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Chapter 2
The Metric System and Microscopes
Chapter Outlines
Introduction
Metric System
Microscopes
Light Microscopes
Resolving Power (Resolution)
Parts of the Compound Light Microscope and Their Functions
Electron Microscopes
Review Questions
Introduction
The metric system of measurements, also known as the Systeme International (SI), is the
official system of measurement in nearly every country in the world. All scientists use the metric
system rather than the system that may be most popular in their home country. The French
devised the metric system in 1791 to replace the chaotic collection of units then in use. One of
the goals of this effort was to use the decimal system rather than fractions. The U.S. Metric
Association (USMA), a national non-profit organization founded in 1916, advocates U.S.
conversion to the metric system, known as metrication. The U.S. congress passed a law requiring
all government agencies to use the metric system after 1992. As the government converts to
metric usage, private companies will be required to produce metric products and services. In
addition, by 2015, all European countries will require that imports from the U.S. comply with
their metric standards. The prognosis is that the U.S. will complete metrication very soon, and
the government and private companies will seek employees literate in the metric system.
Two types of microscopes are used in biology: light microscopes and electron
microscopes. There are two types of light microscopes, compound and dissecting; and two types
of electron microscopes, transmission and scanning. Light microscopes use visible light and
glass lenses to detect and magnify small objects, such as cell organelles. The compound light
microscope uses two sets of lenses, ocular lens and objective lens, and magnifies up to 1,000
times. The dissecting light microscope uses a single set of lenses and has a limited magnification
of 40 times or less. However, it gives 3-dimensional images. The compound light microscope
gives only 2-dimenssional images. The electron microscopes use electrons for illumination and
magnetic lenses. The transmission electron microscope (TEM) magnifies up to a million times,
and the scanning electron microscope (SEM) magnifies up to 20,000 times. However, the SEM
gives 3-dimensional images and the TEM gives only 2-dimensional images.
1
Microscopes are used not only for magnification, but also for resolution. The resolution
or resolving power of a microscope is its ability to enable the viewer to distinguish two closely
spaced structures and discern smaller distances between them. Light microscopes are limited by
resolution because they use visible light. Electron microscopes are not limited by resolution
because they use electrons for illumination.
The Metric System
The metric system is the international and scientific system of measurements. Compared
to other local systems of measurements, the metric system has many advantages:
1. The metric system is based on decimals rather than cumbersome fractions.
2. The metric system is coherent and can be manipulated algebraically.
3. The metric units are based on natural standards, such as mass of water and size of earth.
4. Conversions from one unit to another are simplified by multiplying or dividing by 10 or
multiples of 10.
5. The metric system uses base units and prefixes that eliminate use of long rows of zeros.
6. The metric system uses only 30 individual units, compared to hundreds of traditional
units.
7. The metric units are easy to pronounce and write.
8. The metric system is international and used in all countries.
9. The metric system is the standard system of measurement in biology and other sciences.
Commonly used measurements in biology include length (distance), mass (weight), volume
and temperature. Each of these measurements has a base unit to which a prefix is added. The
base units for length, mass, volume and temperature are meter (m), gram (g), liter (L), and
Kelvin (K) or degrees Celsius (0C), respectively. The prefixes commonly used in biology include
deci (d), centi (c), milli (m), micro (µ), and nano (n). The meter has 10 dm, 100 cm, 1,000 mm,
1,000,000 µm, and 1,000,000,000 nm. A kilometer (km) has 1,000 meters. The same prefixes are
used with gram and liter.
The metric units for temperature are the Kelvin and degrees Celsius (0C). Water freezes at
273 K (0 0C) and boils at 373 K (100 0C). The temperature unit in the British system is degrees
Fahrenheit (0F). To convert:
0
C to K
K to 0C
0
C to 0F
0
F to 0C
add 273
subtract 273
(0C x 1.8) + 32
(0F – 32)  1.8
2
Microscopes
Microscopes are used to magnify specimens and to help the viewer see small distances
between small structures. The microscopes commonly used in a biology lab are the light
microscopes. These microscopes use light and glass lenses. They include two types; the
compound light microscope and the dissecting light microscope (stereomicroscope). Other
microscopes used in biology are the transmission electron microscope (TEM) and the scanning
electron microscope (SEM). These microscopes use electrons for illumination and magnetic
lenses.
Light Microscopes
The compound light microscope uses two sets of lenses in series; the ocular lens in the
eyepiece, and the objective lenses on the nosepiece. The ocular lens magnifies 10 times (10X),
and the objective lenses magnify 4, 10, 40 and 100 times. Total magnification is a product of
the magnifications by the ocular lens and the objective lens in use. Possible total magnifications
are 40X, 100X, 400X, or 1000X.
