The diatoms below are magnified 400x. To find the total magnification while looking under a microscope, you must multiply the power of the eyepiece lens by the power of the ? *

ll living things are composed of cells. This is one of the tenets of the Cell Theory, a basic theory of biology. This remarkable fact was first discovered some 300 years ago and continues to be a source of wonder and research today. Cell biology is an extremely active area of study and helps us answer such fundamental questions as how organisms function. Through an understanding of how cells function we can discover how human ailments, such as cancer and AIDS, can be possibly treated.

THE CELL THEORY

All life is composed of cells

Cells are the fundamental units which possess all the characteristics of living things

New cells can only come into existence by the division of previously existing cells

Notice that this scientific concept about life is called a theory. In science, unlike the layman’s definition, the word theory is used for a hypothesis about which there is a large body of convincing evidence. Under experimental conditions all observations have thus far confirmed the theory. The evidence that helped formulate the theory was obtained using the microscope. The microscope is of enormous importance to biology and has extended our ability to see beyond the scope of the naked eye.

When we look at cells under the microscope, our usual measurements fail to work. In science, the metric system is used to measure objects and, as you will see, is vastly superior to our antiquated English system of measurement. Here are the basic units:

LengthVolumeWeight

1 meter (m)1 liter (L)1 gram (g)

1 millimeter (mm) = 0.001 m or 10−3 m or 1/1,000 m1 milliliter (ml) = 0.001 L or 10−3 L1 milligram (mg) = 0.001 g or 10−3 g

1 micrometer (mm)= 0.000001 m or 10−6 m or 1/1,000,000 m1 microliter (ml) = 0.000001 L or 10−6 L1 microgram (mg) = 0.000001 g or 10−6 g

1 nanometer (nm)= 0.000000001 m or 10−9 m or 1/1,000,000,000 m  

There is also a different scale for temperature: Celcius.

100˚ Celcius (C) = water boiling (equivalent to 212˚ F)

0˚ C = water freezing (equivalent to 32˚ F)

Converting between units can be confusing. The most effective way to do this is by using conversion factors and canceling units. For example, if you want to know how many liters are in 425 milliliters, you can set up a simple equation that looks like this.

[latex]\displaystyle{425}\text{ ml}\times\frac{1\text{ liter}}{1000\text{ ml}}=\frac{425\text{ ml}}{1000\text{ ml}}=0.425\text{ L}[/latex]

PRACTICE

1.2 mm = mm0.224 m = mm225 nm =mm

0.023 L = ml750 ml = L50 ml       = L

Part 1: Microscope Parts

Nikon microscope with parts labelled. The compound microscope is a precision instrument. Treat it with respect. When carrying it, always use two hands, one on the base and one on the neck.

The microscope consists of a stand (base + neck), on which is mounted the stage (for holding microscope slides) and lenses. The lens that you look through is the ocular (paired in binocular scopes); the lens that focuses on the specimen is the objective.

Your microscope has four objectives of varying magnifications (4x, 10x, 40x, and 100x) mounted on a revolving nosepiece. The 100x objective is a special oil immersion objective that needs to be used with oil—we won’t use the oil immersion objective for this course.

Positioning the specimen requires that you turn the mechanical stage controls, which operate the slide bracket on the surface of the stage. One control moves the specimen in the x-direction, and the other moves the specimen in the y-direction.

Focusing on the specimen is achieved by knobs that move the stage up and down, so that it is closer or farther from the objective. There are two knobs, an outer coarse focus and an inner fine focus.

The substage condenser directs light through the slide into the objective. An iris diaphragm on the substage condenser controls the amount of light reaching the objective, and also affects the contrast of the specimen.

Part 2: Magnification

The compound microscope has two sets of lenses; the ocular lens (or eye piece) which magnifies an object 10 times its normal size, and the objective lenses located on a revolving nosepiece. Rotate the nosepiece and notice how each objective lens clicks into place. Each objective lens has a different magnification of power written on it (such as 4, 10, 40, or 100). This number is the power of magnification for each of the objective lenses. For total magnification multiply the ocular power (10x) times the objective lens that is in place. For example, if you have a 10x ocular and a 10x objective, the total magnification is: 10x × 10x = 100x.

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