LAB #7: Microscopes and the Cell – Basic Unit of Life
TARGETS
II. Visually identify & explain the function of the following cell organelles: ribosome, endoplasmic
reticulum (rough & smooth), Golgi complex, mitochondrion, vacuole, & chloroplast
III. Describe how organelles interact to accomplish a task within a cell, tissue, organ, or organism
IV. Compare & contrast prokaryotic & eukaryotic cells
D. Use a light microscope to view specimens and describe the relationship between size of field of view,
objective lens magnification, and total magnification
Introduction
Types of Cells
Living organisms exhibit certain fundamental properties that we have come to recognize as being
characteristics of life, such as digestion, respiration, excretion, reproduction, and so on. The smallest
entity that can carry out these characteristics is the cell. All living organisms are composed of cells and
cell products. The German botanist Matthias Schleiden and the German zoologist Theodor Schwann first
proposed this generalization, known as the Cell Theory, in 1839.
Cells are both the structural and functional units of all living organisms. Cells are the basic
building blocks, so to speak, of all organisms; the bricks, as it were, out of which the house is built. All the
organisms on this planet are divided into two groups, depending upon their cell type: the prokaryotes and
the eukaryotes. The cells of prokaryotes do not contain a well-defined nucleus, or any membranous
organelles in their cytoplasm. The cells of eukaryotes, on the other hand, do possess a well-defined,
membranous nucleus, and a large number of cytoplasmic, membranous organelles. Eukaryotic cells are
generally larger and more complex than prokaryotic cells. Only organisms in domains Bacteria and
Archaea are composed of prokaryotic cells. All other organisms including plants, animals, protists, and
fungi are eukaryotic. In lab we will focus our attention on the details of eukaryotic cells.
Most cells are very small and can be seen only with the aid of a microscope. Some cells, however,
such as the eggs of birds, are large enough to be seen with the naked eye. Different kinds of cells may
have different shapes. Some may be flat and tile shaped, others may be spherical or globular, and others
may be cylindrical, or long and fiber-like. Most cells have a diameter between 0.5mm and 40mm; others,
such as human nerve cells, may be as long as 90cm. Clearly, cells occur in many different sizes and
shapes, depending upon their location and function. There is probably no such thing as a "typical" or
"generalized" cell (except in textbooks and lab manuals). Yet, despite the differences in size and shape,
when any cell is examined under a light microscope, a number of small structures, called organelles, can
be seen that are common to almost all cells.
Prokaryotic Cells - Bacteria and cyanobacteria are prokaryotes, and thus do not contain a
membrane-bound nucleus nor any other membrane-bound organelles. Prokaryotes are simple cells
because evidence suggests these were the first life forms on Earth. Prokaryotes have no well-defined
organelles, but their cellular contents are enclosed in a plasma membrane and surrounded by a
supporting cell wall. Prokaryotes are able to manufacture proteins with the help of ribosomes. Ribosomes
are not membrane-bound organelles.
Eukaryotic Cells - Eukaryotic cells contain nuclei and membrane-bound organelles. Nuclei
contain the genetic material (chromosomes) of a cell. Organelles provide unique compartments within the
eukaryotic cell for metabolic tasks to take place. Each organelle has a unique internal environment that
optimizes the functionality of enzymes and other molecules that exist within. It is important to note that
organelles do not exist nor operate in isolation. Most cellular tasks require the contributions from many
different organelles. The functionality of a group of similar cells (tissues) relates to the kind and
abundance of organelles present. For example, muscle cells require large amounts of ATP energy to
contract and therefore cause bones to move a human. Muscle tissue contains cells that are packed with
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mitochondria to supply the energy necessary for proper function. Eukaryotic cells evolved after
prokaryotes. The unique organelles of eukaryotic cells created the great biodiversity that we see in
organisms from Kingdoms Plantae, Animalia, Fungi, and all the protist super groups.
Microscope Use
The microscopes used in AP biology lab are expensive, precise optical instruments that allow
students to view a variety of objects and organisms. Before using the microscope, the student must have
detailed knowledge of the parts and functions of the microscope. Complete page 7-8 this lab handout
before performing the microscope lab in class.
