1) The integrity of the plasma membrane is essential for cellular survival. Could the immune system utilize this fact to destroy foreign cells that have invaded the body? How might cells of the immune system disrupt membranes of foreign cells? (Two hints: virtually all cells can secrete proteins, and some proteins form pores in membranes.)

2) Most cells are very small. What physical and metabolic constraints limit cell size? What problems would an enormous cell encounter? What adaptations might help a very large cell to survive?

3) Some species of bacteria that live at the surface of sediment on the bottom of lakes are facultative anaerobes; that is, they are capable of either aerobic or anaerobic respiration. How will their metabolism change during the summer when the deep water becomes anoxic (deoxygenated)? If the bacteria continue to grow at the same rate, will glycolysis increase, decrease, or remain the same after the lake becomes anoxic? Explain why.