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2.1 OBSERVING PLANT AND ANIMAL CELLS
Time required: 2 double periods
Name:___________
Introduction: Cells are the structural and functional units of life. All organisms are composed of cells,
whether they exist as single cells, colonies of cells, or in multicellular form. There are two general types of
cells: prokaryotic and eukaryotic. Prokaryotic cells are very tiny and do not have a membrane-bound nucleus
and cell organelles. Bacteria and blue-green algae (cyano bacteria) are prokaryotes. Eukaryotic cells (protists,
fungi, plants, animals) are usually larger, contain a membrane bound nucleus and cell organelles such as
plastids, mitochondria, lysosomes, and Golgi complexes. Non-membrane-bound organelles, such as ribosomes
and centrioles are also present in eukaryotic cells. Cells are small because as they get larger, their surface area
to volume ratio becomes too small to bring in enough nutrients and get rid of enough wastes for survival. This
surface area to volume ratio can be considered the “efficiency” of the cell. The more chemically active a cell
is, the more efficient it must be. The most active cells will tend to be small. In this investigation, you will use a
compound light microscope to examine a variety of plant and animal cells.
Learning outcome: After completing this experiment, students will be able to identify different cell
organelles in various plant and animal cells. They will also be able to note the differences between animal and
plant cells
Group size: 2 per group
Objectives:
1. To examine and identify cell organelles in different plant animal cells.
2. To identify similarities and differences between plant cells and animal cells.
Pre-lab activity: Read the instructions given for this investigation and write the definitions of key terms.
Key terms: Eukaryote, prokaryote, plastid, chloroplasts, chromoplasts, leucoplasts, vacuole, cell wall,
cytosol, epidermis, nucleus, plasma membrane, unicellular organism and multicellular organism
Apparatus and materials per group:
Compound light Microscope
Glass Microscope Slides
Cover slips
Lens tissue
Camel hair brush
Microscope lamp
Lens solution
Millimeter ruler
Pasteur pipette
Small plastic ruler
Distilled water
Methylene Blue stain
Lugol’s iodine solution (I2KI)
Lab coat
Scissors
Paper towel
Tooth picks
Large beaker with bleach
200 ml beaker with water
Lab coat
Onion scale
Elodea leaf
A piece of red pepper
A piece of potao
Prepared slides of human blood cells
Prepared slide of cheek cells
Prepared slides of frog blood cells
Dissecting probe
Sharp razor blade
Forceps
PART A- PLANT CELLS
Plant cells are eukaryotic and contain both a membrane-bound nucleus and membrane-bound organelles. A cell
wall composed of cellulose surrounds the plant cell. A large central vacuole surrounded by a membrane (the
tonoplast) is used for storing water, pigments, and wastes. Within the cytoplasm are membrane-bound
organelles called plastids. There are there types of plastids: chloroplasts, leucoplasts and chromoplasts.
Chloroplasts contain chlorophyll which traps sunlight for photosynthesis. Chromoplasts contain several types
of pigment which give plants an orange or yellow color. Leucoplasts are colourless and store starch.
CAUTION:
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Handle all glassware and sharp tools carefully.
Always handle the microscope with extreme care.
If you are using a microscope with a lamp, follow all safety rules related to electrical equipment.
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Use caution when handling microscope slides and cover slips as they can break easily and cut you.
1. Onion Epidermal cells
Nucleus
Cytoplasm
Cell wall
From yr 11 CD p 81
Figure 1: Onion cell
Method:
Note: One average-sized onion cut into 1cm2 will be sufficient for a class. An onion scale is lined on either
side by a single layer of cells called an epidermis.
1. Collect the microscope, microscope lamp and other materials required and place them on your table.
2. Take an onion scale and peel the inner skin using a forceps as shown in figure 2a.
3. Spread out the skin as smoothly as possible on a microscope slide.
Note: If the epidermis becomes folded on the slide, use a dissecting probe to gently unfold and flatten it.
4. With a dropper, place a drop of water on top of the onion skin.
5. Using a mounted needle place the cover slip on the onion skin as shown in figure 2b. Place a small piece of
paper towel on one edge of the cover slip and draw off some of the water until the cover slip adheres tightly to
the slide.
