Cell Transport

1. Cell Transport Facilitated Diffusion Cells in their Environment Active Transport

2. Passive Transport • Diffusion- movement of molecules from an area of high concentration to an area of low • Osmosis- process by which water molecules diffuse across a cell membrane from an area of high concentration to an area of low • Facilitated Diffusion- used for molecules that cannot readily diffuse through cell membranes, even when there is a concentration gradient…

3. Facilitated Diffusion • Facilitated Diffusion- carrier proteins in the cell membrane assist molecules that cannot readily diffuse across the cell membrane • Molecules cannot diffuse because: • May be not soluble in lipids • May be too large to pass through • Carrier proteins move molecules from a higher to lower concentration, so no energy is required… so it is PASSIVE TRANSPORT! • http://www.northland.cc.mn.us/biology/Biology1111/animations/active1.swf

4. Example of Facilitated Diffusion • Example= Glucose • Cells depend on glucose for energy • glucose molecules are too large to diffuse by simple diffusion • When glucose levels in cell are lower than outside the cell, carrier proteins transport glucose in

5. Cells in Hypotonic/ Hypertonic Environments • Cells exposed to an isotonic environment usually have no trouble keeping the movement of water across the membrane in balance. • It is more difficult for cells in a hypotonic/hypertonic environment • Contractile Vacuoles • Turgor Pressure • Plasmolysis • Cytolysis

6. Contractile Vacuoles • Unicellular freshwater organisms that live in a hypotonic environment use contractile vacuoles to rid excess water • Contractile Vacuoles- organelles that collect excess water and then contract to pump the water out of the cell • Pumping action requires cell to expend energy, it is not a form of passive transport

7. Cytolysis • Red Blood Cells- Lose their normal shape when exposed to an environment that is not isotonic • Hypertonic environment = water leaves/ cells shrink and shrivel • Hypotonic environment = water diffuses into cell/ cells swell and burst  Cytolysis • Cytolysis – bursting of cells

8. Turgor Pressure • Most plant cells live in hypotonic environment-water moves into plant cells by osmosis • Cells fill as they swell with water until cell membrane is pressed against cell wall • Cell wall resists pressure exerted by water • Turgor Pressure- the pressure that water molecules exert against cell wall

9. Plasmolysis • Plasmolysis- cells are in a hypertonic environment and water leaves through osmosis. Cells shrink away from the cell walls (turgor pressure is lost) • This is the reason plants wilt if they don’t receive enough water

10. Active Transport • Active Transport- movement of materials from an area of lower concentration to an area of higher concentration. Requires a cell to expend energy. • Endocytosis • Pinocytosis • Phagocytosis • Exocytosis • Sodium-Potassium Pumps

11. Endocytosis • Endocytosis- process by which cells ingest external fluid, macromolecules, and large particles • External materials are enclosed by a portion of the cells membrane- folds into itself/ forms a pouch • Pouch pinches off and becomes a vesicle • Pinocytosis- transport of solutes/ fluids • http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/pinocyt.html • Phagocytosis- movement of large particles • http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/phagocyt.html

12. Exocytosis • Exocytosis- process by which a substance is released from the cell through a vesicle (reverse of endocytosis) • Vesicles release their contents to the cell’s external environment • Ex: large molecules such as proteins, waste products, toxins • http://www.coolschool.ca/lor/BI12/unit4/U04L05/exocytosis.html

13. Sodium-Potassium Pumps • Sodium-Potassium pump – moves substance (ions) from lower to higher concentration/ require energy • Energy needed for active transport is supplied directly or indirectly by ATP • http://highered.mcgraw-hill.com/olc/dl/120068/bio03.swf