1. Discuss why the sugar residues of glycoproteins and glycolipids are located only on the outside face of the plasma membrane and how these residues are involved in cellular recognition.
2. Examine scanning electron micrographs of freeze-fractured plasma membrane, and determine which face is the cytoplasmic and which the external side of the membrane (the proteins are more frequent in the cytoplasmic face). Discuss why that would be so.
3. Consider why a lipid bilayer is referred to as a ``two-dimensional fluid.'' Talk about why proteins and phospholipids are able to move about freely in two layers but why they are very unlikely to switch from one face of the bilayer to the other.
4. Discuss the function of cholesterol in the plasma membranes of animal cells, and consider why it is missing in plant cells. (There are other lipids that serve the same function in plant membranes.)
5. Discuss the different kinds of proteins that are located in and attached to the plasma membrane, and consider their different functions. Note that these membrane-associated proteins are also found in membrane-bounded organelles such as vesicles, vacuoles, mitochondria, and chloroplasts. Consider how they function there as compared with their function in the plasma membrane.
6. Use dialysis bags containing different molar solutions of saline, and place them in different molar solutions in beakers at the start of class for examination at the end of class. Then determine which beakers represent a cell in a hypotonic, hypertonic, or isotonic solutions.
7. Consider the functions of the different kinds
of junctions that hold cells together and what kinds of cells
they would be likely to link.