Leaf Structure Under the Microscope

** Preparation, Requirements and Observations

Introduction

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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 

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To view the external leaf structure, the following will be required:

 

• A stereo microscope
• A leaf (try finding a leaf that is not dry or decaying)

 

Observation 1 (leaf surface)

 

Procedure

 

• Place a small leaf on the microscope (stereomicroscope)

• Start with low power and increase gradually and record your observation

** See more info on Chloroplasts and Chromoplasts.

Observation 2 (stomata)

 

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.

 

Requirements

 

• Clear nail polish
• A leaf
• A compound microscope
• Tweezers
• Microscope glass slide
• Microscope cover slip

 

Procedure

 

• 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.

Leaf Structure Observations

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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 the microscope. 

 

Requirements

 

• Maple leaf
• A hot plate
• a cooking pot
• A small brush

 

Procedure

 

• 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)

 

Compound Microscopy - Bright Field

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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.

Requirements

 

• A compound microscope
• Tweezers 
  
• A needle
• Glass slides and cover slips
• Safranin
• Glycerine 
• Distilled water 
• Watch glass

Procedure

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 distilled water

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 cover slip

After removing excess glycerine with a blotting paper, place the slide on the microscope for observations

Observations

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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

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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.

Requirements

• A sharp razor
• A leaf
• Distilled water 
• A compound microscope
• Glass slides and cover slips

 

Procedure

• 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 slice)
• Place the slice onto a microscope glass slide and add a one drop of water
• Place on the microscope and observe

Observation

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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.

Conclusion

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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 of cells.

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.

Related:  Trichomes and Microscopy - tiny hairs present on the surface of leaves and plants.

More Fun with your Microscope

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Cheek Cells 

Onion Cells

Pond Water Microorganisms and a closer look at Diatoms

Yogurt

Spider Web

Yeast Cells

Mold

Sugar Crystals

Check out Petri Dish with Agar - Preparation, Requirements and Procedure

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Related:  Plant Biology overview, Mesophyll Cells, Meristem Cells. Plastids, Chloroplasts, Guard Cells, Photosynthesis, Epidermal Cells, Chlorophyll, Micropropagation

Bacteria that cause disease in plants: Pseudomonas Syringae

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