Figure 2b- Making a wet mount Figure 2c – Staining the onion
from Biozone CD p 76
cells- From Biozone CD p 76
Figure2- Steps in staining an onion cell
6. Examine the tissue with the low power objective. Note the shape of the cells as well as any structures within
the cell (in the cytoplasm).
7. Remove the slide and carefully draw off the water by placing a piece of paper towel at one side of the cover
slip.
8. With the dropper, place a drop of iodine solution at the edge of the cover slip and draw in the stain using a
piece of paper towel or filter paper on the opposite edge as shown in figure 2c. Observe parts of the cell that are
stained.
CAUTION: Lugol's iodine solution is an irritant poison. Avoid skin/eye contact; do not ingest. Flush
spills and splashes with water for 15 minutes and rinse mouth with water. Call your teacher.
9. Repeat steps 6-8 with a different slide with onion skin. This time add a drop of Methylene Blue stain to one
edge of the cover slip and draw under with a piece of paper towel on the opposite end. Observe what structures
are stained in the onion epidermal cells. Notice how staining with Methylene blue affects the cell compared
with cells that were stained with iodine.
10. Use high power objective to observe unstained and stained onion cells taking care not to touch the slide with
the objective.
11. Identify the cell wall, cytoplasm, nucleus and vacuole. You may be able to see a nucleolus within a
Figure 2a- Peeling onion skin
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nucleus.
12. Estimate the length in microns of an onion cell as seen under high power.
a) To do this measure the diameter of the field of view by placing a transparent plastic ruler on the slide.
b) Count the number of cells that fit across the diameter of the field.
c) Divide the diameter by the number of cells
Length of an onion cell = Diameter of field of view = ________x1000=________micrometers
Number of cells
e.g. Suppose that a typical cell is approximately 1/3 the diameter of the field of view and the field of view is
0.45 mm then the cell is 0.45 /3 = 0.15mm or 1.5x100= 150 micrometers
13. Clean the slide with water and wipe with a paper towel. Dispose of the onion scale in a container.
Results: Draw stained and unstained onion cells as viewed under high power objective. (x 400)
Label the following: cell membrane, cytoplasm, cell wall, vacuole, nuclear membrane, nucleus and nucleolus
Unstained onion cells - x 400
Stained onion cells - x400
Discussion questions:
1. Which cell organelles did you see in an unstained onion cell?
Cell wall, cytoplasm and nucleus were seen in an unstained onion cell.
2. Did you observe any difference between onion cells stained with Lugol’s iodine and methylene blue stain?
The nucleus was stained dark blue and was clearly visible with methylene blue satin
3. Which cell organelles were not visible under light microscope?
Ribosomes, endoplasmic reticulum and Golgi body were not visible under light microscope.
4. Did you see nucleolus?
After staining nucleolus was visible in some cells.
5. What is the length of an onion cell? The length of an onion cell is 150 micrometers (answers may vary)
6. What is the general shape of the onion cells? It is rectangular in shape.
2. Elodea leaf cells
Elodea plants can be obtained from aquarium shops. Keep them in water and sunlight. Cut healthy leaves from
the growing tips. These cells contain numerous chloroplasts. Chloroplasts contain chlorophyll which traps light
energy during photosynthesis to make glucose. Cytoplasmic streaming, also called cyclosis, transports
nutrients, enzymes, and chloroplasts, enhances the exchange of materials between organelles. Cyclosis can be
seen clearly in elodea leaves. Since there is a large vacuole in elodea cells, you will see chloroplasts moving
around the vacuole.
Figure 3: Elodea cells From Biozone CD p81- Label the parts
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Method:
1. Place a drop of water on a clean slide and put an elodea leaf on top of the water drop. Place a cover slip on
top of the leaf using a mounted needle.
2. Observe the cells under low power first and then under high power.
3. Look closely at the chloroplasts located near the tip of the leaf and see if they are moving. If not wait for a
minute because the bright light and warmth of the lamp encourages cytoplasmic streaming.
