Lab 1
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BIOLOGY 151

Laboratory Principles of Biology —Fall 2003

Lab dates                  

(week of)                    Lab                 Topic 

Sept. 1                        1.         Introduction to the Way Biologists Work


Sept. 8                        2.         The Scientific Method 

Sept. 15                     3.         Forest Ecology:  Community Structure and Sampling Field Work* 

Sept. 22                     4.         Forest Ecology:  Community Structure and Sampling 

Sept. 29                     5.         Interactions Among Organisms 

Oct. 6                          6.         Natural Selection and Gene Frequencies 

Oct. 13                     Fall Break and Laboratory Practical Test l (Labs 1-6)

                                (JV will take the test on Oct. 15 at 3:00 pm; KW on Oct. 16

                                 at 3:00 pm; conflicts will be resolved with individual

                                 students.) 

Oct. 20                        7.         The Cell Cycle and Cell Division 

Oct. 27                        8.         DNA Fingerprinting 

Nov. 3                         9.         The Kingdoms of Monera and Protista 

Nov. 10                       10.       Plant Structure and Evolution 

Nov. 17                       11.       Animal Body Plans 

Nov. 24                       Thanksgiving Break, NO LABS this week. 

Dec. 1                        Laboratory Practical Test ll (Labs 7-11) 

All laboratory sections will meet in Gilmer 124, 1:30—4:00 P.M. 

*This lab will be outdoors.  Please dress appropriately.

 

 

LABORATORY ONE

 

            INTRODUCTION TO THE WAY BIOLOGISTS WORK

            To begin our semester of laboratory, we will focus on the way biologists go about their work.  Scientists use technology extensively in their activities, and for biologists one essential piece of technology is the compound light microscope.  Our work today will focus on learning to use this powerful tool properly.  We will also learn to use the stereoscopic or dissection microscope.  In the final minutes of today's laboratory, you will begin planning how to use the microscope to investigate a simple problem.  Biologists (and scientists generally) have an orderly way of investigating nature called the scientific method.  You will understand the process of science better by looking at components of this method and by actually doing some of the steps. You will begin a scientific inquiry today and continue with that work next week by actually designing and executing a simple experiment. 

 

THE COMPOUND LIGHT MICROSCOPE

            Our discussion of the compound light microscope includes:  (1) a review of the parts of the instrument, and (2) some experience with prepared slides and wet-mount slides.  Rules for using the microscopes are numbered and presented in bold type and are embedded within the procedures.   These rules apply to our specific laboratory setting and to our scopes, but most of the rules are very appropriate for microscope use in any setting.  Notice, too, that important words are in bold-face type.

Rule 1.  You will be assigned a particular microscope that you will use each time you need to use a microscope in a laboratory exercise.  Always use your assigned microscope.  Always use two hands when carrying the microscope to and from its storage compartment and your lab desk.

 

Rule 2.  Clean the lenses of the microscope with lens paper before and after using it.   Use only approved lens paper and cleaning solutions to clean lenses.  Note: Kimwipes and paper towels will scratch the lenses.

 

A.  Parts of the Microscope

            The compound light microscope that we will use in this laboratory is the Nikon binocular laboratory microscope.  (See Figure 1.)  Our microscope has a built-in light source.  Locate the light switch on the base of the microscope.  Notice that the intensity of the light can be adjusted here.  Review the parts of the microscope and their functions that are listed below by finding the part on your assigned microscope.

 

            • Oculars (eyepieces or ocular lenses)—These are the lenses through which you view the magnified image.  You can adjust the distance between the oculars to fit the distance between your eyes.  The magnification capability of the oculars is 10X (or ten times).  In the right ocular there is a pointer that should help you to indicate some specific detail of interest to a fellow student or to the instructor.

 

 

 

 

Rule 3.  Leave the ocular lenses in place on the microscope.

 

bulletRevolving Nosepiece – This part enables you to change magnification of the image.  The various objectives are mounted on this wheel and can be snapped into place for viewing at the different magnifications.

 

 

 

 

 

 

                       

Parts of the Nikon Microscope

 

 

 

Nikon Microscope

Fig.1
• Objectives (objective lenses)—Attached to the revolving nosepiece are four objectives. The magnification of the objectives is printed on the casing of each.  The shortest objective is the scanning or 4X objective.  The next longest is the 10X objective or low power.  The next longest is 40X or high-power objective, and the longest objective is the 100X objective or the oil-immersion objective.  We will not use the 100X objective today or routinely, and we will learn about its proper use later.  When this objective is used, immersion oil is placed on the slide with the tip of the objective resting in the oil to reduce the refraction of the light.

            Remember that we have called this Nikon a compound microscope.  This word "compound" refers to the fact that there are several lenses involved in making the image that you see.  In fact, there are enough lenses involved that the image viewed is upside down and backwards relative to the actual specimen.

 

            • Stage—This is the flat surface on which the slide is placed.  Notice the aperture (opening) on the stage through which light passes.  Our microscopes are equipped with clips for holding the slide and control knobs for moving the slide into different positions.  This device is referred to as a mechanical stage.

 

                • Condenser—Underneath the stage is the condenser, a set of lenses that focuses the light.  The condenser has a control knob that allows for its adjustment.  Normally the condenser should be up as high as it will go towards the stage.  The iris diaphragm at the top of the condenser controls the amount of light that is delivered through the aperture of the stage.  The diaphragm is adjusted by a lever or a wheel on our Nikon microscopes.  You can adjust the light coming through the microscope in the following ways:  by turning the light switch or by adjusting the iris diaphragm.  Higher magnifications usually require more light.

