Like any other multicellular living thing, leaf structure is made up of layers of cells. Viewing the leaf under the microscope shows different types
of cells that serve various functions. Using a microscope, it's possible to
view and identify these cells and how they are arranged (epidermal cells,
spongy cells etc). To do this a compound microscope is required given that it
allows for higher magnification.
While a compound microscope is ideal for
viewing the internal leaf structure, a stereo microscope would be the
ideal tool for observing the external structure of a leaf (vein, lamina etc).
External Leaf Structure
To view the external leaf structure, the
following will be required:
Stoma refers to the minute pores that can be
found on the epidermis of a leaf. These pores vary in size and allow for the
movement of water and gases in and out of the intercellular spaces. The
following is the procedure for viewing (as well as estimating stomatal
frequency) stoma on the surface of a cell.
Clear nail polish
A compound microscope
Microscope glass slide
Microscope cover slip
Apply clear nail polish on
to the surface of the leaf (flattened leaf)
Allow the nail polish about
four hours to dry
Using a pair of tweezers,
peel off a film (thin skin) from the surface of the leaf
Gently place the film onto
a microscope slide and cover with a cover slip
Start with low power and
increase to 100x (frequency of stoma can be counted at 100x)
Record your observations
While the compound microscope would be more
effective for viewing the frequency of the stoma, a stereo dissecting
microscope can also be used for this purpose. For instance, by viewing a
Zebrina plant leaf (older leaf) it's possible to view the stomata as green
patches with a purple background.
When viewing the surface of the leaf under the
stereo microscope, students will be able to clearly see hair-like structures
(trichome) on the leaf surface that serve a number of functions ranging from
trapping insects to trapping water/moisture. Students will also observe the
intricate leaf veins (vascular bundles) running across the surface of the leaf.
With some leaves (such as the maple leaf), it's
possible to isolate the vascular bundles (vein structures) for viewing under
A hot plate
a cooking pot
A small brush
Simmer the leaf for about
an hour and a half
Once the leaf starts
feeling slimy, remove from the pot and place on a plate/Petri dish
Add a small amount of water
and gently remove the soft part using a small brush from both sides of the leaf
Place the leaf vein
(vascular bundles) between two hard surfaces (such as a book) to prevent from twisting
View the leaf vein under
the microscope (stereo microscope or under low power on compound microscope)
When viewing the cells of a leaf, this should be
done using a compound microscope. The procedure used allows for
the stomata to be seen.
A compound microscope
Glass slides and cover
Having obtained a leaf, carefully fold it and
using a pair of tweezers, peel off the lower surface of the leaf
(epidermal membranous transparent layer)
Place the peel into a watch glass that contains
Remove the epidermal skin from the watch glass
and transfer to another watch glass with safranin for about 30 seconds (few
drops of safranin solution)
Move the epidermal skin from the safranin
solution and place it in the glass with water once again to remove excess stain
Place the epidermal skin onto a clean, dry
glass slide and add a few drops of glycerine
Cover the epidermal skin on the slide with a
After removing excess glycerine with a blotting
paper, place the slide on the microscope for observations
When viewed under the microscope, it's possible
to see the epidermal cells that tend to be irregular. In addition to the
epidermal cells, one will also see the leaf spores (stomata) in between the
epidermal cells. Typically, the stomata are bean shaped and will appear denser
(darker) under the microscope.
Under high magnification, students can differentiate between
closed and open stomata. The bean-shaped structures are
referred to as guard cells and contain a nucleus and chloroplasts.
Leaf Cross Section Under the Microscope
Whereas the transparent thin epidermal skin of
the leaf allows the student to observe the stomata and other epidermal cells,
it would be important to prepare a cross section of a leaf to observe the
arrange of cells inside the leaf structure.
A sharp razor
A compound microscope
Glass slides and cover
Take one leaf and roll it
Using a razor, cut through
the roll to obtain a very thin slice (to obtain a very thin, almost transparent
Place the slice onto a microscope
glass slide and add a one drop of water
Under high magnification, students will be able
to view the internal structure of the leaf. This includes the upper and lower epidermal
cells (flattened cells) with the mesophyll layer in between.
Here, the mesophyll
section of the leaf contains two different type of cells including the palisade
mesophyll (elongated cells) and the spongy mesophyll (spherical or ovoid). This
part of the leaf structure also has air spaces.
Using the stereo and compound microscope,
students can view different parts and structures of a leaf. These include both
the external and internal structures. With a wide range of leafs available,
students can obtain different types of leaves (thick and long leaves etc) and
compare the appearance of such structures as the stomata, shape and arrangement
This can be an important lesson to help students understand the
differences in the arrangement and size of the cells and stomata between
different types of leaves and consequently learn the significance between these
differences. For instance, students may notice larger stomata in thick leaves
that allows for the leaves to release more water compared to smaller stomata in
thin leaves that serve to preserve water.
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