Cellular Transport

1. Cellular Transport Chapter 7, pages 201-207

2. Essential Question • How does a cell membrane help the cell maintain homeostasis?

3. Cellular Transport • Cellular transport is the movement of substances within the cell, into the cell, and out of the cell. • Mechanisms of cellular transport: • Diffusion • Simple diffusion • Facilitated diffusion • Osmosis • Active Transport • Transport of Large Particles

4. Diffusion: • is the movement of particles from a high concentration to a low concentration. • Movement takes place down a concentration gradient. • http://www.biosci.ohiou.edu/introbioslab/Bios170/diffusion/Diffusion.html

6. Three things affect the rate of diffusion: • Concentration – when concentration is high, diffusion occurs more quickly because there are more particles that collide. • Temperature • Pressure An increase in temperature or pressure will increase the number of collisions thus increasing the rate of diffusion.

7. Diffusion Across the Plasma Membrane • Cells require water, salts, sugars in order to function. • Water can diffuse freely across the plasma membrane. • Most other substances require help from transport proteins (channel proteins and carrier proteins). • Facilitated diffusion – uses transport proteins to move small molecules across the plasma membrane.

8. Transport proteins facilitating movement of small molecules into a cell: Outside Cell Inside Cell Channel Protein Carrier Protein http://www.youtube.com/watch?v=Qqsf_UJcfBc http://www.youtube.com/watch?v=s0p1ztrbXPY http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html

9. Osmosis • Osmosis is the diffusion of water across a selectively permeable membrane. • Water is the solvent in a cell and its environment.

10. Osmosis: diffusion of water across the plasma membrane

12. Cells in anisotonic solution – When a cell is in a solution that has the same concentration of water and solutes as its cytoplasm, the cell is said to be in an isotonic solution.

13. Cells in ahypotonic solution – If a cell is in a solution that has a lower concentration of solute, the cell is said to be in a hypotonic solution.

14. Cells in ahypertonic solution – When a cell is placed in a hypertonic solution, the concentration of the solute outside of the cell is higher than inside.

15. View animations for hypotonic, hypertonic, and isotonic solutions: http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

17. Transport of Large Particles • Substances that are too large to move through the plasma membrane by diffusion or transfer proteins get inside by a different process. This process is called…

18. Endocytosis • Endocytosis is the process by which: • a cell surrounds a substance that’s on the outside of the cell • It encloses the substance in a portion of the cell membrane • the membrane pinches off and leaves the substance on the inside of the cell. • http://highered.mcgraw-hill.com/olc/dl/120068/bio02.swf

19. Exocytosis • Exocytosis is the secretion of materials at the plasma membrane. It is the reverse of endocytosis. • Cells use exocytosis to expel wastes and to secrete substances, such as hormones, produced by the cells. • http://highered.mcgraw-hill.com/olc/dl/120068/bio02.swf

20. Both endocytosis and exocytosis require the input of energy.