 

            • Focal Adjustment Knobs—Focusing the image is accomplished by using the coarse adjustment knob (the larger wheel) with the scanning and low power objectives.  The fine adjustment knob (the smaller wheel) is used with the high-power objective and with the oil immersion objective if it is used.

 

Rule 4.  Never use the coarse adjustment knob when focusing with the high-power or oil immersion objectives in place as this can damage the objective or the slide.

 

B.  Using the Microscope

 

1.         Place a slide of colored thread on your microscope stage.  Center the crossed threads over the aperture.  Turn the revolving nosepiece so that the scanning objective is in place.  While looking from the side, turn the coarse adjustment knob until the scanning objective is as close to the slide as it will go.  Now, looking in the oculars, turn the coarse adjustment knob until the image of the crossed threads comes clearly into the field of view (the circle of light that you see when looking through the oculars).  The magnification of the image of the crossed threads is 

determined by multiplying the magnifying power of the oculars (in this case, 10) times the magnifying power of the objective (in this case, 4).  Therefore, the overall magnification is 40X.  The following magnifications are obtained with our microscopes:

 

 

 

scanning objective (4X) times 10X ocular = 40X magnification

low-power objective (10X) times 10X ocular = 100X magnification

high-power objective (40X) times 10X ocular = 400X magnification

oil-immersion objective (100X) times 10X ocular = 1000X magnification

 

2.         With the crossed threads in sharp focus with the scanning objective in place, turn the revolving nosepiece so that the low-power objective is in place.  You should now have to focus very little, if at all, in order to have the image in sharp focus.  This property of being able to change objectives with little focusing is called parfocal capability.  A microscope that can do this is said to be parfocal.  Only good quality microscopes, such as our Nikons, have this capability.

            At this power, with the image at 100X magnification, determine which thread is on top of the other two.  Using the coarse adjustment knob, make the image go in and out of focus and determine which colored thread's edge comes into focus first with the other threads as background.  Have your instructor check your choice.  What you have demonstrated for yourself by doing this is that you can detect depth with the microscope.  The portion of the specimen on the slide that is in focus at any moment is in the focal plane of the lens system being used.  The focal plane has some thickness, and that thickness is known as the depth of field.  High-power lenses have shallower depths of field than do low-power lenses.

 

3.         Look at the distance between the tip of the low-power objective and the slide. With the image in clear focus on low-power,  turn the high-power objective in place.  Now look at the distance between the tip of this objective and the slide. The distance between the tip of the objective and the slide is called the working distance.  Note that the greater the magnification of the objective, the smaller the working distance.  It is important to remember the small working distances of high power objectives so that you will not damage microscopes or slides.  Use the fine-focus adjustment knob to explore the shallow depth of field at high power.

 

4.         Turn the revolving nosepiece so that the scanning or low-power objective is in place, and

remove the thread slide from your microscope.

 

Rule 5.  Remove slides from the microscope only with the low-power or scanning objectives in place.  Never remove a slide with the high-power or oil immersion objective in place as you might scrape the lens of the objective.

 

5.         Place a slide of diatoms, microscopic organisms from both marine and fresh water environments, on your microscope.  With the scanning objective in place, look at the circle of light with the very small algal cells scattered about.  Find a group to look at and center this group in the field of view by moving the mechanical stage.

 

6.         Sketch 3 or 4 diatoms.

 

7.         Turn the low-power objective into place, and examine the chosen group at the higher magnification.  The field of view here has fewer diatoms but larger images. 


 

 

8.         Sketch one or two diatoms from step 6 in more detail.  The diameter of this field of view is about 1600 micrometers.  A micrometer is 1/1000th of a millimeter.

 

9.         Find a particular diatom to look at, center it in the field of view, and switch to high-power.  The diameter of this field of view is estimated to be about 400 micrometers.  By comparing a dimension of your chosen diatom, its length or width, to the diameter of the field of view, you can estimate the size of your diatom in micrometers.  Suppose that your diatom covers about half of the field of view; then the estimate of its length will be 200 micrometers (400 micrometers of the field of view diameter divided by 2, because two of these diatoms would fit across the whole field).

 

10.       Estimate the size of several diatoms that you sketched and record their dimensions.  Check with others in the laboratory to see if they agree with your estimates.

           

11.       Turn the low-power or scanning objective into place and remove the diatom slide from your scope.

12.       Not all of the slides that you will use in this laboratory will be prepared slides.  Some fresh or live material is best viewed with the microscope using a wet-mount slide.  Watch as your instructor demonstrates how to make a wet-mount slide.

 

13.       With a dropper, place a small amount of water on a clean slide.  Place a leaf of the water plant Elodea on the slide in the drop of water.  Place the edge of a cover slip at the edge of the drop and lower the cover slip slowly to the slide surface.  With care you can prepare a wet-mount with few if any air bubbles.

 

14.       Observe your wet-mount preparation at scanning, low, and high power.  Sketch what you observe and note any movement or interesting features.  Observations that you make now may help you with next week’s experiments.

 

15.       On the back lab bench, locate the stereoscopic or dissection microscope.  With this microscope, look at the objects that are available.  Objects best viewed with a dissection microscope are much larger than those viewed with a compound microscope and do not require the same preparation.  Notice that the image here is clearly three-dimensional and is not inverted or reversed as with the compound scope.

 

Assignment:

 

Read Laboratory Two and read the essay Pilgrim at Tinker Creek by Annie Dillard that is available to you in the laboratory.  Identify observations in the essay that might lead to scientific questions that could be investigated through experimentation. Write out at least two observations and propose experiments that might help you to answer questions that are suggested by these observations.  Present your work in good form in a word-processed document, which will be collected at the beginning of next week’s lab.

 

 

 

NOTES: