Lewis/Life - Teaching Techniques

Chapter 5 - Teaching Techniques

A. General Tips
This chapter includes a great deal of information, much of it totally new to your students. Be aware of what your class objectives are and also be aware of the backgrounds of your students. The concepts presented in this chapter are logical and sequential, but students with weak backgrounds can easily become overwhelmed by the terminology. If necessary, streamline this material to meet the needs of your class. A conceptual understanding of what is happening with the cell is essential for many of the ideas presented later in the book and is far more important than a regurgitation of definitions.
B. Possible Approaches to the Chapter
Consider starting this chapter with this three question non-quiz: Why are transplanted organs sometimes rejected? Why is it necessary for substances to get in and out of cells? Look at your arm; how do the cells "stick together?"
Students have usually never thought about why transplanted organs are rejected and most will not have a solid answer to that question. The second question will cause the students to stop and think but most will arrive at a correct answer. The third question will baffle those who have never studied this material before.
You now have a lead in for the material covered in this chapter. Since there is so much new material, I suggest that you cluster terms and make charts, such as Tables 5.1, 5.2, and 5.3. Other possible cluster charts could include the names of the proteins listed in this chapter.
C. Hints Related to Specific Chapter Topics
II. Use Figure 5.3 (or a similar drawing) as a pivot point for discussions on cells membranes, diffusion, osmosis, and active transport. Relate this figure to Figures 5.11 and 5.12.
Relate Figure 5.13 to Figure 5.14.
III.A. Probably the most important rule you can impart to your students about diffusion is that everything tends toward equilibrium. If they can remember that, they will not have any trouble with any diffusion (or osmosis) problem you present them with.
III.B.1. There are several desktop experiments that can be performed to help explain movement across cell membranes. An extremely effective way to demonstrate tonicity involves two uncooked eggs with unbroken shells, corn syrup, vinegar, and two beakers. (Variations of this experiment are often found in introductory biology lab books, but the experiment can be done equally well in the lecture hall.)
Several days before your discussion on tonicity, bring in the above mentioned materials. Have the students note the size of the eggs. You can certainly weigh and measure the eggs but this experiment is just as effective without exact measurements. Place one egg in each beaker. Fill one beaker with corn syrup and the other beaker with vinegar. Be sure the students notice the fizz forming around the egg in the vinegar.
During the next class period, remove the eggs. Tap the one from the syrup so the students notice that it is hard (shell in tact). Try not to disrupt this egg because you want the syrup to remain on the egg.
The students should notice that the egg from the vinegar beaker has no hard shell and that it is considerably larger than it was. Pass it around the room. Tell the students that the vinegar is about 5% acetic acid (and 95% water). Now put the egg from the vinegar in the syrup and the egg from the syrup in the vinegar. Note the consistency of the syrup.
During the next class period, everyone should notice that the egg that had originally expanded in the vinegar had now shriveled in the syrup and the syrup had become quite watery. If everyone was careful, the original syrup egg should still have its shell, even in the vinegar.
A chemical reaction occurred between the vinegar and the shell. When the shell was gone, the egg was surrounded by a selectively permeable membrane and osmosis occurred. Water entered the egg -- toward equilibrium. When the egg was placed in the syrup, which had a higher particulate concentration than the egg, water left the egg by osmosis and the syrup became watery. This was again toward equilibrium.
III.B.2. To demonstrate turgor pressure (p. 90), bring in a wilted lettuce leaf and a dish of water. Put the leaf in the water at the beginning of class and examine it at the end.
II.A. Often the phospholipid part of the phospholipid bilayer is difficult for students to visualize -- even given such drawings as Figure 5.3. Refer back to Figure 3.19. Sketch this figure either on the board or on the overhead. Then remove one of the fatty acid chains and replace it with a phosphate group. Explain that the triglyceride has become a phospholipid. Now, draw a ring around the phosphate group and the glycerol back bone and tell the students that this ringed area is represented by the ball in the phospholipid bilayer and that the two fatty acid chains are represented by the two tails hanging from the ball in the diagram -- such as Figure 5.3.
VI. This entire section on the cytoskeleton can be assigned for completion outside of class time. Ask the students to write to hand in a detailed outline covering this material.