrier Proteins.•Carrier proteins transport substances that fit within their binding site.

– A protein that transports substances across a membrane

•A carrier protein binds to a specific substance on one side of the cell membrane. This binding causes the protein to change shape.

•As the protein’s shape changes, the substance is moved across the membrane and is released on the other side.

Visual Concept: Passive Transport: Facilitated Diffusion

Link to McGrawHill online (a good textbook) for animations and explanations of biology concepts.Take the quizzes!

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

Osmosis.• Water is essential for our survival. It is a critical molecule

in the production of ATP.– (without ATP we die)

• But water is polar & can’t go directly through the lipid bilayer.

• Water gets into the cell via a form of facilitated diffusion, called osmosis.– Water has its own channel protein through which it can diffuse.

Osmosis/ How the Environment Changes

• When ions and polar substances dissolve in water, they attract and bind some water molecules. The remaining water molecules are free to move around.

• If a concentration gradient exists across a membrane for solutes, a concentration gradient also exists across the membrane for free water molecules.

• Osmosis occurs as free water molecules move down their concentration gradient into the solution that has the lower concentration of free water molecules.

how_osmosis_works.html

Questions on Passive Transport?

• What is a concentration gradient?• What is diffusion?• What is passive transport?• What kinds of passive transport are there?• Does passive transport use energy?

Active TransportArea of High Concentration

Area of Low Concentration

Active Transport

• The opposite of diffusion is active transport.• In order to move substances against their

concentration gradients, cells must use energy.

• Active transport requires energy to move substances against their concentration gradients.

• Most often, the energy needed for active transport is supplied directly or indirectly by ATP.

Visual Concept: Comparing Active and Passive Transport

Link on sodium potassium pump = NO

http--www.stolaf.edu-people-giannini-flashanimat-transport-secondary%20active%20transport.swf

Active Transport, continued

Pumps• Pumps are carrier proteins that require energy to move

substances UP their concentration gradient.• The sodium-potassium pump is a carrier protein that

actively transports three sodium ions out of the cell and two potassium ions into the cell.– This pump is one of the most important carrier proteins in animal

cells. It prevents sodium ions from building up in the cell, resulting in osmosis into the cell… which could burst the cell.

– The concentration gradients of sodium ions and potassium ions also help transport other substances, such as glucose, across the cell membrane.

Sodium-Potassium Pump

Mass Transport Across a MembraneVesicles• Many substances, such as proteins, polysaccharides,

and even bacteria, are too large to be transported by carrier proteins altogether.

• Instead, they cross the cell membrane in vesicles, which are membrane-bound (lipid bi-layer) sacs.

• The vesicle membrane is a lipid bilayer, like the cell membrane. Therefore, vesicles can bud off from the membrane, fuse with it, or fuse with other vesicles.

Mass Transport Across a Membrane

Vesicles• Vesicles help the movement of large

molecules two ways:– Endocytosis– Exocytosis

http://wps.aw.com/bc_goodenough_boh_4/177/45510/11650562.cw/index.html

Endocytosis = “Into”Cell ingests large macromolecules or other cells

Vesicle

Exocytosis = “Exits”Opposite of EndocytosisRelease of contents in the cell to the external environment

Vesicle

Summary Questions • Does Passive Transport require Energy?• Does Active Transport require Energy?• What is the energy required for Active Transport?• What is the difference between active and passive transport?• Is diffusion Passive or Active?• Is Osmosis Passive or Active?• Is the Sodium-Potassium pump Passive or Active?• How would these substances get into the cell?

– Oxygen (non-polar)– Carbon dioxide (non-polar)– Glucose (a large non-polar substance)– Ions traveling down their concentration gradient (small polar)– Ions traveling up their concentration gradient (small polar)– Water (small polar molecule)– Amino acids (large molecules of varying polarity)

Concept Check

Summary

• In passive transport, substances cross the cell membrane down their concentration gradient.

• Osmosis allows cells to maintain water balance as their environment changes.

• Active transport requires energy to move substances against their concentration gradients.

Group Practice

• Get into groups and complete the worksheet. When completed, we will cover answers.

• Make sure to use the correct color for each molecule.

• At the end of class, turn in – Your completed Transport Practice Worksheet

• HW If not completed

– The HW from last night.

Take these Quizzes• http://www.hbwbiology.net/quizzes/ch8-cell-membrane.htm