Download Comparing Plant and Animal Cells

1.4 Inquiry Investigation
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Comparing Plant and Animal Cells
You have learned about some of the structures inside plant and animal
cells. In this investigation you will examine plant and animal cells
under a microscope. Being able to identify cell structures is important
in understanding their functions.
Question
How do plant cells differ from animal cells?
Hypothesis
If a microscope is used, then plant cells can be differentiated from
animal cells by their structures.
Experimental Design
In this investigation you will prepare a wet mount of onion cells. You
will use the slide to identify structures within plant cells. You will use a
prepared slide to examine the parts of an animal cell.
Procedure
1 Using a knife, your
teacher will remove a
small section (about
2 cm2) from an onion.
• Use tweezers to remove a
single layer from the
inner side of the onion
section. If the layer you
removed is not translucent
to light, then try again.
Iodine will irritate eyes, mouth,
and skin. It may stain skin and
clothing. Do not touch the stain
with bare hands, and do not
touch your face after using the
stain.
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Unit 1
2 Place the onion skin in
the centre of a slide. Make
sure the skin does not fold
over.
• Place two drops of water
on the onion skin.
• From a 45 ˚ angle to the
slide, gently lower a cover
slip over the onion skin,
allowing the air to escape.
This is called a wet mount.
• Gently tap the slide with
the eraser end of a pencil
to remove any air bubbles.
Materials
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onion
tweezers
microscope slide
medicine dropper
water
cover slip
light microscope
safety goggles
rubber gloves
iodine stain (Lugol’s)
paper towel
lens paper
prepared slide of human
epithelium (skin cells)
3 Place the slide on the
stage and focus with the
5A low-power objective lens
in place.
• Move the slide so the cells
you wish to study are in
the centre of the field
of view.
• Rotate the nosepiece of
the microscope to the
medium-power objective
lens and use the fineadjustment knob to bring
the cells into view.
(a)Draw and describe
6C what you see.
SKILLS HANDBOOK: 5A Using the Microscope 6C Scientific & Technical Drawing
Exploring
1. Do the cells of bananas and
green peppers have the same
shape as the onion cells? A
toothpick can be used to
scrape cells from a banana or
a green pepper.
(a) Devise a technique that
allows you to view these
cells.
(b) Describe the technique.
(c) Are all plant cells the same?
Figure 1
By looking at cells under a
microscope, you can tell if they
came from a plant or an animal.
5 Switch to low power.
• Remove the slide
containing plant cells.
• Dispose of the onion skin,
as directed by your
teacher.
• Clean the slide and cover
slip with lens paper.
4 Switch to low power and
remove the slide. Put on
rubber gloves and goggles.
• Place a drop of iodine
stain at one edge of the
cover slip. Touch the
opposite edge of the
cover slip with paper
towel to draw the stain
under the slip.
• View the cells under
medium and high power.
(a) What effect did the
iodine have on the cells?
(b)Draw a group of four
cells. Label structures
you see.
(c)Estimate the size of
one cell.
6 Place the prepared slide
of human epithelial cells
on the stage.
• Using the coarseadjustment knob, locate
and focus on a group of
the cells.
• Switch to medium power
and focus using the fineadjustment knob.
(a)Is the arrangement of
plant and animal cells
different? Explain.
(b)Draw a group of four
cells and label the cell
structures you can see.
Analysis
7 Analyze your results by
answering the following.
(a)In what ways do the onion
skin cells differ from the
human skin cells?
(b)Why is it a good idea to
stain cells?
(c)Predict the function of
the onion cells that you
observed under the
microscope. What
prominent cell structures
would justify your
prediction?
(d)Explain why the cells of
an onion bulb do not
appear to have any
chloroplasts. (Don’t all
plant cells have
chloroplasts?)
(e)A student viewing onion
cells sees just large, dark
circles. What might have
caused the dark circles?
Did anyone in your class
experience this difficulty?
(c)Estimate the size of
each cell.
Cells, Tissues, Organs, and Systems
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