The first lens in a compound microscope is called the objective lens because it’s near the
object being magnified. The objective lens forms the primary image of the specimen, which is
subsequently enlarged with the second lens, called the eyepiece or ocular. The ocular lens forms
the secondary, further-enlarged image.
Each objective lens has a numerical aperture (N.A.), which is an angular measure of the
light-gathering ability and enables the objective lens to resolve fine details. In the compound
light microscope, the values of the numerical aperture (N.A.) are 0.1, 0.25, 0.65, and 1.25 for the
4X, 10X, 40X, and 100X objective lenses, respectively. Magnification and N.A. values are
usually engraved on the body of the objective lens. The compound light microscope is used to
view thin cross sections of specimens, and it produces only 2-D images.
Although the dissecting light microscope (stereomicroscope) gives limited magnification
(about 40X), it gives 3-D images. This is why this microscope is used to view whole objects and
live specimens. This makes it easy to dissect objects, do surgery, or look at complex 3-D objects.
When you look through the eyepiece, you will see a circle of bright light. This is referred
to as the field of view. Using a plastic metric ruler, you can practically measure the diameter of
field of view with the scanning objective lens (4X), and find it to be 4.3 mm or 4,300 µm. It’s
practically not possible to measure the diameter of field of view with the other objective lenses
using this procedure. However, the information obtained by this procedure using the scanning
lens (4X) can be used to calculate the diameters of field of view with the 10X, 40X, and 100X
objective lenses. Multiply the diameter of field of view by the total magnification with the
scanning lens (4,300 X 40) and divide by the total magnification produced by the objective lens
that you want to find its diameter of field of view. This gives the values of 1720, 430, and 172
µm for the 10X, 40X, and 100X objective lenses, respectively.
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As you increase the magnification using the compound light microscope; the diameter of
field of view decreases, the light intensity decreases, the working distance (distance between the
lens and the slide) decreases, and the depth of focus or the depth of field decreases.
Images seen using the compound light microscope appear to be both upside down and
backwards. This is inversion. Also, when you move a slide in any direction, the image you see
appears to move in the opposite direction. This is due to the arrangement of lenses in the
microscope.
Resolving Power (Resolution)
The resolving power (or resolution) of a compound light microscope is its ability to
distinguish two closely spaced structures and discern smaller distances between them. The higher
the effective N.A. value of a microscope, the better is its resolving power. The resolving power
of a light microscope is also dependent on the wavelength of visible light (400 – 700 nm). The
shorter the wavelength of the light used in the microscope, the better is the resolving power. The
resolving power of a light microscope (L.R.) is calculated by dividing the wavelength of light ()
by twice the effective N.A. value of the microscope:
L.R. =   2NA
With the oil immersion lens (100X), the resolving power is about 200 nm. This means that if two
structures in a cell are 200 nm or more apart, they could be seen as two distinct structures.
However, if they are less than 200 nm apart, they will appear overlapped. Since most cellular
structures are less than 200 nm apart, their structural details cannot be distinguished with the
light microscope. This is why resolution is the main limiting factor of light microscopes. This
limitation is due to the nature of visible light. Magnifications of more than 2000X with a light
microscope are called “empty magnifications” because light resolution does not improve with
magnification beyond this limit.
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Parts of the Compound Light Microscope and Their Functions
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The body tube conducts light and holds the eyepiece at the upper end and the revolving
nosepiece at the other end.
The eyepiece contains the ocular lens through which an object is viewed. The
magnifying power of the ocular lens in most microscopes is 10X.
The revolving nosepiece holds the objective lenses, and is rotated to bring each of the
lenses into a viewing position.
The scanning objective lens, with 4X magnifying power, is the shortest objective and
has a black band around it.
The low-power objective lens, with 10X magnifying power, is the middle-sized one and
has a yellow band around it.
The high-power objective lens, with 40X magnifying power, is the third longest one and
has a blue band around it.
The oil-immersion lens, with 100X magnifying power, is the longest one and has a white
band around it. This lens requires a drop of oil between the lens and the slide.
The arm supports the body tube and serves as a carrying handle.
The coarse adjustment knob is the outer, larger focusing knob; used to bring objects
into approximate focus when the scanning and low-power lenses are used.
The fine adjustment knob is the inner, smaller knob and is used to bring objects into
sharp focus. When using the high-power objective lens, only the fine adjustment knob is
used.
