1. Cells and Their Environment

2. Sections 1 & 2 Passive transport Movement that does not require energy from the cell Examples: Diffusion, Osmosis, and Crossing the cell membrane Active transport Movement across the cell membrane against its concentration gradient Movement against a concentration gradient Movement in vesicles Membrane receptor proteins

3. Passive Transport Movement across the cell membrane that does not require energy from the cell Substances move from areas of high concentration to areas of low concentration This is known as the concentration gradient

4. Equilibrium When the substances are equally divided among all areas then they have reached equilibrium Concentration of a substance is equal throughout a space

5. Movement of Substances Diffusion describes the movement of a substance from an area of high concentration to an area of lower concentration This is caused by the random motion of particles in a substance

6. Diffusion Across the cell Membrane Many molecules and ions enter or exit the cell by diffusing across the membrane Concentration inside the cell verses concentration outside the cell Cell membrane is selectively permeable

7. Osmosis The process in which water diffuses through the selectively permeable cell membrane. Type of passive transport (high to low) The direction of water movement depends on relative concentrations of water molecules

8. Directions of Water Movement Hypertonic - water moves out of the cell (shrinks) Hypotonic - water moves into the cell (bursts) Isotonic - no net movement of water (same concentration inside/outside of the cell)

9. Crossing the Cell Membrane Channels - transport proteins provide polar passageways through which ions and polar molecules can move across the cell membrane Each channel only allows a specific substance to pass through

10. Diffusion Through Ion Channels Ion channels - a transport protein within which an ion can pass through (Na+, Cl-, K+, Ca 2+ ) Ion can pass through the cell membrane without contacting the nonpolar interior of the lipid bilayer

11. Ion Transport (Electrical Charge) Movement across the membrane is also influenced by the particle’s positive or negative charge Opposite charges attract, like charges repel Typically, inside of cell is more negatively charged

12. Facilitated Diffusion Facilitated Diffusion is a type of passive transport that moves substances down their concentration gradient without using the cells’ energy Carrier proteins are used to move amino acids & sugars

13. Active Transport The transport of substances across the membrane against its concentration gradient is called active transport Amino acids, sugars, and other substances must be transported from outside the cell into cytoplasm Active Transport requires cell energy (ATP)

14. Sodium-Potassium Pump Na+K+ Pump transports 3 Na+ ions out of a cell and 2 K+ into the cell. Na+ is more concentrated outside the cell and K+ is more concentrated inside the cell - against concentration gradient

15. Purposes of Na/K Pump Prevents Na from accumulating inside cell. Too much Na would cause water to enter into cell by osmosis, causing cell to burst Na/K pump helps maintain ion concentration levels, which are used to transport glucose and other substances across the cell membrane.

16. Movement In Vesicles Movement into cell by a vesicle- endocytosis Vesicles form pouch, may fuse w/ a lysosome to move into cell. Movement out of the cell by vesicle -exocytosis Cells use exocytosis to export proteins (examples are nerve cells and glands )

17. Receptor Proteins Cells must respond to important information sent by hormones. Cells can receive messages b/c of receptor proteins in cell membrane bind to signal molecules. The binding of a signal molecule by its complementary receptor proteins causes a change in the receiving cell. The change can occur in 3 ways. –Changing permeability of cell (allows ions to cross) –Triggering formation of second messenger inside cell –Activating enzymes inside the cell (speed up reactions)

18. A Brief Review Passive Transport: Movement w/o energy Diffusion - movement from high to low conc. Osmosis- movement of water through c.m. Ion channels - helps ions across c.m. Facilitated Diff.- substance moves down concentration gradient Active Transport: Movement w/ energy Na/K Pump - uses ATP to move Na/K Endo/Exocytosis Signal molecules become bound to receptor proteins