Cell Membrane is the “transportation highway” it controls what goes in and out of a cell

1. Cell Membrane is the “transportation highway” it controls what goes in and out of a cell To perform their functions, cells must maintain a steady state in the midst of an ever-changing environment. Steady state is maintained by regulating the movement of materials into and out of the cell.

2. Transport Across Membranes • Regulating the movement of materials into and out of the cell is a major role of the cell membrane. • The cell membrane is selectively permeable – allowing some substances to cross more easily than others.

3. The molecular structure of the cell membrane is a phospholipidbilayer (hydrophilic exterior and interior and a hydrophobic core). • Because of its structure, factors such as the size of the molecule, whether it is hydrophobic or hydrophilic, and the tonicity of the solution are all potential factors affecting transport across it. Plasma Membrane http://www.youtube.com/watch?v=Rl5EmUQdkuI&feature=fvwrel

4. Our laboratory experiments will explore the mechanism that move molecules across cell membranes. • The means by which molecules move across membranes are either active (energy expended) or passive (no energy expended) transport. Plasma Membrane http://www.youtube.com/watch?v=Rl5EmUQdkuI&feature=fvwrel

5. Passive Transport Definition:The movement of a substance across the membrane with no energy investment. • Includes: Diffusion Osmosis Facilitated Diffusion Passive Transport Video http://www.brainpop.com/science/cellularlifeandgenetics/passivetransport/

6. Diffusion • Definition Spontaneous process by which molecules move from a region where they are highly concentrated to a region in which their concentration is lower. • Results from the kinetic activity of molecules (constant motion)

7. Diffusion Passive process that moves molecules from high concentration to low (across cell membranes when permeable). http://www.biologycorner.com/bio1/diffusion.html Diffusion Video http://www.brainpop.com/science/matterandchemistry/diffusion/

8. Concentration

9. Concentration Gradient

11. Osmosis Definition Diffusion of water across a selectively permeable membrane. Water moves from its highest concentration or potential to its lowest concentration or potential. Pure water has the highest potential. The more solute dissolved in water the lower the potential. .

12. Osmosis • Maintaining the water content of the cell is CRITICAL to the functioning of all plant and animal cells. Osmosis http://www.youtube.com/watch?v=sdiJtDRJQEc

13. Tonicity Definition:The ability of a solution to cause a cell within it to gain or lose water Tonicity of a solution depends in part on its concentration of solutes that cannot cross the membrane.

14. Isotonic • "ISO" means the same • If the concentration of solute (salt) is equal on both sides, the water will move back in forth but it won't have any result on the overall amount of water on either side.

15. Hypotonic • The word "HYPO" means less, in this case there are less solute (salt) molecules outside the cell, (and more water molecules). Therefore, water moves from its highest concentration outside the cell into the cell. • The cell will gain water and grow larger.

16. Hypotonic • When placed in a hypotonic solution:Animal cells, lacking a rigid cell wall, are in danger of bursting, called hemolysis. In some cases organelles called contractile vacuoles will pump water out of the cell to prevent this. In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid (called turgor), the cell wall keeps the plant cell from bursting

17. Hypertonic • The word "HYPER" means more, in this case there are more solute (salt) molecules outside the cell, which causes the water to leave the cell (again moving from high water concentration inside the cell to a lower concentration outside the cell).

18. When Placed in Hypertonic Solution • Plant cells, the central vacuole loses water and the cells shrink, causing wilting. • Animal cells, the cells also shrink, called crenation. • In both cases, the cell may die.

20. Key Concepts • Regulating the movement of materials into and out of the cell is a major role of the cell membrane. • Membrane structure results in selective permeability. • Passive transport is diffusion of a substance across a membrane with no energy investment • Active transport uses energy to move solutes against their gradients. • Maintaining the water content of the cell is CRITICAL to the functioning of all plant and animal cells.

21. Key Concept Video Passive Transport – Diffusion, Facilitated Diffusion, and Osmosis http://www.youtube.com/watch?v=JShwXBWGMyY&feature=fvsr

22. Active Transport • Energy is expended by the cell to move a molecule across its membrane against its concentration gradient. (moving it from low concentration to high). • Important in maintaining ion concentrations and water balance in many cells.

23. Active Transport • Organisms living in fresh water are immersed in a hypotonic solution. • Water moves into their cells. Some cells handle this by actively removing the water. • ATP is expended to move water out of the cell against its concentration gradient (low concentration of water inside the cell, high concentration of water outside the cell).

24. Active Transport Definition Process uses energy to move solutes across the membrane (against their gradients) Includes:Solute pumps Exocytosis Endocytosis – Phagocytosis and Pinocytosis Active Transport http://www.brainpop.com/science/cellularlifeandgenetics/activetransport/