Cell Membrane and Homeostasis: Maintaining Balance Within Cells

1. Chapter 5 Homeostasis and Transport

2. What part of a cell maintains it homeostasis? Cell Membrane is selectively permeable Regulates what goes in and out of a cell

3. Passive transport – movement of molecule across a cell membrane w/o energy expenditure. Types of Passive transport • Diffusion • Osmosis • Facilitated Diffusion • Ion Channels

4. Low The steeper the slope, the faster the rate of diffusion. Therefore, the greater the concentration differential, the faster the rate of diffusion High • Diffusion – movement of molecules from an area of [High] to an area of [low]. Concentration gradient - No energy is required to go from High to low [ ]. Totally driven by molecules’ kinetic energy – constant motion. Demos with Air freshener, Potassium Permangenate

5. Movement of molecules continues until they reach Equilibrium • An increase in temperature, > the kineticenergy of the molecules therefore diffusion occurs faster. • Why sugar “melts” faster in hot water over cold • May occur across the cell membrane • Dependant on: • size of molecules • size of pores • & solubility of molecules (CO2 & O2) easily go into solution into bilipid layer. Demo with Ammonia and phenolphthalein

6. Osmosis - [ ] means concentration - net movement of water from [high] ---> [low] through a membrane Direction of water movement depends on the [ ] of solutes on 2 sides (inside the cell and outside the cell Water Molecules move from where there is a lower solute concentration to a higher solute concentration

7. Demonstration of osmosis What is happening to: the water (blue) and the dissolved substances (green and red). What is the same? What is different?

8. Hypertonic • Hypertonic Solution: [Solute] outside the cell is higher than inside the cytosol • More dissolved particles outside of cell than inside of cell • Hyper = more; • Tonic = dissolved particles/solutes • Water moves out of cell into solution • Cell shrinks • What happens when you put salt on a slug?

9. Red Blood Cells in a normal solute concentation, freshwater and then salt

10. Elodea Plasmolysis* -  loss of cytoplasmic structure due to water.

11. Hypotonic

12. Hypotonic Solution: [Solute] concentration outside is lower than cytosol • Less dissolved particles outside of cell than inside of cell • Hypo = less, under • Tonic = dissolved particles/solute • Water moves into cell from solution • Cell expands(and may burst)

13. Hypotonic • Turgidity -  swollen cells due to water gain. Plant cells depend on this! • Cytolysis (bursting) may result.

14. Isotonic Solution: • Solute concentration of solution equal to that of cell • No net water movement • Most cells exists in an isotonic external environment

17. Turgor Pressure Plasmyolysis

18. Plants usually exist in a hypotonic environment. • Cells don’t burst due to flexible & strong cell wall. • Turgor pressure – pressure exerted by water on a plant’s cell wall.

20. Part 2 of Diffusion/Osmosis lab

21. Osmosis Grape Lab Percent Change = Day 2 – Day 1 Mass x 100 Day 1 Mass

22. Quiz Paramecium live in freshwater. They have a 3% salt internal environment. How do they keep from exploding in this hypotonic environment? Contractile Vacuoles – Organelles found in unicellular organisms that collect, then pump out excess water that enters through osmosis. Does require energy. Like a sump pump in your basement!

24. Contractile Vacuoles

25. Facilitated diffusion Diffusion with assistance from Carrier proteins. Can’t occur fast enough on their own or too large to pass through pores. May occur into or out of cell. Carrier proteins are specific to 1 type of molecule. Animation

27. Steps in Facilitated Diffusion: 1. Carrier protein binds to molecule to be transported. 2. Carrier protein changes shape (shielding it from hydrophobic interior of bilipid layer). 3. Carrier protein releases molecule & goes back to its original shape. Occurs with glucose & amino acids (that can’t pass through cell on their own).

28. Diffusion thru Ion Channels – Na+, K+, Ca2+, & Cl- cannot pass thru the membrane. Ions can not pass since ions aren’t soluble in lipids. Therefore, they need ion channels to provide a small passageway for each ion. Conditions for ion channel gates to open. 1. Stretching of cell membrane 2. Electrical signals 3. Chemicals in cytosol or external environment.

29. Active Transport • Movement of molecules from [Low] to [High]. Energy is needed • Cell Membrane Pumps • Use Carrier Proteins and becomes cell membrane pumps • Sodium – Potassium pump - Transports Na+ and K+ up [ ] gradient • 3 Na+ from cytosol bind to the carrier protein • Carrier proteins breaks ATP to ADP + P, P group binds to Carrier protein • 3 Na+ are released to environment. Carrier protein changes shape. • 2 K+ from outside cell bind to Carrier protein • With release ofPgroup, K+ ions released into cytosol • Cycle repeats • Top speed – 450 Na+ & 300 K+ per second • Inside of cell membrane is now negatively charged, outside is positive. Difference is necessary for electrical impulses along nerve cells. • McGraw Hill video

31. Endocytosis and Exocytosis Engulfing of macromolecules & food particles into the cell membrane Animation 1 Animation 2

32. Endocytosis – Cells ingest external fluids, macromolecules & large particles. • Cell membrane surrounds material into a pouch. • Cell membrane around pouch pinches together to form a vesicle. • Vesicle may fuse with lysosome for digestion

33. 2 Types of Endocytosis • Pinocytosis (cell drinking) if solutes or fluids are involved • Phagocytosis (cell eating) if large particles or whole cells are involved Another animation Occurs with bacteria, viruses or phagocytes (WBC)

34. Exocytosis – Release of vesicles thru cell membrane. May be proteins, waste materials, or indigestibles. • Vesicles fuse with membrane, release contents into environment • Proteins packaged by Golgi Apparatus into vesicles which fuse with membrane to release excess proteins • Animation

35. Vocabulary • Carrier protein Diffusion • Hypotonic Passive transport • Concentration gradient Equilibrium • Ion channel Plasmolysis • Contractile vacuole Facilitated Diffusion • Isotonic Turgor pressure • Cytolysis Hypertonic • Osmosis Active transport • Phagocytosis Sodium – K pump • Vesicle • Endocytosis Exocytosis • Pinocytosis Phagocytosis