Active Transport, Diffusion and Osmosis

Passive Transport by Diffusion

• Diffusion is the movement of molecules from an area of high concentration to an area of low concentration.(down the concentration gradient)

• Diffusion does not refer only to movement across a membrane.

How Diffusion Works

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

Passive Transport by Osmosis

• Osmosis is the movement of water across a biological membrane.

• Water molecules move from an area of low concentration solute (hypotonic) to an area of high concentration (hypertonic)

• Water moves because the membrane is impermeable to the solute

Affect of Osmosis

http://www.etomica.org/app/modules/sites/Osmosis_old/Background1.html

Affect of Osmosis

http://en.wikipedia.org/wiki/User:Reo_On/Passive_transport

How Osmosis works

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

Passive transport by Facilitated Diffusion

• Molecules can enter a cell by diffusion through a specific channel proteins or carrier proteins embedded in the membrane

• This process mediated by a membrane protein is called facilitated diffusion

• Molecules move down the concentration gradient

Channel Proteins

• Form highly specific channel through the cell membrane

• Permit the passage of ions or polar molecules

• Some channel proteins remain open all the time, others have gates that can be opened or closed to allow or prevent the passage of particles

http://www.biologycorner.com/APbiology/cellular/(notes)cell_membrane.html

Carrier Proteins

• Bind to specific molecules, transport them across the membrane and release them

• Carrier molecules change shape while transporting molecules

• Usually transport ions or small polar molecules but can also transport amino acids and glucose

• Have a lower rate of diffusion than channel proteins

Channel and Carrier Proteins

http://www.ncbi.nlm.nih.gov/books/NBK9928/

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

Active Transport

• Active transport is the movement of ions, molecules or minerals from an area of low concentration to an area of high concentration(against the concentration gradient)

• This requires energy in the form of ATP

Primary Active Transport

• Uses ATP directly to move molecules or ions from one side of the membrane to the other

• Ion pumps are carrier proteins that pump ions against the concentration gradient

• The sodium-potassium pump pumps Na+ out of the cell and K+ ions into the cell

http://saddlebackphysio.blogspot.com/2010/09/membrane-transportjust-passin-through.html

How the Sodium-Potassium pump works

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

Secondary Active Transport

• As an ion pump functions, a difference in charge, or electrical potential, builds up across the membrane

• One side of the membrane gains a more positive or negative charge compared to the other side due to the accumulation of positive or negative ions

Secondary Active Transport

• The combination of concentration gradient and electrical potential is called an electrochemical gradient

• This gradient stores potential energy that can be used by the cell

• This energy is used by another protein to transport other molecules across a membrane

Electrochemical Gradient

http://bioap.wikispaces.com/Ch+7+Collaboration+2010

http://www.cetbiology.com/support/biology-photographs.html

Membrane-Assisted Transport

• Macromolecules are too large to cross the cell membrane through a channel or by means of a carrier protein

• Cells form vesicles to surround incoming or outgoing material and move it across the cell membrane

• Membrane-assisted transport requires energy

Endocytosis

• The process where a cell engulfs material by folding the cell membrane around it and then pinching it off to form a vesicle inside

• There are three methods:– Pinocytosis– Phagocytosis– Receptor-mediated endocytosis

Receptor-mediated Endocytosis

http://www.yellowtang.org/cells.php

Pinocytosis

http://www.yellowtang.org/cells.php

Phagocytosis

http://www.yellowtang.org/cells.php

Exocytosis

• Macromolecules and other large particles leave a cell by exocytosis

• Vesicles that contain cell products to be released or waste products to be excreted fuse with the cell membrane and empty their contents into the extracellular environment

http://www.linkpublishing.com/video-transport.htm

Phagocytosis

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