Note: You should find cells in which the chloroplasts are moving around the perimeter of the cells. This
movement is the result of cytoplasmic streaming or cyclosis. Due to the thickness of the cells, you will have to
continually focus up and down to see all the parts. This is an example of the concept of the depth of focus.
4. Stain the elodea cells with Lugol’s iodine solution. View the cells under high power objective and note the
change in the colour of chloroplasts after adding the stain.
Note: cell die after adding the stain and cytoplasmic streaming stops.
5. Identify the cell wall, cytoplasm, nucleus, chloroplasts and the vacuole.
7. Calculate the size of one elodea cell by following step 13 from onion cell investigation.
8. Clean the slide with water and wipe with a paper towel. Dispose of the elodea leaf in a container.
Results: Draw stained and unstained elodea cells as viewed under high power objective. (X 400)
Label the following: cell wall, cytoplasm, cell wall, vacuole, nucleus and chloroplasts
Unstained elodea cells - X 400
Stained elodea cells - X400
Discussion questions
1. Describe the general shape of elodea cells.
Elodea cells are rectangular in shape with rounded edges
2. What was the estimated size of an elodea cell?
The average size of an elodea cell is about 50 um
3. What makes elodea cells so green?
The presence of chloroplasts makes elodea cells green
4. What role do chloroplasts play during photosynthesis?
Chloroplasts use light energy to synthesize glucose during photosynthesis
5. What parts of the cell were most obviously stained by the iodine? Why do you think this was?
Iodine reacts with starch and turns blue black in colour. Chloroplasts turned blue black because
they contained starch.
6. Did you observe cytoplasmic streaming in elodea cells?
Cytoplasmic streaming was observed in elodea cells. (Some students may not see this)
7. Why do you think the chloroplasts moved only around the edges of the cells?
Chloroplasts moved only around the edges of the cells because they were moving around a large
vacuole.
8. What is the purpose of cytoplasmic streaming?
Cytoplasmic streaming carries chloroplasts and other organelles from one part of the cell to
another. This circulation positions the chloroplasts so that they can absorb the maximum amount of
sunlight for photosynthesis
9. List the similarities and differences between Elodea cells and onion cells.
Both onion and elodea cells had cell wall, cell membrane, cytoplasm, vacuole and nucleus.
Chloroplasts were present in elodea cells but were absent in onion cells.
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3. Potato tuber cells
Potato plants produce and store starch in special organelles called plastids. Plastids that store starch are called
leucoplasts or amyloplasts. Potato cells do not contain chloroplasts because potato tuber grows under ground.
Since iodine stain makes starch turn blue black, the starch grains
in leucoplasts can easily be viewed with a compound
microscope.
Method:
Cytoplasm
1. Use a razor blade to slice a piece of potato as thin as possible.
Caution: Be careful not to cut your fingers.
2. Prepare a wet-mount slide by using a drop of water.
3. Study the slide at low power (10X objective) and then at high
power (40X objective).
4. Add a drop of Lugol's iodine solution to the side of the cover
slip and observe the cells as the iodine solution makes contact
with them.
Figure 4- Stained potato cells
from http://waynesword.palomar.edu/lmexer1.htm#potato
Note: The black areas are starch grains being stored in the leucoplasts. Two or three grains will be
surrounded by the cell wall of the potato cell.
5. Identify the cell wall, cytoplasm and leucoplasts
7. Clean the slide with water and wipe with a paper towel.
8. Dispose of the potato slice in a container
Results: Draw stained and unstained potato cells as viewed under high power objective(X 400)
Label the following: cell wall, cytoplasm and leucoplasts.
Unstained potato cells - X 400
Stained potato cells - X400
Discussion questions
1. Did you see any chloroplasts in potato cells? Why or why not?
Potato cells do not contain chloroplasts because potato tuber grows underground and does not
photosynthesise
2. Why did leucoplasts turn blue black after adding Lugol’s iodine solution?
Iodine solution reacts with starch and produces blue black colour. As
leucoplasts in potato cells contain starch grains, they turn blue black when
iodine was added.
