Work in the living
environment/biology laboratory requires some knowledge about
and the ability to use several pieces of specific scientific
apparatus. Some of these tools include the
compound microscope for looking at microscopic specimens
and the dissection microscope for looking at three
dimensional specimens larger than the naked eye. More
specialized laboratory techniques include that of gel
electrophoresis and paper chromatography.
Measurements of mass, volume, and length
are commonly required in lab.
The triple beam balance
and graduated cylinder are other commonly used pieces of
equipment for determining mass and volume
respectively. Various types of rulers may be employed to
provide measurements of length depending upon the specimen
being studied or observation being made.
the Light Microscope
- eyepiece or ocular
- body tube
- fine adjustment
- high power
- low power
- mirror (many
microscopes have a light instead)
- coarse adjustment
- stage clip
- inclination joint
Functions of the Light Microscope Parts
eyepiece (ocular) - where you look through to see the
image of your specimen.
body tube-the long tube that holds the eyepiece and
connects it to the objectives (not labeled)
fine adjustment knob-small, round knob on the side of
the microscope used to fine tune the focus of your specimen
after using the coarse adjustment knob
nosepiece-the rotating part of the microscope at the
bottom of the body tube; it holds the objectives
high power objective -- used for high power
magnification of the specimen (the longer objective lens)
low power objective -- used for low power magnification
of the specimen
diaphragm-controls the amount of light going through to
light or mirror-source of light usually found near the
base of the microscope; makes the specimen easier to see
base-supports the microscope
coarse adjustment knob -- used for focusing on low
arm-part of the microscope that is grasped when one
carries the microscope
clips-shiny, clips on top of the stage which hold the
slide in place
(The specimen is placed on the stage for viewing.)
inclination joint -is used to tilt the microscope
Microscope Usage Rules
- Always carry the microscope
with two hands - one on the arm and one underneath the
base of the microscope. Hold it up so that it does not hit
- Do not touch the lenses. If
they are dirty, ask the teacher for special lens paper or
ask your teacher to clean the lenses for you.
- Never use the course adjustment
knob on high power. The lens is closer to the stage making
it easier to break a slide or the lens itself.
Notify teacher if a slide or
cover slip breaks. Students should not handle broken glass.
- If using a microscope with a light,
turn off light when not in use
6. Always clean slides and
microscope when finished. Store microscope set on the
lowest power objective with the nosepiece turned down to its
lowest position (using the coarse adjustment knob). Cover
microscope with dust cover and return it to storage as
directed by your teacher.
Points About the Compound Microscope
1. Always begin focusing on the
lowest possible power. Remember to center the specimen you are
observing in the field of view before switching to a higher
power. Make certain that you move the objectives away from the
specimen when focusing so their is no collision between the
objective being used and the slide/cover slip which may damage
the objective lens.
2. As you switch from low to high power, the field of view
becomes darker. To deal with this the diaphragm needs to be
opened to allow in more light. (Frequently on low power the
diaphragm needs to be partially closed as it is too bright.)
3. As you switch from low to high power the field of view
Images viewed under the
light microscope are reversed (backward) and
inverted (upside down). This is a compound light
microscope view of the letter F placed on a slide in its
Paper chromatography is a procedure used to separate
substances in a mixture. In the Living Environment/Biology
lab, this mixture is usually a solution of liquid plant
pigments containing different kinds of chlorophylls and other
colored photosynthetic pigments.
A small concentrated sample of a mixture is placed on the
chromatography paper above the line of a solvent mixture. The paper is contact with a solvent solution at its bottom.
This solvent moves through the paper due to capillary action
and dissolves the mixture spot. Some parts of the solvent
mixture to be separated have a greater attraction for the
chromatography paper, so they move a lesser distance, while
other parts of the solvent mixture have a lesser attraction,
so they move a greater distance up the paper.
Paper Chromatography of a Plant Pigment
The specific mixture placed on
chromatography paper will separate into consistent patterns as
long as the same solvent, paper, and amount of time allowed
for the separation are not changed. Different solvents will
change the separation pattern of the mixture. Mixtures that
are colored can be separated into component colors by paper
The Rf value of a pigment is a
statistic often computed from a chromatography separation. Each pigment in the solution
will have a specific Rf for the same solvent when the
chromatography occurs for a specific length of time.
Calculation of Rf
distance the pigment travels from the original
spot of solvent
distance to the wetting front of the solvent
Gel electrophoresis is a procedure used to separate charged
molecules of different sizes by passing them through a gel in
an electrical field. The gel serves to act as a support for
the separation of the molecules of different sizes. The gel
is usually composed of a jelly-like material called agarose
which is made from seaweed.
such as DNA fragments of different lengths and proteins
of different sizes are often separated in the gel. Holes are created in the gel which serve to hold the
particular DNA mixtures to be separated. The DNA
fragments are then loaded into the wells in the gel.
contains very small holes which act to regulate
the speed which molecules can move through it
based on the size of the molecules. The smaller
molecules will move much more easily through the
small holes in the gel. As a result, large
fragments of DNA lag behind small fragments, thus
allowing the experimenter to separate these
molecules based on their size.
molecular weight markers are electrophoresed along with the
specimen, so the experimenter may know the size of the DNA
fragment which has been separated. Different individuals or
organisms form different banding patterns in the plate when
their DNA has been separated. DNA is cut into pieces for
separation for electrophoresis by restriction enzymes.
These enzymes were originally discovered in bacteria and were
used by the bacteria to defend themselves from invasion by
other bacteria and viruses.
for the Gel Electrophoresis DNA Separation
- It may be used to
determine an individual's genetic relationship to his
or her ancestors, as the more closely matched the
banding pattern between two individuals, the more
closely they will be genetically related. In theory,
no two individuals will form the same DNA banding
pattern when the electrophoresis is completed.
- It may be used to
identify an individual that have committed crimes
based on the ability to match the suspects DNA to
evidence which has been collected at a crime scene.
- It may be used to
determine evolutionary relationships between
organisms, as organisms with a closer genetic
relationship will form more similar banding patterns.
Electrophoresis Setup with Power Supply
Measurements of mass, volume, and length are commonly
required in lab. The
triple beam balance and graduated cylinder are other
commonly used pieces of equipment for determining mass and
volume respectively. Various types of rulers may be
employed to provide measurements of length depending upon
the specimen being studied or observation being made.
A commonly used instrument to measure liquid volume is the
graduated cylinder. This
instrument usually measures liquid volume in milliliters
a Graduated Cylinder
is important to remember to read to the bottom of
the curved line or meniscus when measuring
solutions involving water or most liquids. The
graduated cylinder at the left is divided into increments of 2 ml, so the volume in it is 12 ml. The graduated cylinder on the right is divided into
increments of 1 ml, so the volume in it is 16 ml.
The triple beam
balance is commonly used to measure mass in the
biology lab. This device is named for its three long beams
on which sliding bars called riders (or tares) are used to
determine the mass of an object placed on its platform. It
is very important that the riders on the rear beams are in
the notch for the whole number of grams and not in between
notches. The front beam is a sliding scale graduated in
grams. The rider on this beam can be positioned anywhere
on the scale. Masses on a triple-beam balance can be read
to tenths of a gram and estimated to hundredths of a gram.
the Triple Beam Balance
The picture at the upper
left shows two different models of triple beam
balances commonly used in the biology laboratory.
The picture at the lower left shows the measurement
of a mass in progress. Without estimation, the
mass of the object appears to be 373.3 grams (g).
Most measurements in biology will involve metric units of
measurement. When using a ruler, it is good to start at a whole number
increment that isn't 0. Many times the end of a ruler will
be worn away by student/teacher use or is inaccurate due
to the manufacturing process. It is important to remember
to take away the whole number increment one has moved in
on the ruler (in the example below 1 cm) from the
a Ruler to Measure Length
How long is leaf A?
The tip of
the leaf is at about 6.5 cm, but note the
measurement started at 1 cm. Therefore, Leaf A is
5.5 cm or 55 mm. in length.
The magnifying power
of most objectives and oculars is engraved on them. On the
ocular, the marking can be found on the top edge or on the
smooth cylinder that fits inside the body tube; on the
objectives, magnification is on the side of the cylinder.
For example, a marking "10x" means that the particular
lens forms an image ten times larger than the object being
viewed. The total magnification of a microscope is equal
to the power of the eyepiece (ocular) X power of the
objective used. For example, if a student is using a
microscope with a 10 X ocular and a 43 X high power
objective, the total magnification of the specimen the
student is viewing is equal to 10 X 43 or 430 X (times).
Formula for Total Microscope Magnification
Power of the eyepiece
Measuring the diameter of the
field of view on a microscope can be made by
placing a clear metric ruler on the stage of a microscope.
The light microscope is used to look at cells or other
similarly sized microscopic objects, so small units of
measure such as millimeters or micrometers are used.
It is important to remember that there are 1,000
micrometers in 1 mm (millimeter) and 1000 millimeters in a
Finding the Size of a Microscope Field of View
In the pictured field of
view at the left, it can be observed that there are
approximately 3 1/2 divisions equal to a length of
3.5 mm. Therefore this field of view is
equal to 3.5 mm
or 3,500 micrometers.
Finding the Size of Multiple Cells in a Field of
The two cells in this
field take up a field of view of one millimeter.
Therefore, the size of the specimen is equal to 1
mm/2 cells or 0.5 mm per cell. There is 500
micrometers in 0.5 mm., so the average size of each
cell is 500 micrometers.
Estimating Cell Size When the Field of View is Known
It is often difficult to
approximate the approximate size of the field of
view, but this ameba considered lengthwise appears
to occupy approximately 1/3 of the field of view.
The field of view in the left image is 3 mm. Given
that the ameba in the image takes up about 1/3 of
that field, we can find its approximate length by
multiplying the 3 mm X 1/3 = 1 mm length or
1,000 micrometers for the approximate length of this
The student is viewing the same ameba in the field
of view at the right on a higher power. The field of
view gets smaller which makes the ameba appear
larger in this field.