Objectives Passive Active Transport Determine what passive transport

Objectives: Passive & Active Transport • Determine what passive transport is and what determines the how molecules cross a membrane in this way. • Define and 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. In the space next to this picture in your notes outline, DEFINE THE TERMS BELOW. • • Solute: A solid particle Solvent: A liquid that 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. – Movement of molecules through an fluid from an area of high concentration to low concentration. • 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 Water temp – As the ice melts the water temperature drops. – The low temperature of the ice equalizes with the warmer water temp. Ice Temp Equilibrium http: //highered. mc grawhill. com/sites/0072 495855/student_vi ew 0/chapter 2/anim ation__how_diffusi on_works. html

Passive Transport: Concentration Gradient • 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.

Down CONCENTRATION GRADIENT Up

Visual Concept: Concentration Gradient Area of High Concentration Area of Low Concentration

Passive Transport: Diffusion • RECALL: The movement of particles from regions of higher density to regions of lower density is diffusion. • Refer to the food coloring demonstration. • 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 for input of extra energy.

Diffusion

Visual Concept: Diffusion Area 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 across 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.

Passive Transport… Simple Diffusion directly through the membrane is SIMPLE DIFFUSION Simple Diffusion • Small, nonpolar molecules can pass directly through the lipid bilayer. This type of movement is called simple diffusion. • EXAMPLES OF SIMPLE DIFFSION • Oxygen moves down its concentration gradient into the cell. • Carbon dioxide diffuses out of the cell. • Natural steroid hormones, which are nonpolar and fat soluble, can also diffuse across the lipid bilayer.

Oxygen (O 2) Small & Non-Polar: Diffuses directly through membrane Large & or Polar: Cannot diffuse directly through membrane Carbon Dioxide (CO 2 Small & Non-Polar: Diffuses directly through membrane

Passive Transport & Not So Simple Diffusion Facilitated Diffusion • During facilitated diffusion, transmembrane proteins help these substances (large &/or polar) diffuse through the cell membrane. • 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. • Two types of transport proteins: – channel proteins – carrier proteins.

Facilitated Diffusion: Passive Transport Facilitated Diffusion through Channels • When molecules can freely flow through pores. • Ions, sugars, and amino acids can diffuse through the cell membrane through channel proteins. • These proteins, aka 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 Mc. Graw. Hill online (a good textbook) for animations and explanations of biology concepts. Take the quizzes! http: //highered. mcgrawhill. com/sites/0072495855/student_view 0/chapter 2/animati on__how_diffusion_works. html

Illustrate Facilitated Diffusion • Label the carrier protein. • Label the channel protein. • Illustrate which protein what would go through.

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 (called an aquaporin) through which it can diffuse.

how_osmosis_works. html 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.

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 Transport Area 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 (up) 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-gianniniflashanimat-transportsecondary%20 active%20 transport. 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 Membrane Vesicles • 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 Endocytosis Release 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 medium 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)

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.

Concept Check

Take these Quizzes • http: //www. hbwbiology. net/quizzes/ch 8 -cellmembrane. htm