2. The cell membrane is sometimes referred to as a "lipid bilayer." Explain the rationale for this term.
3. The cell membrane is selectively permeable. What does this term mean? How is it important to the functioning of the cell?
4. Cell membranes are fluid mosaics. How do membranes remain fluid? What macromolecules are embedded in membranes to form the "mosaic" and what functions do they serve?
5. What is diffusion? What is osmosis? How are the two different?
6. What is osmolarity?
7. Three important mechanisms for transporting substances across cell membranes are simple diffusion, facilitated diffusion, and active transport. Which of these transport mechanisms requires a protein channel to transport the substance? Which requires a concentration gradient to move the substance? Which requires energy? Which can move a substance against a concentration gradient? What properties determine whether a substance can cross the membrane unaided or whether it requires a protein carrier?
8. Suppose we construct an artificial cell surrounded by a strong semi-permeable "membrane" through which only water can pass. On the inside of the cell we place a 5% glucose solution. What would happen to the cell when placed in each of the following solutions?
a. distilled waterb. 5% Na+ solution
c. 10% Na+ solution
9. Assume we start with the same artificial cell with 5% glucose solution inside. This time, however, presume that we have built into the semi-permeable membrane many Na+ channels so that sodium ions can pass through the membrane. Describe how the cell would differ from the start AT EQUILIBRIUM in each of the solutions above.
10. How do exocytosis and endocytosis differ from the transport mechanisms in the above question?
11. As science officer aboard the USS Enterprise, you beam down to the planet Krisko to explore its life forms. Organisms on this planet, like those on earth, are composed of carbohydrates, lipids, proteins, and nucleic acids and cells are surrounded by membranes composed of phospholipids However, on Krisko, lipids are the solvent in which all biological reactions occur (on earth the solvent is water).
Given these conditions, how will the phospholipids in the membranes be arranged so as to form a selectively permeable membrane? DRAW a diagram and EXPLAIN your reasoning. (Don't worry about the transport proteins.)
12. Identify and label the designated structures in the diagrams. Be familiar with the appearance and function of each of the organelles. Which are surrounded by membranes? Why is it important for organelles to have membranes?
nucleus
rough endoplasmic reticulum (ER)
chloroplast
smooth ER
Golgi apparatus
lysosome
central vacuole
vesicle (for transport)
mitochondrion
ribosomes
13. What are the functions of the cytoskeleton? What are the three main types of fibers that make up the cytoskeleton?
14. Describe the function of each of the following intercellular junctions:
tight junctionsgap junctions
desmosomes
plasmodesmata
15. How do animal and plant cells differ? How are these differences important to the functions each cell type must perform?
16. How do eukaryotic and prokaryotic cells differ? Which of the structures listed in question #12 are found in each kind of cell?
17. How does the abundance of certain organelles and structures specialize a cell for a particular function?
18. Assume you find a cell with an abundance of mitochondria. What might you suspect about the function of that cell? What about a cell with a highly folded surface?
19. Consider the following cell. Label the indicated organelles. What organelles are in abundance? What process is the cell carrying out at the top? What do you think is the function of this cell?