The stage and the stage clips hold and support microscope slides. Your microscope uses
mechanical stage. Use stage knobs to move slides up and down, and to the right and to
the left.
The iris diaphragm is attached to the condenser, and it regulates the amount of light
used to view the object.
The condenser focuses light from the light source onto the specimen through an opening
in the stage. Adjustment of the condenser is important for better resolution and contrast.
Ask your instructor to adjust the condenser of the microscope you are using.
The base rests on the bench and contains a built-in substage illuminator and a light
switch.
Electron Microscopes
The fine structures of cells became visible after the discovery of the electron microscopes
in 1953. Electron microscopes are not limited by resolution because they use beams of electrons
and magnetic lenses rather than light and glass lenses. The transmission electron microscope
(TEM) gives high magnification (over a million times) and unlimited resolution. The scanning
electron microscope (SEM) gives much less magnification compared to the TEM, but has the
advantage of producing 3-D images. The SEM produces high resolution images of a sample
surface, and the TEM is used to magnify thin cross sections. Unlike light microscopes, electron
microscopes cannot be used to view processes in living cells.
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Review Questions
Multiple-choice Questions: Select the most appropriate answer of statement
1.
Although the metric system of measurements is used all over the world, in the U. S. we
still use the English system. Scientists all over the world use the metric system rather than
their local systems. The metric system is easy to use because it is based on decimals
rather than fractions and it uses prefixes that eliminate the use of long rows of zeros.
Conversions from one metric unit to another are simplified by multiplying or dividing by
ten or multiples of ten. The metric system is coherent and can be manipulated
algebraically. The use of base units and prefixes makes the metric system even more easy
to use. Which of the following is an advantage of the metric system of measurement over
the English system?
A.
The metric system is the official system of measurement in nearly every
country in the world.
B.
The metric system is based on decimals rather than fractions.
C.
The metric system uses base units and prefixes that eliminate the use of long rows
of zeros
D.
The metric system is coherent, easy to use, and can be manipulated
algebraically
E.
All of these are advantages of the metric system over the English system
Answer: E
2.
Commonly used measurements in biology include length (distance), mass (weight), and
volume. Each of these measurements has a base unit and prefixes added to the base unit.
The base units for length, mass and volume are meter (m), gram (g) and liter (L). The
prefixes placed before each of these base units are deci (d, 1/10), centi (c, 1/100), milli
(m, 1/1000), micro (µ, 1/1000, 000), and nano (n, 1/1000, 000,000). The units of length,
for example, are meter (m), decimeter (dm), centimeter (cm), millimeter (mm),
micrometer (µm) and nanometer (nm). Individual cells of the bacterium E. coli are 5
micrometers (m) long. Express the length of the cells of this bacterium in nanometers
(nm).
A. 5000
B. 50
C. 0.5
D. 0.05
E. 0.005
Answer: A
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3.
The base unit of length (distance) is the meter, abbreviated m. the metric units of length
commonly used in biology are the meter (m), decimeter (dm), centimeter (cm),
millimeter (mm), micrometer (µm), and nanometer (nm). The meter has 10 dm, 100 cm,
1000 mm, 1,000,000 µm, and 1,000,000,000 nm. Another commonly used unit of
distance is the kilometer (km). A kilometer has 1000 m. The thickness of the cell
membrane is 10 nanometers (nm). How many cell membranes can be piled, one on top of
the other, to measure 1 millimeter (mm) in thickness?
A. 100
B. 1,000
C. 10,000
D. 100,000
E. 1,000,000
Answer: D
4.
The length of the door of your classroom is 2.4 meters (m). Express the length of the
classroom door in decimeters (dm).
A. 24
B. 240
C. 2400
D. 24000
E. 240000
Answer: A
5.
The driving distance from Phenix City to Birmingham is 230 kilometers (km). Express
this distance in meters (m).
A.
230,000,000
B.
230,000
C.
23,000
D.
0.023
E.
0.23
Answer: B
6.
If a kilometer (km) is equivalent to 0.62 of a mile, express the distance between Phenix
City and Birmingham in miles.
A.
1.426
B.
142.6
C.
1,426
D.
142,600
E.
142,600,000
Answer: B
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7.
Mass refers to the amount of a substance, while weight refers to the force of gravity
exerted on a substance. The base unit of mass or weight is the gram (g). The metric units
of mass commonly used in biology include gram (g), decigram (dg), centigram (cg),
milligram (mg), microgram (µg), and nanogram (ng). The gram has 10 dg, 100 cg, 1000
mg, 1,000,000 µg, and 1,000,000,000 ng. Another commonly used unit of mass or weight
is the kilogram, abbreviated kg. A kilogram has 1000 g. The nutrition label of a food item
indicates that the amount of sodium (Na+) per serving is 860 milligrams (mg). Express
the amount of sodium in grams (g).
A. 0.00086
B. 0.86
C. 8,600
D. 86,000
E. 860,000
Answer: B
8.
Volume refers to the space occupied by an object. The base unit of volume is the liter (L).
The volume units used in biology include liter (L), deciliter (dL), centiliter (cL), milliliter
(mL), microliter (µL), and nanoliter (nL). The liter has 10 dL, 100 cL, 1000 mL,
1,000,000 µL, and 1,000,000,000 nL. The volume of brake fluid in a 32-ounce container
is 946 mL. Express the volume of the brake fluid in µL.
A. 0.946
B. 94,600
C. 946,000
D. 9,460,000
E. 94,600,000
Answer: C
9.
The volume of a 12-ounce Coca-Cola can is 355 mL. Express this volume in Liters (L).
A. 355000
B. 35500
C. 0.355
D. 3.55
E.35.5
Answer: C
10.
To convert temperature in degrees Celsius to Kelvin, add 273 to the Celsius reading; to convert
temperature in Kelvin to degrees Celsius, take away 273 from the Kelvin reading. Body
0
temperature is kept constant at 37 C by homeostasis. Convert body temperature to Kelvin.
A. 310
B. 98.6
C. 236.6
D. 373.6
E. 337.6
Answer: A
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11.
The temperature unit in the metric system is the Kelvin (K). Water freezes at 273 K and
boils at 373 K. Zero Kelvin is the coldest theoretical temperature, called absolute zero
0
(equivalent to – 273 C). The Kelvin scale has no negative numbers. For everyday
0
purposes, however, we use degrees Celsius ( C), formerly called centigrade. The
0
temperature unit in the English system is degrees Fahrenheit ( F). A degree Celsius is the
same size as a Kelvin, but 1.8 the size of a Fahrenheit degree. While a Celsius
0
thermometer begins at 0, the Fahrenheit thermometer begins at 32. Water freezes at 0 C.
Convert this temperature to Kelvin.
A.
373
B.
273
C.
32
D.
16
E.
8
Answer: B
12.
Body temperature is kept constant by homeostasis at 98.6 F. What is body temperature in
0
degrees Celsius ( C)?
A.
373
B.
273
C.
212
D.
37
E.
32
Answer: D
13.
To convert temperature in degrees Celsius to degrees Fahrenheit, multiply the degrees Celsius
reading by 1.8 (or 9/5) and add 32 to the product. To convert a temperature reading in degrees
Fahrenheit to degrees Celsius, take away 32 from the Fahrenheit reading and divide the
0
0
remainder by 1.8. Water boils at 100 C and freezes at 0 C. At what temperature in degrees
0
Fahrenheit ( F) does water boil?
A. 310
B. 98.6
C. 212
D. 32
E. 32.6
Answer: C
0
9
14.
Light microscopes use visible light and glass lenses. The two basic types of light
microscopes are the compound light microscope and the dissecting light microscope.
These microscopes have limited resolution due to the nature of light. The electron
microscope uses a beam of electrons and magnetic lenses. Modern electron microscopes
can achieve a resolution of about 2 nm, while light microscopes cannot resolve detail
finer than 200 nm. There are two basic types of electron microscopes: the scanning
electron microscope (SEM) and the transmission electron microscope (TEM). Which of
the following statements about microscopes is correct?
A.
modern electron microscopes can achieve a resolution of about 2 nm, while light
microscopes cannot resolve detail finer than 200 nm
B.
instead of using light, the electron microscope focuses a beam of electrons
through the specimen or onto its surface
C.
there are two basic types of electron microscopes: the scanning electron
microscope (SEM) and the transmission electron microscope (TEM)
D.
the two basic types of light microscopes are the compound light microscope and
the dissecting light microscope
E.
all of these are correct
Answer: E
15.
Both the scanning electron microscope (SEM) and the dissecting light microscope give 3dimensional images of specimens, while the transmission electron microscope (TEM)
and the compound light microscope give only two-dimensional images. Both the
compound light microscope and the transmission electron microscope are used to
examine thin cross sections (c.s.) of specimens. Which of the following relationships
between a microscope and its use is mis-matched?
A. the changes in the shape of a living white blood cell – compound light microscope
B. the details of surface texture of a hair – scanning electron microscope
C. the detailed structure of an organelle – transmission electron microscope
D. the details of body structure of a living moth – dissecting light microscope
E. the movement of chloroplasts in elodea leaf cells – transmission electron microscope
Answer: E
16.
In a light microscope, visible light is passed through the specimen and then through glass lenses.
The lenses refract (bend) the light in such a way that the image of the specimen is magnified up
to 2,000 times as it is projected into the eye. Another important parameter in light microscopy is
resolving power or resolution, the ability of the microscope to distinguish between two adjacent
structures as two separate structures. Which of the following is an important parameter in light
microscopy?
A. magnification up to 2,000 times
B. resolving power or resolution
C. diameter of field of view
D. both A and B are correct
E. A, B, and C are correct
Answer: D
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17.
The fine structural details of cells and microorganisms did not become visible until the
1950s when electron microscopes became commercially available. Unlike light
microscopes, electron microscopes are not limited by resolution because they use beams
of electrons and magnetic lenses rather than light and glass lenses. The transmission
electron microscope (TEM) gives high magnification (up to 1,000,000X) and unlimited
resolution. The scanning electron microscope (SEM) gives much less magnification
compared to the TEM, but produces 3-D images. Electron microscopes cannot be used to
view processes in living cells. The advantage of light microscopy over electron
microscopy is that
A. light microscopy provides for higher resolving power than electron microscopy
B. light microscopy provides for higher magnification than electron microscopy
C. light microscopy allows one to view dynamic processes in living cells
D. Both A and B are correct
E. A, B, and C are correct
Answer: C
18.
Which of the following is a characteristic of electron microscopes as compared to light
microscopes?
A. have unlimited resolution and very high magnification compared to light microscopes
B. they are much more expensive than light microscopes
C. they utilize magnetic lenses rather than glass lenses
D. they utilize beams of electrons rather than light
E. all of these are correct
Answer: E
19.
Magnifications of more than 2,000X with light microscopes are considered "empty
magnification" because
does not improve with magnification beyond a certain
limit.
A. Resolution
B. Diameter of field
C. Depth of focus
D. Both A and B are correct
E. A, B, and C are correct
Answer: A
20.
Which of the following is mis-matched?
A. Light microscopes - glass lenses
B. Electron microscopes - magnetic lenses
C. Compound light microscope – parfocal
D. Transmission electron microscope - 3D images
E. dissecting light microscope – 3D images
Answer: D
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21.
The compound light microscope uses two sets of lenses to magnify objects. These are the
ocular lens and one of the four objective lenses. While the ocular lens magnifies 10 times
(10X), the objective lenses magnify 4, 10, 40, and 100 times (4X, 10X, 40X, 100X). The
objective lenses are the scanning (4X), low-power (10X), high-power (40X), and oilimmersion (100X) lenses. When using a compound light microscope, always begin
examining slides with the __________ objective lens.
A. 40X
B. Scanning
C. Low-power
D. High-power
E. Oil-immersion lens
Answer: B
22.
The compound light microscope employs two sets of glass lenses, the objective lenses and the
ocular lenses. The objective lenses are the scanning lens, which magnifies 4 times (4X); the lowpower objective lens, which magnified 10 times (10X); the high-power objective lens, which
magnifies 40 times (40X); and the oil-immersion lens, which magnifies 100 times (100X). The
ocular lens, which magnifies 10 times (10X), is attached to the eyepiece. The objective lenses are
held by a rotatable nosepiece. What is the function of the nosepiece in the compound light
microscope?
A. Holds the ocular lens
B. Holds the objective lenses
C. Brings images under focus
D. Focuses light on the specimen
E. Both A and B are functions of the nosepiece
Answer: B
23.
The iris diaphragm, also called the aperture diaphragm, is a variable diaphragm located within
the condenser. This device controls the diameter of the light beam coming up through the
condenser. When the diaphragm is nearly closed, light comes straight up through the center of
the condenser and contrast is high. When the diaphragm is wide open, the image is brighter and
contrast is low. The iris diaphragm is regulated according to the objective lens in use and the
type of slide viewed. The function of the iris diaphragm in the compound light microscope is to
A. Hold the objective lenses
B. Regulate the angle of light
C. Regulate the amount of light
D. Focus light from the light source onto the specimen
E. Regulate light resolution
Answer: C
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24.
The condenser of the compound light microscope is a lens beneath the stage that focuses
light from the light source onto the specimen through an opening in the stage. Adjustment
of the condenser is important for better resolution and contrast. The best position for the
condenser in your microscope is as close to the stage as possible. Adjustment of the
condenser is important for
A. better contrast
B. better resolution
C. higher magnification
D. A, B, and C are correct
E. only A and B are correct
Answer: E
25.
When a specimen is placed on the stage of a compound light microscope in an upright
position, it always appears inverted in the field of view. This means the image of the
specimen is both upside down and backward. Inversion of microscope images is caused
by the arrangement of the lenses in the microscope. Also, when you move the specimen
on the microscope stage up and down, to the left and to the right, the image moves in the
opposite direction. When you view a specimen with a compound light microscope, its
image appears
A. Upside down
B. Backward
C. Inverted
D. Upright
E. None of these
Answer: C
26.
When you look through the microscope, you see a circle of light. This is the field of view.
The diameter of the circle is called the diameter of field of view. Using a clear plastic
metric ruler you can easily measure the diameter of field of view with the scanning
objective lens (4X) and find it to be 4.3 mm. The diameters of field of view with the other
objective lenses are too small to be measured with a ruler. However, they can be
calculated. To find the diameter of field of view with the low-power (10X), high-power
(40X) and oil-immersion objective (100X) lenses, multiply the diameter of field of view
with the scanning lens by the total magnification obtainable by the scanning lens and
divide by the total magnification obtainable by the objective lens you want to determine
its field of view. The diameters of field of view with the 10X, 40X, and 100X objective
lenses are
A. 0.17mm, 0.43mm and 1.72mm, respectively
B. 4.30mm, 1.72mm and 0.43mm, respectively
C. 1.72mm, 0.43mm and 0.17mm, respectively
D. 10.75mm, 43.00mm and 107.5mm, respectively
E. 107.5mm, 43.00mm and 10.75mm, respectively
Answer: C
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27.
The diameter of field of view with the scanning objective lens (4X) is 4.3 mm. Calculate the
diameter of field with the high-power objective lens (40X) and express it in micrometers (µm).
A. 43
B. 430
C. 4300
D. 43000
E. 430000
Answer: B
28.
The diameter of field of view with the low-power (10X) objective lens is 1.7 mm. If
Paramecium takes up half the diameter of field of view, calculate the length of
Paramecium in micrometers (m).
A. 1,700
B. 850
C. 85
D. 8.5
E. 0.85
Answer: B
29.
As you increase the magnification of a compound light microscope, the diameter of field
of view decreases, the depth of field of view (or depth of focus) decreases, the working
distance decreases, and the light intensity decreases. Which of the following microscope
features decreases when the magnification increases?
A. Diameter of field of view
B. Depth of field of view
C. Working distance
D. Light intensity
E. All of these
Answer: E
30.
Resolution or resolving power of a microscope is defined as the minimum distance that
two points can be separated and still be distinguished as two separate points. Resolution
of light microscopes (L.R.) depends on the wavelength of light () and the numerical
aperture (NA) of the microscope lens. Resolution of light microscopes is limited due to
the nature of light. Magnifications of more than 2,000X with light microscopes are called
“empty” because light resolution does not improve with magnification beyond a certain
limit. Which of the following is the resolution of a light microscope if the wavelength of
light () is 400 nm and the numerical aperture of the microscope lens (NA) is 1.25?
[Hint: L.R. = 2NA].
A. 400 nm
B. 200 nm
C. 160 nm
D. 80 nm
E. 40 nm
Answer: C
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31.
Microscopes can be designed to magnify objects as much as desired, but the light
microscope cannot resolve detail finer than about 200 nm (0.2 μm), the size of a small
bacterium. This resolution is limited by the shortest wavelength of light used to
illuminate the specimen. Light resolution (LR) is calculated by dividing the wavelength
of light (λ) by twice the numerical aperture (NA) of the microscope lens in use, i.e., LR =
λ÷2NA. Which of the following is a correct definition of resolution?
A.
the minimum distance two points can be separated and still be distinguished as
two separate points
B.
the ratio of an object’s image to its real size
C.
the distance between the lens and the specimen
D.
both A and B are correct
E.
A, B, and C are correct
Answer: A
32.
The dissecting (stereoscopic) light microscope is used to view larger specimens at low
magnification. It usually has a binocular eyepiece tube, a long working distance, a wide
field of view, and a low range of magnifications, typically 5X to 50X. A dissecting
microscope always has two eyepieces and two objective lenses, one for each eye. It uses
two separate light paths to get a true stereo image of the object viewed. Because of this,
the dissecting microscope gives 3-D images of the specimen. This makes it suitable for
viewing whole objects or looking at complex 3-D specimens. What advantage does the
dissecting microscope has over the compound microscope?
A. higher magnification
B. better resolution
D. 3-D images
C. lower price
E. all of these
Answer: D
33.
The human eye has a limited resolution of about 100 micrometers (μm). This is the
minimum distance two objects can be apart and still be distinguished by the human eye as
two separated objects. Because cells are few micrometers in diameter, they cannot be
seen with the unaided eye. One way to improve resolution is to increase magnification
using microscopes so that small objects appear larger. The compound light microscope
uses ocular lenses and objective lenses to achieve very high magnification and clarity.
The ocular lenses focus the image of the object on the objective lenses, which magnify it
again and focus it on the retina on the back of the eye. Light microscopes that magnify in
stages using several sets of lenses are called compound microscopes. They can resolve
cell structures that are separated by more than
A.
200 nanometers (nm)
B.
100 nanometers (nm)
C.
50 nanometers (nm)
D.
10 nanometer (nm)
E.
5 nanometers (nm)
Answer: A
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34.
The use of stains that bind to specific molecular targets in cells has been a powerful tool
for viewing cell structures and analyzing their functions. Which of the following staining
procedures used in the biology lab is incorrect?
A.
human cheek cells – methylene blue
B.
onion skin cells – iodine
C.
potato tuber cells – iodine
D.
elodea leaf cells – safranin
E.
all of these are correct
Answer: D
35.
Which of the following instruments and/or procedures are employed to view cells and
cell structures?
A.
staining procedures
B.
compound light microscopes
C.
scanning electron microscopes
D.
transmission electron microscopes
E.
all of these are correct statements
Answer: E
36.
Biologists collect data from observations or experiments and use statistical analysis to
interpret data and to draw conclusions. Simple statistics that biologists calculate include
mean, median, range, variance, and standard deviation. The mean is the arithmetic
average, and the median is the middle value of a group of measurements. If the heights of
five of your classmates are 180, 176, 174, 170, and 168 cm, calculate mean height.
A.
173.6
B.
176.6
C.
178.6
D.
180.6
E.
182.6
Answer: A
37.
What is the median of the measurements in the previous question?
A.
168
B.
170
C.
174
D.
176
E.
180
Answer: C
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38.
If the range of data is the difference between the smallest and largest measurement, what
is the range of the measurements in question 36?
A.
4
B.
6
C.
10
D.
12
E.
24
Answer: D
39.
The variance and standard deviation provide information about how the measurements
vary about the mean. They help investigators understand the spread of the values in a
sample. To measure the variance, calculate the deviation of each measurement from the
mean, square each deviation, sum the squared deviations, and divide by the number of
measurements minus one (N-1). What is the variance of the measurements in question
36?
A.
18.2
B.
22.8
C.
44.4
D.
91.2
E.
123.8
Answer: B
40.
What is the standard deviation of the measurements in question 36?
A.
4.8
B.
6.7
C.
9.5
D.
11.1
E.
12.1
Answer: A
17
Fill-in-the-blank Questions: Use following word bank:
Resolution
Metric system
Field of view
Objective lens
Adjustment knob
inverted
micrometer
electron microscope
ocular lens
base unit
iris diaphragm
milligrams
dissecting microscope
microscope condenser
deciliter
total magnification
parfocal
depth of focus
working distance
nosepiece
41.
The objective lenses are held by a rotatable _______________.
Answer: nosepiece
42.
A _______________ has 100 milliliters.
Answer: decimeter
43.
The __________ __________ of mass is the gram.
Answer: base unit
44.
The microscope part that brings objects into focus is the __________ __________.
Answer: adjustment knob
45.
The compound microscope has four __________ __________ held by the nosepiece.
Answer: objective lenses
46.
The __________ __________ renders the real image produced by the objective lens
visible as a virtual image.
Answer: ocular lens
47.
The __________ __________ is a lens beneath the stage that focuses light from the light
source onto the specimen through an opening in the stage.
Answer: microscope condenser
48.
The distance between the objective lens and the specimen on the stage is called the
__________ __________.
Answer: working distance
49.
The thickness of an object that is in sharp focus is referred to as the __________
__________ __________.
Answer: depth of focus
50.
The light microscope that produces 3-D images of whole objects is the __________
___________.
Answer: dissecting microscope
51.
The __________ __________ uses a beam of electrons and magnetic lenses.
Answer: electron microscope
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52.
The circle of light you see when you look through the light microscope is called the
__________ __________.
Answer: field of view
53.
The __________ __________ of measurements is used all over the world except in the
U.S.
Answer: metric system
54.
A _______________ is 1000 nanometers long.
Answer: micrometer
55.
A gram weighs 1000 _______________.
Answer: milligram
56.
The objective lenses of a compound light microscope are _______________; that is, once
an object is in focus with the low power objective lens, it’s also in focus with the high
power objective lens.
Answer: parfocal
57.
__________ __________ of a compound light microscope is the product of the
magnification with the ocular lens and the magnification with the objective lens.
Answer: total magnification
58.
The part of the compound light microscope that controls the amount of light coming up
through the condenser is called the __________ __________.
Answer: iris diaphragm
59.
Images produced by the compound light microscope are called _______________
because they are both backward and upside down.
Answer: inverted
60.
The ability of a microscope to distinguish two closely spaced structures and discern small
distances between them is called _______________.
Answer: resolution
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True/False Questions
61.
If you want to study the internal ultrastructure of cells, you most likely would use a
compound light microscope.
Answer: False
62.
The minimum distance two points can be separated and still be distinguished as two
separate points using a microscope is called resolving power or resolution.
Answer: True
63.
Modern electron microscopes can achieve a resolution of about 2 nm, while light
microscopes cannot resolve detail finer than 200 nm.
Answer: True
64.
Instead of using visible light, the electron microscope focuses a beam of ultra-violet light
through the specimen or onto its surface.
Answer: False
65.
You need a transmission electron microscope (TEM) to study the movement of
chloroplasts in elodea leaf cells.
Answer: False
66.
You need a compound light microscope to study the changes in the shape of a living
white blood cell.
Answer: True
67.
When a specimen is placed on the microscope stage in an upright position, it always
appears inverted in the field of view.
Answer: True
68.
The transmission electron microscope (TEM) gives high magnification and 3-D images.
Answer: False
69.
Light microscopes use light as a source of illumination and magnetic lenses for
magnification.
Answer: False
70.
The thickness of an object that is all in sharp focus with one microscope setting is called
field of view.
Answer: False
71.
Objective lenses are usually classified in terms magnifying power, numerical aperture,
and degree of optical correction.
Answer: True
20
72.
The transmission electron microscope (TEM), so called because electrons used to
visualize specimens are transmitted through the material, is capable of resolving objects
only 0.2 nanometers apart.
Answer: True
73.
The scanning electron microscope (SEM) scans a beam of electrons across the surface of
a specimen, and the reflected electrons are amplified and transmitted to a screen where
the image can be viewed and photographed. The SEM gives 3-D images and has
improved our understanding of many biological phenomena.
Answer: True
21
Short-Essay Questions
74.
List some of the advantages of the metric system of measurements over the English
system.
Uses decimals rather than cumbersome fractions; uses base units and prefixes that
eliminate the use of long rows of zeros; it’s an international system used all over the
world
75.
Why is it important for all scientists to use a standard system of measurements
rather than the system that may be most popular in their home country?
Unity and easy communication and understanding among scientists
76.
Why is it important for college students to be familiar with the metric system?
The government and all the manufacturers and industries are going metrication. Knowing
the metric system will be a prerequisite to get a job.
77.
Which type of microscope would you use to study (a) the changes in shape of a living
white blood cell, (b) the details of surface texture of a hair, and (c) the detailed
structure of a cell organelle?
(a) Light microscope, (b) scanning electron microscope (SEM), (c) transmission electron
microscope (TEM)
78.
Compare the compound light microscope to the dissecting light microscope and
indicate the advantages and disadvantages of each.
Both microscopes use light and are limited by light resolution. The compound
microscope uses two sets of lenses in a series, and thus gives greater magnification
compared to the dissecting microscope which uses a single set of lenses. The dissecting
microscope gives 3-D images while the compound microscope gives only 2-D images.
79.
Compare the light microscope to the electron microscope and indicate the
advantages and disadvantages of each.
Light microscopes use light for illumination and glass lenses for magnification. Electron
microscopes use electrons for illumination and magnetic lenses for magnification. The
electron microscope is not limited by resolution and gives much higher magnification
compared to the light microscope.
22
80.
Define microscope resolution. Indicate how to improve resolution in light
microscopes.
Resolution of a light microscope is the ability of a microscope to distinguish two closely
spaced structures and discern small distances between them. Resolution of a light
microscope is calculated by dividing half (0.5) the wavelength of light by the numerical
aperture (N.A.) of the objective length. Light microscopes have limited resolution due to
the nature of light. Resolution of light microscopes can be improved by using light with
shorter wavelength (λ) and/or by using objective lenses with higher numerical apertures.
23