Microscope Usage Lab and Focusing Test
Purpose:
The purpose of this lab to examine slides representing key stages in the evolution of life
on Earth. In addition, this lab will prepare the student for subsequent laboratory
courses (Bio II, API, Micro) where microscope skills are required.
Introduction:
The earliest evidence of life on Earth is prokaryotic. Both archaean and bacterial cells
are prokaryotic. The size of prokaryotes, such as bacteria and archaeans, is generally
much smaller than that of the typical eukaryotic cell seen in plants, animals, fungi or
protists.
Cyanobacteria such as Oscillatoria were a likely source of the first large volumes of
oxygen, as a result of oxygenic photosynthesis. Thus, they paved the way for the rest
of us oxygen consumers who use oxidative phosphorylation to live. Oxygen in the
atmosphere also enabled the development of an ozone layer which protected the
surface of the Earth from ultraviolet light, allowing the terrestrial environment to be
colonized by living things.
The development of the eukaryotic cell was one of the most significant evolutionary
transitions to occur, particularly from our perspective. This cell type has many
membrane bound compartments within it, including the nucleus, endoplasmic reticulum,
in addition to elements not found in prokaryotes such as mitochondria, and
chloroplasts. The larger size and division of labor, which the compartmentalization of
the eukaryotic cell allows, provides an ability to produce the large volumes of proteins
and other products which multicellular life requires, and allowed the diversification of
cell types within organisms via emphasis of particular compartments within these cells.
Thus, the eukaryotic cell is the type of cell found in animals, plants, fungi, and protists.
Protists resemble the types of eukaryotes from which plants, animals and fungi evolved.
Most protists have a unicellular lifestyle like that of prokaryotes.
Lab Activities:


Microscope Focusing Lab (review evolution of life)
Microscope Focusing Test
Materials Needed:
 4 demonstration microscopes set at: 4X, 10X, 40X and oil immersion (100X).
 Student slides of: Oscillatoria, Amoeba, Paramecium, Ceratium, Volvox, Planaria,
simple columnar epithelium
 Separate microscope testing area with Volvox slide.
Procedure:
1. Students are to view the bacterial demonstration slides (prokaryotes) at the three
different magnifications. (10X, 40X, and oil). Students should recognize the difference
in each magnification. The slides show examples of the various shapes of bacteria
including: coccus (round shape), bacillus (rod-shaped), and spirochete (spiral shaped).
The oil immersion slide shows bacteria in blood. Note the size difference between the
eukaryotic cell (red blood cell) and the prokaryotic cell (bacteria).
2. Students are required to review simple eukaryotes (Amoeba and Paramecium),
flagellated eukaryotes (Ceratium) which demonstrates the 3 modes of locomotion
(flagellar, ciliary, and amoeboid), colonial eukaryote (Volvox), multicellular eukaryote
(Planaria) and a tissue (simple columnar epithelium).

In the Amoeba slide, note the outstretching pseudopodia, which it uses to move
and capture food. These are extensions of its cytoskeleton which it grows and
retracts (using ATP) to extend its membrane and body.

In the Paramecium slide, note the many cilia (made of microtubules) which it
uses to move and spin. Also note the large contractile vacuole which regulates
water content. Try also to identify the nucleus. This organism has two nuclei: a
large macronucleus and a small micronucleus.

Ceratium is a dinoflagellate. Two flagella are used for movement. Many

Volvox is a colonial form of green algae, which is similar to the ancestor of land

Notice that different parts of Planaria’s multicellular body, which are adapted for
different activities. The head carries eyespots which can sense light. Long, dark
repositories of sperm and eggs line either side of the body from head to tail, thus
providing a specific area for these reproductive cells to grow. Towards the center
is the pharynx (mouth) and gastrovascular system, which takes in nutrients.
Because it is so small and flat, nutrients and gases can then diffuse throughout
dinoflagellates also have a sort of armor surrounding them called a theca.
Dinoflagellates are an important part of the marine ecosystem, and because they
contain chloroplasts and are part of the phytoplankton. This protist occasionally
gathers in large numbers in the marine environment and produces toxins in great
quantities which are responsible for large-scale fish die-offs known as “red tide”.
plants. Notice how the cells are associated to form spheres within spheres. Some
of these inner spheres produce male gametes while other spheres produce
female gametes. This colonial form and specialization of parts is expected to
have eventually led to the complex multicellular tissues seen in land plants.
Similar colonial forms very likely were the predecessors of animals and fungi, as
well.
its body without the need of a cardiovascular system. While Planaria is simple for
an animal, its specialization of sections of its body makes it highly adaptive.

A tissue is a cellular organizational level intermediate between cells and a
complete organ. Epithelial tissue covers the organ surfaces such as the surface
of the skin, the airways, the reproductive tract, and the inner lining of the
digestive tract. Simple columnar cells are a single layer of tall cells that are
arranged like pillars. They are found in the inner lining of the intestine, secrete
digestive enzymes and perform the function of absorption of digested food.
3. Students are to practice their focusing techniques using these organisms and the
tissue above at 4X, 10X, and 40X magnifications. Make sure to use both eyepieces.
Practice changing from one power to the other by moving the new objective into place
and adjusting with the fine focus (do NOT focus by looking sideways at the slide and do
not adjust with the coarse adjustment after switching from 4X).
4. When the student feels they are ready, they are to proceed to the microscope
focusing test area. Students will be handed a slide and will be given 2 minutes to show
their ability to focus the slide at 4X, 10X, and 40X.
Grading for microscope test:
Maximum points available for the test is 20 points (to be added to the final practical).
Students who fail the first attempt will have 10 points deducted. Students who fail both
attempts will lose the entire 20 points.
Students with a legitimate, documented excuse for not attending this lab will be
required to take the microscope focusing test after they have completed their final lab
practical. Please note only the focusing test will be conducted, students will not be
allowed to practice for the make-up.
Checklist for microscope test (failure to demonstrate any of the items listed below will
result in a failed microscope test:
 Slide is placed on stage between stage clips (not under the clips)
 Slide is focused at 4X
 Uses nosepiece to change objective
 Does NOT use coarse adjustment knob once you have switched to a higher
objective from the 4x.
 Slide is focused at 10X
 Slide is focused at 40X
Draw your organisms/tissue here:
Bacteria (10X)
Oscillatoria (
X)
Ceratium ( X)
Simple Columnar Epithelium
Bacteria (40X)
Bacteria (100X)
Amoeba ( X)
Paramecium ( X)
Volvox ( X)
Planaria ( X)