1. ENDURING UNDERSTANDING 2.B GROWTH, REPRODUCTION AND DYNAMIC HOMEOSTASIS REQUIRE THAT CELLS CREATE AND MAINTAIN INTERNAL ENVIRONMENTS THAT ARE DIFFERENT FROM THEIR EXTERNAL ENVIRONMENTS. ESSENTIAL KNOWLEDGE 2.B.2 GROWTH AND DYNAMIC HOMEOSTASIS ARE MAINTAINED BY THE CONSTANT MOVEMENT OF MOLECULES ACROSS MEMBRANES. BIG IDEA II BIOLOGICAL SYSTEMS UTILIZE FREE ENERGY AND MOLECULAR BUILDING BLOCKS TO GROW, TO REPRODUCE AND TO MAINTAIN DYNAMIC HOMEOSTASIS.

2. ESSENTIAL KNOWLEDGE 2.B.2: GROWTH AND DYNAMIC HOMEOSTASIS ARE MAINTAINED BY THE CONSTANT MOVEMENT OF MOLECULES ACROSS MEMBRANES. Learning Objectives: (2.12) The student is able to use representations and models to analyze situations or solve problems qualitatively and quantitatively to investigate whether dynamic homeostasis is maintained by the active movement of molecules across membranes.

3. PASSIVE TRANSPORT Passive Transport is the diffusion of a substance across a semi-permeable membrane from an area of high concentration to an area of low concentration WITHOUT the use of energy. Passive transport plays a primary role in the import of resources and the export of wastes. Diffusion is the tendency for molecules to spread out evenly into the available space. Although each molecule moves randomly, diffusion of a population of molecules may exhibit a net movement in one direction. At dynamic equilibrium, as many molecules cross one way as cross in the other direction. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

4. Fig. 7-11 Molecules of dye Membrane (cross section) WATER Net diffusion Equilibrium (a) Diffusion of one solute Net diffusion Equilibrium (b) Diffusion of two solutes

5. PASSIVE TRANSPORT Substances diffuse down their concentration gradient, the difference in concentration of a substance from one area to another. No work must be done to move substances down the concentration gradient. The diffusion of a substance across a biological membrane is passive transport because it requires no energy from the cell to make it happen. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

6. DIFFUSION EXISTS IN TWO FORMS: DIALYSIS AND OSMOSIS Dialysis: the PASSIVE movement of particles across a semi-permeable membrane from an area of high concentration to an area of low concentration (no energy) Osmosis: the PASSIVE movement of water molecules across a semi-permeable membrane from an area of high concentration to an area of low concentration (no energy)

7. EFFECTS OF OSMOSIS ON WATER BALANCE Osmosis is the diffusion of water across a selectively permeable membrane Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration THIS MEANS THAT WATER ALWAYS ATTEMPTS TO DILUTE!!!! Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

8. Lower concentration of solute (sugar) Fig. 7-12 H2OH2O Higher concentration of sugar Selectively permeable membrane Same concentration of sugar Osmosis

9. WATER BALANCE OF CELLS WITHOUT WALLS Tonicity is the ability of a solution to cause a cell to gain or lose water Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

10. Fig. 7-13 Hypotonic solution (a ) Animal cell (b ) Plant cell H2OH2O Lysed H2OH2O Turgid (normal) H2OH2O H2OH2O H2OH2O H2OH2O Normal Isotonic solution Flaccid H2OH2O H2OH2O Shriveled Plasmolyzed Hypertonic solution

11. OSMOREGULATION Hypertonic or hypotonic environments create osmotic problems for organisms Osmoregulation, the control of water balance, is a necessary adaptation for life in such environments The protist Paramecium, which is hypertonic to its pond water environment, has a contractile vacuole that acts as a pump Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

12. Fig. 7-14 Filling vacuole 50 µm (a) A contractile vacuole fills with fluid that enters from a system of canals radiating throughout the cytoplasm. Contracting vacuole (b) When full, the vacuole and canals contract, expelling fluid from the cell.

