Download Onion Rings - Moore Public Schools

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control center of the cell and regulates all the processes
that occur within the cell. Some of the important structures of the plant cell are the cell wall which provides
support and protection, the cell membrane which allows dissolved material to enter and leave the cell, and
cytoplasm, the fluid that fills each cell in which other
important cell parts can be found.
What you will be able to see in either a wet mount or a
stained, wet mount onion skin slide will depend upon the
magnifying power of your microscope and the quality of
the wet mount slides. The basic cell shape will be visible
in good wet mount slides viewed at even 20X.
Topic
Onion cells
Key Question
What structures can be observed in onion cells?
Focus
Students will make a wet mount slide of onion cells and
observe the cell walls. Students will stain a wet mount
slide of onion cells and observe an onion cell’s nucleus,
cytoplasm, cell wall, and cell membrane.
Guiding Documents
NCTM Standards
• Use mathematics in other curriculum areas
Management
1. This activity will take about two 45-minute periods.
2. It is suggested that the teacher review the procedure
for preparing a wet mount slide with students.
3. Cut each onion in half and soak in half-filled cups
of water over night. This makes it easy to separate
the onion’s membrane.
4. Have tweezers, eyedroppers, water, and methylene
blue stain ready.
5. When the students are ready to stain the onion slide,
have them do this at special stations located around
the room. Put dropper bottles of stain in tip proof
boxes and set these boxes on newspaper.
Project 2061 Benchmarks
• Know why it is important in science to keep honest, clear, and accurate records.
• Microscopes make it possible to see that living
things are made mostly of cells.
• All living things are composed of cells, from just
one to many millions, whose details usually are
visible only through a microscope.
Math
Ratio and proportion
Geometry and spatial sense
Procedure
Preparing the wet mount slide of onion skin
1. Have students clean the slide and cover slip.
2. Direct them to break an onion slice in two.
3. Tell them to carefully pull the slice apart.
4. Have them use tweezers to pull off a very thin piece
of onion skin.
5. Direct the students to place the skin in the center
of their slide. Urge them to try to keep it from folding and to flatten it as much as possible.
6. Have them add a drop of water to the onion skin
and cover with a cover slip.
7. Tell them to press the cover slip down carefully to
remove any air bubbles.
8. Have students place the slide on the stage of the
microscope, set it to low power, adjust the focus
so the onion slice is clear, and draw four or five
cells as they see them. Have them label the
cell walls.
9. Direct them to switch to high power and try to
identify the cell membrane, nucleus, and cytoplasm.
Science
Life science
cells
Integrated Processes
Observing
Recording data
Comparing and contrasting
Applying
Materials
Whole white onion
Microscope
Microscope slide
Plastic cover slip
Methylene blue (1% solution, see Resource Section)
Dropper bottle with eyedropper
Tweezers
Background Information
Although cells vary in size and shape, most have a
similar cellular organization. The nucleus is the most
prominent feature of a plant cell. The nucleus is the
MAGNIFICENT MICROWORLD ADVENTURES
Staining the onion cells
1. Have students lift up the cover slip and add one or
two drops of methylene blue to the slide.
48
© 1995 AIMS Education Foundation
2. Direct them to lower the cover slip and examine
the cells on high power.
3. Methylene blue stains different parts of the cells
so that they can see structures they could not see
before. Have the students draw lines from the labels
(cell wall, cell membrane, cytoplasm, and nucleus)
to the appropriate structures in their drawing.
11. Why are onion cells more like squares and rectangles
than ovals? [The cells “fit together” without gaps at
the corners. This makes the cells stronger.]
Extensions
1. Have the students make wet mount slides using
red and green onions. Compare the cell shapes.
2. Prepare wet mount slides of other plant cells (i.e.,
carrots or geraniums).
Discussion
1. What is the general shape of the onion cells?
[rectangular]
2. Describe what you saw without the stain.
3. Why do you think there are many cells close
together? [strength and protection]
4. Is the onion skin composed of one cell or many
cells? [many cells]
5. Why is it easier to see the onion cells after they are
stained with methylene blue? [The stain creates
contrast between light and dark structures.]
6. All plant cells have cell walls. What is the function of
the cell wall? [to provide strength and protection]
7. Can you see a line on the inside of the cell walls?
(probably not) What is this structure’s name? [the
cell membrane] What is its function? [allows dissolved materials to enter and leave the cell]
8. Each cell has a control center. What is the control
center called? [the nucleus]
9. Count the number of cells that are seen in the field
of view under low power magnification and also
high power magnification. Compare the number of
cells observed in each field of view. Express these
numbers as a ratio. For example, if you can see six
cells under low power and two cells under high
power, then the ratio is 6 : 2 or 3 : 1.
10. How many sides does an onion cell usually have?
[four] What geometric shapes may be similar to
the onion cell’s shapes? [four-sided polygons]
MAGNIFICENT MICROWORLD ADVENTURES
What You Should See
Onion Rings
Bausch & Lomb
Elementary School
Microscope
Brock Optical
Magiscope ®
20 X
25 X
Learning Things, Inc. Radio Shack ®
Super Microscope
50 X
49
Micronta ®
100 X
© 1995 AIMS Education Foundation