Cells take in nutrients and expel waste through their membranes using two main processes: passive transport and active transport. Passive transport moves substances across membranes without cell energy expenditure, including diffusion, osmosis, and facilitated diffusion using carrier proteins or ion channels. Active transport requires cell energy in the form of ATP to pump substances against their concentration gradient, as seen with the sodium-potassium pump. Endocytosis and exocytosis use vesicles to transport larger molecules into and out of cells. Membrane receptor proteins also allow cells to communicate.

1. Chapter 4 Notes Cells and Their Environment

2. Molecules need to move across membranes in cells… IN food carbohydrates sugars, proteins amino acids lipids salts, O2, H2O OUT waste ammonia salts CO2 H2O products How does that happen? Image modiified from: http://www.accessexcellence.org/AB/GG/importProt.html

3. I. Passive Transport Passive Transport-the movement of substances across the cell membrane without the use of energy by the cell. There are many types of passive transport:

4. A. Diffusion Diffusion- is the movement of a substance from an area of high concentration to an area of low concentration. Diffusion will eventually cause substances to be balanced (equilibrium) on both sides of the cell membrane. Ex: ink or food coloring moving through water.

5. Diffusion-high to low concentration. Animatioin from: http://www.biologycorner.com/resources/diffusion-animated.gif

6. B. Osmosis Osmosis- is the diffusion of watermolecules across a selectively permeable membrane. (Egg Experiment)

8. 1. Hypotonic-solute outside cell less than inside; water moves into cell; cell swells 2. Hypertonic-solute outside cell greater than inside; water moves out of cell; cell shrinks 3. Isotonic-solute outside cell equals inside; no net movement of water.

10. C.Facilitated Diffusion Facilitated Diffusion-when a membrane protein helps to transport a substance across a cell membrane.

11. Types of Facilitated Diffusion 1. Ion Channels-proteins that have a pore through which ions such as sodium, calcium,potassium can cross the cell membrane. Animation from: http://www2.uic.edu/~myilma1/ionchannel.gif

12. Types of FacilitatedDiffusion 2. Carrier protein-proteins that bind to specific substances, carry it across the cellmembrane, and release it. Animation from: http://bio.winona.edu/berg/ANIMTNS/facdifan.gif

13. II. Active Transport Active Transport-the movement of a substance into an area of higherconcentration by using energy from the cell in the form of ATP. There are many types of active transport:

14. 1. Sodium-Potassium pump sodium ions are pumped out of the cell. Potassium ions are pumped into the cell. http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/eustruct/images/sppump.gif

15. 2. Endocytosis-substances that are too large to move into the cell membrane are moved by a vesicle that forms around it. http://www.accs.net/users/kriel/chapter%20nine/ Animation from: http://academic.brooklyn.cuny.edu/biology/bio4fv/page/cell-movement.html

16. 3. Exocytosis-substances that are too large to move out of the cell membrane are released by a vesicle that forms around it.

17. 4. Membrane Receptor Proteins-proteins that help cell communicate with each other. http://academic.brooklyn.cuny.edu/biology/bio4fv/page/rectpr.htm