There are four objective lenses on the rotating nosepiece of the microscope. The scanning power
lens (red stripe) magnifies objects at 4x. The scanning power lens should be used first to locate and focus
your specimen using both the coarse and fine adjustment knobs. The low power lens magnifies objects at
10x (yellow stripe). The high power lens magnifies objects at 40x (blue stripe). The oil immersion lens is
rarely used in class, but it magnifies objects at 100x (white stripe) when used with immersion oil. The
eyepiece lens magnifies objects at 10x. The total magnification of objects viewed is the product of the
eyepiece lens and objective lens magnifications. For example, an object viewed with the scanning power
lens is viewed at a total magnification of 40x = 10x (eyepiece) • 4x (objective). Additional contrast and
clarity of the specimen can be obtained by adjusting the amount of light used to view the specimen. Use
the iris diaphragm knob below the stage to control both the amount and angle of light going to the
specimen.
Please use care when transporting and using the microscope. The microscope should always be
carried using both hands and is held close to the body. The cord should be wrapped around the base of the
microscope during transport. Place the microscope on a level surface when in use. When finished using
the microscope, remove slide from stage, turn off the power, unplug and wrap the power cord around the
base of the microscope, place dust cover over the microscope, and return the scope to the storage shelves
by carrying it with two hands close to your body.
Cell structures
1. Cell membrane (plasma membrane) - surrounds the cell and regulates the flow of materials into and out
of the cell.
2. Nucleus - usually spherical or ovoid; contains the genetic information for controlling all the activities of the
cell; normally only one per cell, usually located near the center of the cell.
3. Cytoplasm - the fluid material located between the nuclear envelope and the cell membrane.
4. Vacuoles - membranous bags or sacs that are usually filled with liquid; may contain food or may collect
liquid that is to be eliminated; often serve as storage organelles.
5. Chloroplast - found only in cells of green plants and photosynthetic protists contain chlorophyll and are the
sites of photosynthesis.
6. Cell Wall - found in plants, fungi, prokaryotes and photosynthetic protists, but not in animal cells; it
surrounds the cell membrane and provides rigidity, support and protection; the principal
component of the eukaryotic cell wall is cellulose.
The study of cells is called cell biology and is generally divided into two sub-disciplines: cytology
and cell physiology. Cytology is the study of cellular structures, while cell physiology is concerned with
the functions of those structures. Many studies of cell structures are presently conducted by using an
electron microscope. The electron microscope enables the cell biologist to take pictures (electron
micrographs) of cellular organelles that are too small to be resolved by the ordinary light microscope.
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These structures are submicroscopic and sometimes referred to as the ultra structures of the cell. The
electron microscope has enabled biologists to unravel the hidden, submicroscopic structure of the
organelles listed above. In addition, a number of new organelles have been discovered in the cytoplasm
that were never visible with the light microscope. Such organelles include:
1. Endoplasmic reticulum (rough and smooth) - internal transport of materials and synthesis of
macromolecules
2. Mitochondria - production of energy (ATP)
3. Golgi apparatus (Golgi body) - plays a role in secretion of cellular protein products
4. Ribosomes - site of protein synthesis
You will not be able to observe these last four structures in class. If the proper biological stain is used, the
mitochondria and Golgi body can be seen under the light microscope. Such a technique, however, has not
been used on the microscope slides that you will be using in this course. You will be limited to observing
only the six structures previously listed on page 3.
Procedure
Part A: Optical properties of the light microscope & lenses
Obtain a small section of newspaper. Cut out a lower case “e” from the print and place the letter on
the glass slide so you can read it. Add one drop of water and place a cover slip over the “e”. Place the
slide with “e” onto the microscope stage so the letter is facing you. (Your teacher may have already cut
out the “e” and mounted it to a slide. Therefore, obtain an “e” slide and follow the directions below.
Focus the “e” using the scanning power objective lens (4X). What do you notice about the
orientation of the letter as it is viewed through the objective and ocular lenses? Draw what you see in
the space provided on page 9 of lab.
Focus the “e” using the low power & high power objective lenses. How does the size of the letter
change as you increase magnification? How does the size of the field of view change as you increase
magnification? Write down observations and draw the letter at high power magnification on page 9 of
handout.
Remove the “e” slide from the stage. Place a transparent, metric ruler across the field of view
(FOV) and quantify the size of the FOV at a total magnification of 40X, 100X, and 400X. Write your
measurements on page 9 of the lab handout. As you increase magnification, name a qualitative
observation about the FOV.
