2. Passive and Active Transport

3. Importance Every living cell exists in a liquid environment. One of the most important functions of the cell membrane is to keep the cell’s internal conditions relatively constant. It does this by regulating the movement of molecules from one side of the membrane to the other side.

4. Passive Transport Cell membranes help organisms maintain Homeostasis by controlling what substances may enter or leave cells Doing this WITHOUT energy is called passive transport  Diffusion  Facilitated Diffusion  Osmosis

5. Diffusion The simplest form of passive transport Does not require energy Is the movement of molecules from an area of HIGH concentration to an area of LOW concentration High concentration of dye Low concentration of dye Ex: Perfume or Cologne

6. Facilitated Diffusion Most molecules cannot cross the cell membrane by simple diffusion Some Molecules are CARRIED across by CARRIER PROTEINS EMBEDDED IN the Cell Membrane Requires NO energy

7. Carrier Proteins CHANGE SHAPE when Molecules ATTACH to them The Change in Shape of the Carrier Protein ENABLES the Molecule to CROSS the Membrane. The use of carrier proteins is called facilitated diffusion.

8. Osmosis The diffusion of WATER over a semi- permeable membrane Does NOT require energy From HIGH concentration of WATER to LOW concentration of WATER

9. Osmotic Conditions Isotonic Hypertonic Hypotonic

10. Quick Chemistry Review Solute: substance being dissolved Solvent: water (does the dissolving) Solution: combined mixture

11. Isotonic “same strength” In an Isotonic solution  The amounts of solutes inside is the same as outside of cell  Under these conditions, water diffuses into and out of the cell at EQUAL RATES, so there is NO net movement of water  Remains at equilibrium “Like a full restaurant – one family must leave for another to enter”

12. Cells in isotonic solutions… No net movement of water Cells are normal

13. Hypertonic “above strength” The concentration of solute molecules outside the cell is higher than the concentrations of solutes inside the cell. WATER DIFFUSES OUT OF THE CELL until Equilibrium is established Plasmolysis: the cell shrinks “Hyper kids run out of school”

14. Cells in hypertonic solutions… Water moves out of the cell Cells shrivel (plasmolysis)

15. Hypotonic “blow strength” The concentration of solute molecule outside the cell is lower than the concentration of solutes inside the cell WATER DIFFUSES INTO THE CELL until Equilibrium is established Cytolysis: the cell explodes

16. Cells in hypotonic solutions… Water moves into the cell Animal cells burst (cytolysis) Plant cells become turgid

17. Cells in Osmotic Environments Plasmolysis (Elodea cell) Cytolysis (Tumor cell) Isotonic (Elodea cell)

18. Active Transport In many cases, cells must move materials from an area of low concentration to high concentration This requires energy When energy is used to transport molecule across a membrane, this is called active transport

19. Small molecules and ions are carried across membranes by proteins in the membrane that act like pumps Large molecules need to be transported in Bulk Bulk transports include endocytosis, and exocytosis

20. Endocytosis During ENDOCYTOSIS the Cell Membrane folds into a POUCH that encloses the Particles. The Pouch pinches off INSIDE the Cell to form a VESICLE (membrane- wrapped bubbles). The VESICLE can then fuse with other Organelles or release its contents into the cytoplasm

21. Pinocytosis and Phagocytosis Two forms of Endocytosis Pinocytosis is often referred to as “cell drinking”  Bring in fluids and solutes Phagocytosis is often referred to as “cell eating”  Brings in food or other cells

22. Exocytosis The opposite of endocytosis  Gets rid of wastes