What is a concentration gradient?

1. What is a concentration gradient? The difference between the concentration of a substance on either side of a membrane.

2. Describe the process of diffusion and explain why it occurs Diffusion involves random movement of ions or molecules from a region of higher concentration to regions with lower concentration. It occurs because all molecules are in motion. http://edmundgwi2020.blogspot.ca/2011/12/equilibrium-in-life.html

3. What are three factors that affect the rate of diffusion and why do they affect it? Temperature, pressure, molecular size, polarity. An increase of temperature or pressure increases the rate of diffusion and makes molecules move faster Rate of diffusion is inversely related to molecular size – the larger the molecule the more difficult it is to diffuse across a membrane Small polar molecules generally have lower rates than non-polar molecules of the same size In general charged molecules and ions cannot diffuse across a cell membrane.

4. Explain the similarities and differences between diffusion and osmosis Both involve random movement of results in a net change from higher to lower concentration. Osmosis refers only to diffusion of water molecules across a selectively permeable membrane. http://deltabiology.com/2012/diffusion-vs-osmosis/

5. Would you expect the normal environment of your cells to typically be isotonic, hypertonic, or hypotonic? Explain your reasoning. Isotonic – since they are normally not crenated (shrunken;hypertonic) or swollen (hypotonic) http://www.fashion-res.com/isotonic-hypotonic-hypertonic-iv-solutions/

6. Would you expect the normal environment of a plant cell to be typically isotonic, hypertonic, or hypotonic? Explain your reasoning. Hypotonic since this condition fills the central vacuole with water, providing rigidity (turgor to the plant, which is required to keep it upright). http://www.citruscollege.edu/lc/archive/biology/Pages/Chapter04-Rabitoy.aspx

7. What do facilitated diffusion and active transport have in common, and how do they differ? Both use membrane proteins and aid in the movement of molecules across a membrane. Facilitated diffusion moves molecules down their gradients (with their gradients) and does not require energy. Active transport requires net input of energy to move substances against their gradients. http://hyperphysics.phy-astr.gsu.edu/hbase/biology/actran.html

8. Compare and contrast a channel protein and a carrier protein Both are integral membrane proteins used to transport molecules across a membrane. Carrier proteins bind the molecules they transport, changing their shape and move solutes slowly. Since channel proteins do not bind molecules they allow high rates of diffusion.

9. What is ATP, and what role does it play in active transport? ATP is a nucleotide with three phosphate groups. The hydrolysis of ATP provides the energy to move a substance against its concentration gradient. http://medical-dictionary.thefreedictionary.com/active+transport

10. How is an electrochemical gradient similar to and different from a concentration gradient? An electrochemical gradient involves two differences across a membrane – a concentration difference and an electric potential difference.

11. Distinguish between primary and active transport and secondary active transport. PAT – ATP hydrolysis is used directly by a transport protein as a source of energy for transporting a substance across a membrane against a gradient. SAT – energy from ATP is used indirectly to power the transport against its gradient. PAT of a different process supports of a gradient that the secondary active transporter uses to power its transport process. http://oregonstate.edu/instruction/bb350/textmaterials/ch08.html

12. What is the sodium-potassium pump, and how does it work?

13. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html Click here…

14. What is the sodium-potassium pump, and how does it work? • It is a primary active transporter that hydrolyzes one molecule of ATP for every 3 sodium ions it pumps out of the cell. • It then pumps 2 potassium ions into the cell. • Both ions are moved against their concentration gradient. • ATP hydrolysis changes the shape of the protein allowing for the pumps actions. • The first confirmation (from the hydrolysis of ATP) allows for the binding of NA++ and the movement across the gradient. The release of the phosphate group allows for the binding of K+ ions and return to its natural confirmation, bringing the K+ ions back into the cell.