Part B: Human Hair
Prepare a wet mount of 2 different colored human hairs: 1 light & 1 dark from
you, your lab partner, or a classmate! Cross 1 hair over the other in the center of the
slide. Add a drop of water or two, and then place a coverslip over the hairs & water. Cut
off excess hair that is hanging off the slide
Place the crossed hairs centered in the center of the field of view. Using the scanning power
objective (4X), coarse adjustment knob, and fine focus knob to focus the hairs at scanning power. Change
to the low power objective (10X) by rotating the nosepiece, and adjust the diaphragm for the best light.
You should be able to determine which hair is crossed over the other.
Sketch, IN DETAIL, the size, texture, and color of the hairs in the space provided on page 10.
Don’t draw something similar to the set-up picture. Calculate & label the total magnification.
Part C: Cabomba and Onion
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To observe a living plant cell, obtain a small piece of leaf from the Cabomba plant on the front
table. Cabomba is an aquatic plant that is commonly used in home aquariums and can be purchased in pet
shops and aquarium supply stores. Prepare a wet mount of a small piece of Cabomba leaf, using warm
water. Under low power examine the leaf along the outer edge; here the leaf is normally only two-cells
thick. The center of the leaf may be too thick to allow light to pass through it, thus prohibiting any
observations.
Locate the green chloroplasts in the cytoplasm of the cells. Note the shape of each cell. (What
shape is it? Can you see the cell walls separating each cell?) If the leaf has been in warm water for ten
minutes or more, the cytoplasm may be moving around inside the cell, in somewhat of a circular direction.
This movement of the cytoplasm is called cytoplasmic streaming, or cyclosis. If cyclosis is occurring, the
chloroplasts will be passively carried along by the cytoplasm. Tell me if cyclosis is taking place so that I
can call other students to view this. Sketch several cells on page 10 of lab handout at high power and
label them as well as indicating the total magnification of your specimen.
Structures of onion cells are enhanced for observation by using stains. A stained specimen is
prepared by adding a dye that preferentially colors some cell parts but not others. Iodine a common stain
and accumulates in cell walls and nuclei. Nuclei appear as dark, dense bodies in the translucent cytoplasm
of the cells.
Examine stained onion cells and sketch what you see at high power on page 10 of handout.
1. Cut an onion into fourths, and remove one of the fleshy leaves.
2. Snap the leaf backward and remove the thin piece of epidermis formed at the break point
3. Place this epidermal tissue on a microscope slide, add 2-3 drops of iodine stain, and place a cover
slip over the stain and onion epidermis.
4. Allow iodine stain to stay on the tissue for ~20 seconds.
5. Place slide on an angle so one side is elevated. Fold a piece of paper towel many times and place
the folded paper towel at the low end of the slide next to the cover slip.
6. Add several drops of distilled water at the edge of the cover slip on the higher side. The water will
wash across your onion specimen and remove the excess iodine stain from background. The paper
towel will absorb excess water and iodine. (The starch of the paper towel reacts with the iodine
and causes the towel to turn black.)
7. Sketch a few of the stained onion cells in your lab notebook at high power and indicate the total
magnification of your specimen.
Part D: Human Cheek Cells
To observe living animal cells, prepare a wet mount of cells from the inside of your mouth.
1. Gently scrape the inside of your cheek with the blunt end of a toothpick. You do NOT need to see
CHUNKS OF FLESH on the tip of the toothpick to obtain a sufficient number of cells!
2. Transfer the cheek scrapings to a slide and add one or two drops of water on the slide and cover with
a cover slip.
3. On the left side of the cover slip, place a piece of paper towel folded over about 4 times. On the right
side of the cover slip add one or two drops of iodine stain.
4. Gently tilt the right side of the slide upwards to facilitate the movement the iodine across your cells
under the cover slip towards the paper towel.
5. Wash the slide by obtaining a clean piece of paper towel and a dropper bottle with water. Repeat
procedure steps 3 and 4 using water instead of iodine.
6. Examine the cells using both the low power objective (10x) and the high power objective (40X).
7. Draw and label several cheek cells at high power in page 11 of handout and indicate the total
magnification of the cells.
8. THROW THE USED SLIDE WITH HUMAN CHEEK CELLS INTO THE GLASS DISPOSAL
BOX after making your observations and sketch of cells.
Part E: Observation of Prokaryotic Cells
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Prokaryotic cells are incredibly small. For comparison purposes, you will view Escherichia coli (E.
coli) cells using the light microscope.
Obtain a slide of preserved E. coli. Begin by locating the purple stained smear using the scanning
power objective. Focus using the coarse and fine adjustment knobs before rotating the nosepiece to the
low power objective. You may want to adjust the amount of light contacting the specimen. Finally, use the
high power objective lens to view the bacteria cells. Draw what you see on page 11 of lab handout.
Part F: Observations of Other Cells & Specimens
Your teacher may provide other samples of live or preserved cells for you to look at. Observe a
variety of cells.
Preserved slide specimens may include: neurons (nerve cells), bone cells, human blood cells,
Paramecium (or other protist species), muscle cells, and sperm cells.
Live specimens may include: pond water (to view green algae, cyanobacteria, single-celled protists,
and microinvertebrate animals), tomato, rutabaga, and celery.
Analysis: Answer on separate paper (preferably typed responses) using complete thoughts and
complete sentences. You will also be graded on your pictures, so make sure they are
drawn and shaded carefully
1. Construct a Venn diagram to compare and contrast plant and animal cells.
2. Do all cells contain mitochondria? Explain.
3. Do all living plant cells contain chloroplasts? Explain citing evidence obtained from Part C of the lab.
4. Construct a Venn diagram to compare and contrast eukaryotic and prokaryotic cells.
5. What structure(s) found in plant cells are primarily responsible for cellular support? Of what
macromolecule is this material composed?
6. What are the advantages and disadvantages to an individual cell of being part of a multi-cellular
organism?
7. Describe a cellular process or task that requires three (or more) different cell organelles. Describe the
cellular process and state each organelle’s role in the cellular process.
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AP Biology
Microscope Lab Pre-Lab & Results
NAME: ________________________
Class: _________ Date: ___________
PRE-LAB
TASK #1: Label the parts numbered 1-15 (#12 is missing) of the light microscope and briefly state the
function of each Use the web URL below or Appendix D (page D-1) in your textbook to help
you.
FIGURE 7.1: A typical compound light microscope
http://www.saskschools.ca/curr_content/biology20/Library/sliced_mscope.htm
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PRE-LAB
TASK #2: Label the organelles listed on page 2-3 for the plant cell, animal cell, and prokaryotic cell
pictures below. Use the web URL (http://www.cellsalive.com/cells/cell_model.htm) or
textbook pages 100-101 to help you.
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TASK #3: PART A – Drawing of “e” from newspaper. Sketch exactly what you see in the spaces below
for the “e” viewed with the scanning power and low power objective lenses. Be as detailed as
possible! Your drawing should accurately depict the size & texture of the “e”. Calculate the
total magnification & write it below the drawing field.
Specimen: _______________________
TOTAL
MAGNIFICATION: _______________
Specimen: _______________________
TOTAL
MAGNIFICATION: _______________
*Describe, in words, the orientation of the letter when viewed through the microscope.
*How does the size of the letter change as you increase magnification?
*How does the size of the field of view change as you increase magnification?
*Using the transparent ruler, quantify the size of the field of view (FOV) at a total magnification of 40X.
*Using the transparent ruler, quantify the size of the FOV at a total magnification of 100X.
*Using the transparent ruler, quantify the size of the FOV at a total magnification of 400X.
*Name one qualitative change that occurs to the FOV total magnification increases.
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TASK #4: PART B – Draw the two different colored human hairs view using the low power objective
lens in the space below. Sketch, IN DETAIL, the size, texture, and color of the hairs. Calculate
& label the total magnification at which the hairs are viewed.
Specimen: _______________________
TOTAL
MAGNIFICATION: _______________
TASK #5: PART C – Detailed drawings of Cabomba and stained onion cells at high power.
Specimen: _______________________
TOTAL
MAGNIFICATION: _______________
Specimen: _______________________
TOTAL
MAGNIFICATION: _______________
*Label the following organelles in the drawing of Cabomba: chloroplast, cell wall, cell membrane
*Label the following organelles in the drawing of a stained onion cell: cell wall, cell membrane, nucleus
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TASK #6: PART D – Detailed drawings of human cheek epithelial cells viewed with the high power
objective lens.
Specimen: _______________________
TOTAL
MAGNIFICATION: _______________
TASK #7: PART E – Detailed drawing of E. coli bacteria viewed with the high power objective lens.
Specimen: _______________________
TOTAL
MAGNIFICATION: _______________
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TASK #8: PART F – Detailed drawings of any TWO additional specimens.
Specimen: _______________________
TOTAL
MAGNIFICATION: _______________
Specimen: _______________________
TOTAL
MAGNIFICATION: _______________
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