4. Red pepper cells
Red pepper cells contain chromoplasts which give reddish orange colour to
these cells
Method:
Figure 5- Red pepper cells
1. Use a razor blade to slice a piece of tissue, as thin as possible and
scrape some tissue from the red pepper slice.
from www.uri.edu
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2. Prepare a wet-mount slide using water.
Note: You should be able to see chromoplasts which are reddish in colour
3. Add Lugol’s iodine solution and note the changes in the colour of cell organelles.
4. Identify the cell wall, cytoplasm and chromoplasts and note the shape and colour of the cells.
5. Clean the slide with water and wipe with a paper towel. Dispose of
the red pepper tissue in a container
Results: Draw unstained red pepper cells as viewed under high power objective(X 400)
Label the following: Cell wall, cytoplasm and chromoplasts
Unstained red pepper cells - X 400
Stained red pepper cells - X400
Discussion questions:
1. Which organelles were seen in red pepper cells?
Chromoplasts were seen in red pepper cells.
2. What is the function of these organelles?
Chromoplasts contain red colour pigment and make the vegetable red in colour.
Did you find leucoplasts and chloroplasts sin red pepper cells?
Leucoplasts and chloroplast were not found in red pepper cells
PART B- ANIMAL CELLS
Animal cells are heterotrophic eukaryotic cells which do not have cell walls, plastids and large vacuoles. They
have membrane bound nucleolus and cell organelles such as mitochondria, ribosomes and Golgi bodies. Red
blood cells do not have nuclei but white blood cells have large nuclei.
1. Human cheek cells
Method:
1. Place the prepared cheek cell slide on the stage of the microscope and
observe the slide first with low power objective and then with high power
objective.
2. Observe the cell membrane, cytoplasm and nucleus and draw 2
diagrams and label the parts.
3. Calculate the size of cheek cells in micrometers as explained in the
onion slide method (step12)
Figure6- Cheek cells
from http://waynesword.palomar.edu/lmexer1.htm#potato
Results: Draw unstained cheek cells as viewed under high power objective(X 400)
Label the following: cell membrane, cytoplasm, nucleus and nucleolus if visible.
stained cheek cells - X 100
Stained cheek cells - X400
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Discussion questions:
1. What is the shape of cheek cells? Cheek cells are irregular in shape.
2. What is the estimated size of a cheek cell? The estimated size of a cheek cell is 77micrometers
3. Which organelles were visible in cheek cells?
Cell membrane, cytoplasm and nucleus were visible in cheek cells.
4. Explain why a cell wall and chloroplasts were not found on the cheek cells.
Since cheek cells are animal cells, they do not have cell walls and chloroplasts.
5. What is the function of cheek cells?
They form a lining of the mouth and protect the underlying cells from enzymes produced in the mouth.
6. Why do you think that cheek cells need to be constantly replaced?
Cheek cells are replaced constantly because, they are exposed to mechanical and chemical digestion in the
mouth
2. Human and frog blood Cells (prepared slides).
Human red blood cells are round in shape and lack nuclei. Frog red blood cells are oval in shape and contain
nuclei. Red blood cells carry oxygen from the lungs to cells. Human white blood cells are irregular in shape and
have nuclei. White blood cells engulf micro organisms by phagocytosis and destroy them
Method:
1. View the human blood slide first under low magnification and then turn to higher magnification.
Note: You will see both "purple" and "pink" stained cells. The "pink" cells are red blood cells. The
"purple" cells are white blood cells. You may have to hunt for the white blood cells.
2. Draw what you observe and label the drawing properly.
3. View frog’s blood cells under low power and high power objectives
4. Draw what you observe and label the drawing properly.
Red blood cell
with nucleus
White blood
cells with
nucleus
Red blood
cells without
nucleus
Figure 7- Human blood cells
from Biozone CD p 76
Figure 8-Frog blood cells
http://www.biocraftscientific.com/products/slides_zoology.htm
Results: Draw human and frog blood cells as viewed under high power objective(X 400)
Label the following: cell membrane, cytoplasm and nucleus
Human blood cells - X 40
Frog blood cells - X40
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Discussion questions:
1. What evidence do you have that human blood is not made of plant cells?
Human blood cells do not have cell wall, vacuole and chloroplasts
2. Describe the shape of the red blood cells and white blood cells.
Human red blood cells are round in shape and lack nuclei. White blood cells are large and irregular in
shape and have large nuclei
3. What is the function of each type of blood cell?
Red blood cells carry oxygen and white blood cells engulf bacteria and viruses
4. How are frog’s red blood cells different from human red blood cells?
Frog red blood cells have nuclei where as human red blood cells lack nuclei.
General discussion questions
1. How do you know if a cell is a eukaryotic cell or a prokaryotic cell?
Prokaryotic cells do not have membrane bound nuclei and cell organelles. Eukaryotic cells have
membrane bound nuclei and numerous membrane bound cell organelles
2. What types of organisms possess eukaryotic cells?
Protists, fungi, plant and animals possess eukaryotic cells.
3. Compare the similarities and differences between all the plant cells you observed
Plant cells
Shape
Cell structure
Cell wall Cytoplasm Nucleus Nucleolus Vacuole
Plastids
Onion
Rectangular
yes
yes
yes
yes
yes
no plastids
Elodea
Potato
Red pepper
Rectangular
Rounded
Rounded
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
chloroplasts
leucoplasts
chromoplasts
4. Which of the structures are unique to plant cells?
Plant cells have cell walls, plastids and large vacuoles.
5. Which structures are common to both plant and animal cells?
Both plant and animal cells have cell membrane, cytoplasm and nucleus
6. Which plant cells have chloroplasts?
Only plant cells that photosynthesise have chloroplasts.
7. In which cells did you see cytoplasmic streaming?
Cytoplasmic streaming was seen in unstained elodea cells
8. Identify the structure you found in the animal cells that you observed by placing a tick, cross or a question
mark if you are not sure.
Animal cells
Shape
Cell structure
Cell
Cytoplasm Nucleus Nucleolus Vacuole Plastids
membrane
Cheek cells
Irregular
yes
yes
yes
yes
no
no
Human RBC
Round
yes
yes
no
yes
no
no
Human WBC
Irregular
yes
yes
yes
yes
no
no
Frog RBC
Round/
yes
yes
yes
yes
no
no
oval
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9. Identify cell structures in the diagram given below:
a) Cytoplasm
b) Vacuole
c) Starch grains
d) Chloroplast
e) Mitochondrion
f) Cell wall
g) Chromosomes
h) Nucleus
i) Nuclear membrane
j) Cell membrane
Figure 9- Generalised diagram of a eukaryotic cell as seen through TEM From Biozone Cd p 84
10 . List the similarities and differences between the plant cells and the animal cells you have observed.
Structures
Plant cells
Animal cells
Cell wall
Yes
No
Cell membrane
Yes
Yes
Cytoplasm
Yes
Yes
Nucleus
Yes
Yes
Vacuole
Large
No
Plastids
Yes
No
Conclusion:
1. Briefly summarise the differences between plant cells and animal cells.
Plant cells have a cell wall, plastids like chloroplasts, chromoplasts and leucoplast. They also have large
vacuoles. Animal cells do not have a cell wall and plastids. They do not have large vacuoles.
2. What are the advantages and disadvantages of staining cells?
When cells are stained, the cell organelles are visible more clearly but the cells die due to the toxicity of the
stains.
3. List the advantages and disadvantages of using compound light microscopes?
The highest magnification under compound light microscopes is 0nly 400 x. There fore it is not possible to
see small cell organelles such as ribosomes, endoplasmic reticulum and Golgi body. The main advantage is
living cells can be seen when they are not stained
Web sites:
http://www.sinauer.com/cooper/4e/videos0103.html - video of cytoplasmic streaming
http://waynesword.palomar.edu/lmexer1.htm#potato
http://waynesword.palomar.edu/lmexer1.htm#potato
http://www.biocraft-scientific.com/products/slides_zoology.htm
www.uri.edu
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