13. WATER BALANCE OF CELLS WITH WALLS Cell walls help maintain water balance A plant cell in a hypotonic solution swells until the wall opposes uptake; the cell is now turgid (firm) If a plant cell and its surroundings are isotonic, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

14. WATER BALANCE OF CELLS WITH WALLS In a hypertonic environment, plant cells lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called plasmolysis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

15. FACILITATED DIFFUSION In facilitated diffusion, transport proteins speed the passive movement of molecules across the plasma membrane Channel proteins provide corridors that allow a specific molecule or ion to cross the membrane - Facilitated diffusion is still passive because the solute moves down its concentration gradient Channel proteins include – Aquaporins, for facilitated diffusion of water – Ion channels that open or close in response to a stimulus ( gated channels ) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

16. Fig. 7-15 EXTRACELLULAR FLUID Channel protein (a) A channel protein Solute CYTOPLASM Solute Carrier protein (b) A carrier protein

17. ACTIVE TRANSPORT Active Transport uses free energy to move molecules AGAINST their concentration gradients via proteins imbedded in the cell membrane Some transport proteins, however, can move solutes against their concentration gradients Active transport is a process where free energy (often provided by ATP) is used by proteins embedded in the membrane to “move” molecules and/or ions across the membrane and to establish and maintain concentration gradients. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

18. Fig. 7-17 Passive transport Diffusion Facilitated diffusion Active transport ATP

19. FIGURE 8.15 THE SODIUM-POTASSIUM PUMP: A SPECIFIC CASE OF ACTIVE TRANSPORT

20. HOW ION PUMPS MAINTAIN MEMBRANE POTENTIAL Membrane potential is the voltage difference across a membrane Voltage is created by differences in the distribution of positive and negative ions Two combined forces, collectively called the electrochemical gradient, drive the diffusion of ions across a membrane: A chemical force (the ion’s concentration gradient) An electrical force (the effect of the membrane potential on the ion’s movement) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

21. CELLULAR PUMPS An electrogenic pump is a transport protein that generates voltage across a membrane The sodium-potassium pump is the major electrogenic pump of animal cells The main electrogenic pump of plants, fungi, and bacteria is a proton pump Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

22. Fig. 7-18 EXTRACELLULAR FLUID H+H+ H+H+ H+H+ H+H+ Proton pump + + + H+H+ H+H+ + + H+H+ – – – – ATP CYTOPLASM –

23. COTRANSPORT Cotransport is coupled transport by a membrane protein Cotransport occurs when active transport of a solute indirectly drives transport of another solute Plants commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

24. Fig. 7-19 Proton pump – – – – – – + + + + + + ATP H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Diffusion of H + Sucrose-H + cotransporter Sucrose

25. BULK TRANSPORT Bulk transport across the plasma membrane occurs by exocytosis and endocytosis Small molecules and water enter or leave the cell through the lipid bilayer or by transport proteins Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles Bulk transport requires energy Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

26. Fig. 7-20 PHAGOCYTOSIS EXTRACELLULAR FLUID CYTOPLASM Pseudopodium “Food”or other particle Food vacuole PINOCYTOSIS 1 µm Pseudopodium of amoeba Bacterium Food vacuole An amoeba engulfing a bacterium via phagocytosis (TEM) Plasma membrane Vesicle 0.5 µm Pinocytosis vesicles forming (arrows) in a cell lining a small blood vessel (TEM) RECEPTOR-MEDIATED ENDOCYTOSIS Receptor Coat protein Coated vesicle Coated pit Ligand Coat protein Plasma membrane A coated pit and a coated vesicle formed during receptor- mediated endocytosis (TEMs) 0.25 µm

27. EXOCYTOSIS In exocytosis, transport vesicles migrate to the membrane, fuse with it, and release their contents Many secretory cells use exocytosis to export their products (proteins). In what part of the cell were these proteins made? The ER or cytoplasm? Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

28. ENDOCYTOSIS In endocytosis, the cell takes in macromolecules by forming vesicles from the plasma membrane Endocytosis is a reversal of exocytosis, involving different proteins There are three types of endocytosis: Phagocytosis (“cellular eating”) Pinocytosis (“cellular drinking”) Receptor-mediated endocytosis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

29. PHAGOCYTOSIS & PINOCYTOSIS In phagocytosis a cell engulfs a particle in a vacuole The vacuole fuses with a lysosome to digest the particle In pinocytosis, molecules are taken up when extracellular fluid is “gulped” into tiny vesicles In receptor-mediated endocytosis, binding of ligands to receptors triggers vesicle formation A ligand is any molecule that binds specifically to a receptor site of another molecule Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings