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Name___________________________
Date __________ Period____Group____
Lab 5.5 The Basic Unit of Life
Background:
When different types of cells are viewed under the microscope, different cell parts can be
seen. Certain living cells are best for showing parts like a nucleus or cell membrane.
Preserved cells of things that were once living are best for showing other parts like a cell wall.
Cells from producer organisms (plants) will show parts such as chloroplasts and cell walls.
Most consumer cells do not have these parts, although fungi have cell walls. We will not
consider fungi in this investigation.
Purpose: In this investigation you will:
a) observe a variety of living and once living materials under the microscope
b) determine if these materials do or do not show a cellular type of organization
c) study and located under the microscope specific cell parts like cell wall, cell
membrane, cytoplasm, nucleus, nucleolus and chloroplasts.
d) compare cell parts found in plant and animal cells
e) observe the normal appearance of Elodea cells in tap water.
f) compare normal cells in tap water to plasmolyzed cells in salt water
Procedure:
Part A: Cork Cells
Cork cells are excellent for studying a cell part common to all
plant cells. This part is the cell wall. In a cork cell, the cell wall
is easily visible. The cork is no longer living. The cell wall
remains as the only evidence of once living materials.
 Look at the picture that your teacher has provided.
The one on the left is a photocopy of the drawing of a
cork cell done by Robert Hooke in the late 1600s.
 Hooke is credited with naming the tiny compartments
“cells” because he thought they resembled the tiny cells
in which monks often lived.
 Draw a few representative cells in the space at right.
 Label the cell walls.
Part B: Human Cells
Human cheek cells may be used for viewing the cell
membrane and cytoplasm. A cell membrane is a thin outer
boundary which surrounds the cell and separates it from
neighboring cells. Cytoplasm is the jellylike inner portion of
the cell.


Gently scrape the inside of your cheek with the end of
a toothpick. You will not be able to see anything on
the toothpick when you remove it from your mouth.
Add a drop of methylene blue stain to your slide, dip
the toothpick into the stain and mix once or twice.
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Cork Cells



Add a coverslip and examine under both low and high power.
Locate and examine cells that are separated from one
another rather than those that are in clumps.
Draw several cheek cells as they appear under high
magnification. Label the cell membrane and cytoplasm.
Part C: Cell Nucleus and Nucleolus
Onion cells may be used to show a cell’s nucleus and
nucleolus. These two structures appear within most living cells.
There may be several nucleoli (plural of nucleolus) appearing as
tiny dots within each cell’s nucleus. The nucleus will appear as a
round structure inside each cell.
Human Cheek
Cells
Follow these steps in preparing onion cells for our wet mount:

Get a cut piece of onion bulb (part of the onion you eat)
snap it almost in half (Figure 12-3A).

Gently pull apart the two cut halves so that you have one
thin layer of onion tissue. (Figure 12-3B).

Place one thin onion layer onto a microscope slide.

Uncurl or unfold any overlapped portion of the cell layer.
Make sure the layer in perfectly flat. Add a drop of iodine.

CAUTION: Iodine will stain your clothing
permanently.

Add a coverslip to the stained onion carefully trying
to avoid getting air bubbles.

Observe the cells under both low and high power of
your microscope. Note the brick wall appearance of the
cells with cell walls separating the cells.

Onion Cells
Locate a small round structure, the nucleus, within
each cell. Examine a nucleus carefully by focusing up and down through the cell.

Under high power, observe the tiny dots or dark structures within the nucleus. These
are nucleoli.
The outer edge of the nucleus is made up of a thin covering called the nuclear membrane.
 Diagram a few onion cells in the space provided as they appear under high power.
 Label the cell wall, nucleus, nucleolus, and nuclear membrane.
 Clean your slide and coverslip.
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Part D: Blood Cells
Observe a prepared slide of frog blood and another one of human blood. Use low and high
power. The colors you see are not natural. Stains have been added to these cells to make
viewing easier.
 Draw several representative frog blood cells in the space provided. Use high power
but be careful to focus on low then medium then high to avoid cracking the slide.
 Draw several representative human blood cells in the space provided. Use high power
but, again, be careful to focus on low then medium then high to avoid cracking the
slide.
 Observe any differences
related to size and the
nucleus of each cell type
and include them in your
drawing.
 Label the cell wall, cell
membrane, cytoplasm
and nucleus only if these
parts are present.
Human Blood
Frog Blood
 Return the slides to the
Cells
Cells
slide tray at the front of the
room.
Part E: Chloroplasts
Another cell part found in the cells of many producers is the
green chloroplast. Elodea densa (or Anarchis), a common
water plant, shows these important structures well.
 Prepare a wet mount of an Elodea leaflet. Use the figure
as a guide.
 Using low power of your microscope, position your slide
so you are looking near the edge of the leaflet. Locate
green, oblong cells. Examine these cells under high
power.
 Note the small green organelles inside each cell. These are
chloroplasts. Movement of the chloroplasts within the cell
often can be observed. Attempt to locate moving
chloroplasts.
 Diagram a single Elodea cell in the space provided.
Use high power.
 Label cell wall and chloroplast.
 Keep this slide for use in Part F of the lab.
Normal Cell Wall
Part F: Normal vs. Plasmolyzed Cells
(Elodea in fresh water)
Diffusion of water molecules across a cell’s outer membrane
from areas of high water concentration to areas of low water concentration is called osmosis.
This movement of water may be harmful to cells. It can result in cell water loss (plasmolysis)
when living cells are placed into an environment where the water concentration inside the cell
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is higher than outside the cell. However, most cells live in an environment where movement
of water in and out of the cell is about equal. Therefore, there are no harmful effects to the
cell.
Procedure
 On the same slide you used in Part E, you’ll add another
Elodea leaflet. Use the Figure as a guide.
 Step 1. Near your other Elodea leaflet (but not touching it),
add a fresh Elodea leaflet.
 Step 2. Put one drop of 6% salt water on the leaflet. Add a
coverslip carefully trying to avoid any air bubbles.
NOTE: Make sure that the two liquids on the slide do not run together or touch each other. If
they do, discard leaves and start over using fewer drops of liquid.
 Wait two or three minutes. Observe each leaf under both low
and high power lenses. To observe both leaves, simply move
the slide back and forth across the microscope stage.
 Carefully observe the location of chloroplasts in relation to the
cell wall of both leaves.
 Diagram in the space provided a single cell from each side. Label
the cell wall, cell membrane, and chloroplasts in both cells. (Be
careful—can you see the cell membrane in both cells or only in
one?)
Plasmolyzed cell
(Elodea in salt water)
Analysis Questions
Analysis - Part A:
1) Is the cork you drew alive?
2) What are the small units that can be seen under high power called?
3) Do these units appear filled or empty?
4) What specific part is all that is left of the cell?
5) In 1665, Robert Hooke, an English scientist, reported an interesting observation while
looking through his microscope at cork. “I took a good clear piece of cork, and with a
penknife sharpened as keen as a razor, I cut a piece of it off, then examining it with a
microscope, me thought I could perceive it to appear a little porous, much like a
honeycomb, but that the pores were not regular.”
a. What were the honeycomb units at which Hooke was looking?
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b. What specific cell part was left of the cork?
6) Is cork produced by a plant or an animal?
a. Do animal cells have cell walls?
7) Use your text (or remember from chapter 4) and determine the name of the chemical
which makes up the cell wall.
Analysis - Part B:
1) Describe the shape of a cheek cell.
2) Are cheek cells produced by plants or animals?
b. Is a cell wall present?
3) Are cheek cells alive?
4) Describe the location of the cell membrane.
5) Use your text to determine the function of the cell membrane.
a. What is the cell membrane made of? ______________________________
6) a. Describe the location of the cell’s cytoplasm.
b. Describe the appearance of the cell’s cytoplasm.
7) Use your text to determine the function of the cytoplasm.
8) Why was a stain added to the cheek cells?
9) Do you have evidence that living things (or once-living things) are composed of basic
units called cells? Explain.
______________________
_________________________________________________________________
Analysis - Part C:
1) Describe the shape of an onion cell.
2) a. Are onion cells produced by plants or animals?
b. Is a cell wall present?
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3) a. Describe the shape of the nucleus of an onion cell.
c. Within what part of the cell already studied does the nucleus lie?
4) What is the function of a cell’s nucleus?
5) a. Describe the shape of the nucleolus of an onion cell.
a. Where is the nucleolus found?
b. What is the function of a cell’s nucleolus?
6) What structure separates the contents of the nucleus from the cytoplasm?
7) Why were the cells stained?
Analysis - Part D:
1) Describe the shape and size of the frog blood cell. ___________________________
2) Describe the shape and size of the human blood cell on the same magnification as the
frog blood cell._________________________________________________________
3) Are there any structures visible in one type of blood cell that were not in the other
blood cell type? ________
a. What are these structures? _______________________________________
b. What does this mean? (Hint: think of what is inside this missing structure and
what it can’t do as a result.) _______________________________________
4) Are blood cells from a producer or consumer? ______________________________
5) What cell part name is used to describe the outer edge of both blood cell types?
___________________________________________________________________
Analysis - Part E:
1) Describe the shape of an Elodea cell.
2) a. Is Elodea a plant or an animal?
a. Is a cell wall present?
3) Describe the:
a. color of the chloroplasts.
b. shape of the chloroplasts.
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4) Within what part of the cell do chloroplasts lie?
5) What is the function of the chloroplast?
6) Are chloroplasts typically found in consumer cells? ______________ Explain
_____________________________________________________________________
_____________________________________________________________________
Analysis - Part F:
1) Describe the location of chloroplasts in a normal Elodea cell (in tap water).
_____________________________________________________________________
2) Describe the location of chloroplasts in a plasmolyzed cell (in salt water). __________
_______________________________________________________________________
Read the following four statements before answering the questions:
a) Elodea cells normally contain 1% salt and 99% water inside their cell.
b) Tap water used in this investigation contains 1% salt and 99% water.
c) Salt water used in this investigation contains 10% salt and 90% water.
d) Salt water has a higher concentration of salt than fresh water or Elodea cells.
3) Answer the following questions about the Elodea cell in tap water.
a. What is the percentage of water outside the cell (in the tap water)? __________
b. What is the percentage of water inside the cell? ________________________
c. How do the percentages compare? __________________________________
d. Did the cell change shape? Explain. __________________________________
4) Answer the following questions about the Elodea cell in the salt water.
a. What is the percentage of water outside the cell at the investigation’s start? ___
b. What is the percentage of water inside the cell at the investigation’s start? ____
c. Is the percentage of water (concentration) inside higher or lower than the
percentage outside? _____________________________________________
d. When will water move across the cell’s membrane? ______________________
5) Circle the direction water should move: from high to low or low to high concentration.
6) Did the inside of the cell change shape due to water loss? Explain. _______________
_____________________________________________________________________
7) What is plasmolysis? ___________________________________________________
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Analysis General
Complete the following chart. Indicate, by using a check mark, each structure contained in a
plant or animal cell. If the structure is absent, there won’t be a check mark.
Nucleus
Cell
Wall
Cytoplasm
Nuclear
Nucleolus Chloroplasts
Cell
Membrane
Membrane
Animal
Cell
Plant
Cell
Complete the “typical plant cell” drawing below. Use your text and class notes to help you
draw and label the following organelles. Some are already drawn for you.
Vacuoles
Mitochondria
Golgi bodies
Endoplasmic reticulum
Ribosomes
Lysosomes
Cell wall
Cytoplasm
Cell membrane
Chloroplast
Nucleus
Nucleolus
Complete the “typical animal cell” drawing below. Use your text and class notes to help you
draw and label the following organelles.
Mitochondria
Centrioles
Golgi bodies
Endoplasmic reticulum
Ribosomes
Lysosomes
Cytoplasm
Cell membrane
Nucleus
Nucleolus
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