WISE 2007-2008
Plant Cells – Laboratory Activity
Purpose: To compare the structures and organelles of two
typical plant cells – onion and elodea.
Biologists are always interested in studying cells.
They want to know how different organisms function and how
they’re organized. From their observations, biologists created
the cell theory. The cell theory says that the cell is a structural
and functional unit of living things. Cells contain structures
called organelles that carry out life processes. Certain cells
contain different organelles as you will see in this lab.
A typical plant cell contains many different parts, such as the nucleus, mitochondria,
chloroplast, vacuoles, cell wall, cell membrane, endoplasmic reticulum, and Golgi apparatus.
The nucleus is the cell’s control center – it contains the DNA that tells the cell what to do and
how to do it. Vacuoles are used to store the cells food and waste. The endoplasmic reticulum and
the Golgi apparatus help to move different molecules around the cell. Mitochondria are the cell’s
powerhouse – they provide the cell with most of its energy. The cell wall and the cell membrane
protect the cell from harmful things in its surroundings. The cell wall – a hard layer – provides
the cell with structural support.
Chloroplasts use light, water, and carbon dioxide (CO2) to undergo photosynthesis. As a
result of photosynthesis, the plant cell gives off oxygen (O2) and gets sugar for energy.
Chloroplasts contain chlorophyll, which absorbs all but green light for photosynthesis – that’s
why we see plants as green!
In this lab, we will look at onion and elodea cells to see what plant cells look like up
close. Stains like methylene blue help us to see various structures, or organelles, within a cell.
CAUTION! Be careful not to get these stains on your clothing or skin. If you get any stain on
your skin, wash your hands. Also, be sure to handle the glass slides and cover slips carefully so
they don’t break.
Materials: Onion cell slices, elodea cells, droppers, methylene blue, water, slides, cover slips,
tweezers, paper towels, microscopes.
Onion cells
Part I. Onion Cells
1. Take a small, thin piece of onion, and using tweezers, peel off the thin, transparent
membrane tissue from the underside (the rough side).
2. Lay the membrane flat on the center of a clean glass slide and add one drop of water and
one tiny drop of methylene blue.
3. Wait 30 seconds.
4. Place the cover slip on top of the water drop by slowly lowering it on at an angle to
prevent air bubbles from forming.
WISE 2007-2008
5. Place the edge of a paper towel against one edge of the cover slip and add a drop of water
to the opposite edge of the cover slip. The paper towel should absorb the extra stain and
pull the water through the sample.
6. Make sure the lowest power lens (the shortest one) is in line and that the microscope light
is turned on. Place the prepared slide onto the stage of the microscope. Focus until you
can see your sample clearly.
7. You should see lots of onion cells, like rectangles stacked together. Draw what you see in
the box labeled “onion – low-power magnification.”
8. Carefully switch to a higher powered lens and focus again so that you can see a closer
view of the cells.
9. You should be able to see several onion cells up close. Draw what you see in the box
labeled “onion – high-power magnification.” Can you see the cell wall, cell membrane,
nucleus, cytoplasm, or a vacuole? Label any organelles you can identify.
10. Clean the cover slip and slide off with water and dry them when you are finished.
Questions:
What is the shape of an onion cell?
How are the onion cells arranged?
What parts of the onion cells absorbed the stain?
Part II. Elodea Cells
Elodea is a group of water plants with very thin leaves commonly used in aquariums.
Elodea cells
1. Place a piece of an elodea leaf on a slide, add a drop of water, and carefully put a cover
slip on top of it to avoid air bubbles.
2. Using the low-powered lens of the microscope, focus on one layer of the leaf.
3. You should see lots of elodea cells stacked together like bricks. Draw what you see in the
box labeled “elodea – low-power magnification.”
4. Carefully switch to a higher powered lens and focus again so that you can see a closer
view of the cells.
5. You should be able to see several elodea cells up close. Draw what you see in the box
labeled “elodea – high-power magnification.” Can you see the cell wall, cell membrane,
nucleus, cytoplasm, vacuoles, and chloroplasts? Label any organelles you can identify.
6. Can you find a cell in which cytoplasmic streaming is occurring? This is when cytoplasm
moves around the large central vacuole of the cell. Chloroplasts use cytoplasmic
streaming to move to the best position in a cell in order to get the most light for
photosynthesis.
7. When you are finished, clean the cover slip and slide off with water and dry them.
Questions:
How are the onion and elodea cells similar? What parts did they have in common?
How are the onion and elodea cells different?
Answers:
Both the onion and elodea cells have a cell wall and cytoplasm, but the onion cells did not have
any chloroplasts.