Answer Key: Exercise 2
THEMICROSCOPE
Page 17,Box 2.1 Calculating Total Magnification for the Microscope
Objective lens / 4 / 10 / 40 / 100
Ocular lens / 10 / 10 / 10 / 10
Total magnification / 40 / 100 / 400 / 1000
Note: Magnification on objective lenses may vary. For example, some high or high-dry objective lens are 43x or 45x.
Page 19–20, Focusing with the Microscope
1. The letter "e" as viewed through the microscope should look inverted compared to its naked eye appearance on the stage.
2. The light is best adjusted using the iris diaphragm.
3. Streaks and blurs are usually due to being in the wrong plane of focus. You may really be seeing microscopic scratches in the glass of the microscope slide, or seeing dirt particles which are difficult to focus.
Page 21, Focusing with the Microscope
1. The ink should have been most uniform when using the scanning power (40x TM).
2. They would be most blotchy when using high power (400x TM).
3. Scanning power (40x TM) provides the clearest image.
4. Yes, the orientation was the same at all powers.
5. It should have been necessary to reduce the light at first using the scanning power. As you switched to higher power lenses, it should have been necessary to increase the amount of light with the iris diaphragm.
Page 21, Determining Depth of Focus
1. The scanning power (40x TM) lens should have been most effective.
2. The high power (400x TM) lens has a much more limited depth of focus than lower powers.
3. The high power lens would have always had no more than one thread at a time in focus.
4. This answer is dependent on the slide actually used in your lab.
5. Since it is difficult to have more than one or two threads in focus at once, recalling their order from top to bottom as you focus can be difficult.
Page 22, Appling Magnification and Field Size to Biology
Part 1. Whitefish Blastula
The 40x objective lens (400x total magnification) should be necessary to truly see the details inside cells.
Part 2. Ox Spinal Cord.
No, the spinal cord is a little too large to see the entire specimen even under the lowest power magnification. However, when you move it around you should be able to form a mental picture similar to 11.5.
Page 23–24, Preparing a Wet Mount Slide
1. An individual cheek cell is somewhat irregular when viewed from the top, but may look somewhat circular overall.
2. Cheek cells are thin.
3. A thin cell may allow your body to pile many layers of cells into a small area (or a thin layer). This can be useful for protection from friction.
4. The nucleus was mostly centrally located.
5. When spread out, one would see only one layer.
6. Cheek cells normally contain many layers of flat cells to protect the cheek from friction.
7. Cheek cells connect using special structures embedded in their membranes that you will learn about the Cells section of the course.
Answers to Review Questions:
1. Match the part of the microscope to the description on the right.
e Condenser
c Coarse-adjustment knob
a Stage controls
b Fine-adjustment knob
d Objective lenses
2. What is the total magnification if the ocular lens is 10x, and the objective lens is 100x? Show the calculations.
10 x 100 = 1000 TM
3. Why should you scan a specimen under scanning power before using higher magnifications?
Lower magnifications allow you to see a greater area of your slide. They also allow you to focus your specimen more easily, and the scanning power allows you to quickly find your focus using the coarse-adjustment focusing knob.
4. After focusing on the top of the specimen, what happens to the depth of focus as you turn the fine adjustment knob backward?
The depth of focus is fairly thin (and gets progressively thinner as you increase magnification). It is almost impossible to keep the top and bottom of thicker specimens completely focused at the same time. This is part of the reason why specimens prepared for microscopic viewing are either already very thin (e.g. single-celled organisms) or are sliced thin. For thicker objects you need to focus up and down to create a mental picture.
5. How is poor light quality affected by opening the iris diaphragm?
Opening the iris diaphragm simply allows more light to pass through the specimen.
6. Briefly describe how to put away and store your microscope.
Move the nosepiece back to the lowest power objective lens. Wrap the cord as demonstrated by your instructor. Gently place the dust cover over the microscope. Carry the microscope back to its storage area by holding it by the arm and the base.