Observing Cork Cells Under The Microscope

Whether it’s from a human, animal, or plant, most cells look highly similar to one another. Because the cells of all living things share a variety of common intrinsic structures, the resemblance between, say, a human red blood cell and that from a dinosaur is often uncanny.

These similar cellular structures and components include the cell membrane, mitochondria, cytoplasm, nucleus, and nucleolus, which are the basic parts of any cell.

In this article, we’ll talk about cork cells- what they are, how they look like under a microscope, who first observed cork cells, and so on.

Contents show

What are cork cells?

First of all, what are cork cells, exactly? To answer this question, it is important to talk about where cork cells come from.

Cork, also referred to as cork cambium, is a tissue (more specifically, a lateral meristematic tissue) that exists as a part of a vascular plant’s epidermis or outer layer. It is present in woody and herbaceous dicots, as well as in a few gymnosperms. The cork cambium of a plant typically consists of incompletely differentiated cells where the plant grows from.

The cork that we will tackle here is a composition of dead tissues that come from the outer bark of a tree called the cork oak, which is a type of evergreen oak tree.

Parts of the cork cambium

In some cases, cork cambium is also called perikambium, bark cambium, or more notably, phellogen. Basically, the part of the plant that is responsible for the periderm’s growth is called the phellogen. The cork, or phellem, are the cells that grow outwards, while cells that develop inwards are referred to as phelloderm.

Simply put,

The phelloderm is the innermost part of the cork cambium, and is made up of living parenchyma cells that can grow inwards or outwards,
The phellogen, which is the cork cambium itself, is the assortment of meristem tissues giving rise to the periderm, and
The phellem, or the cork, is a protective tissue that is located externally, is filled with air, and becomes dead at maturity

Cork cambium growth and development

How the cork cambium of a plant grows and develops depends entirely on the plant species, as well as the age of the plant, its growing environment and other influencing conditions. It is possible to tell the health, condition, and other properties of the cork cambium by looking at the bark’s varying surfaces, which can be smooth, scaly, fissured, flaking off, or tessellated.

What is the function of cork cells?

The cork of a plant is responsible for the plant’s secondary growth. This works as the cork replaces the epidermis in the roots and stems of the plant. Another function of the cork cambium is to produce a protective layer that covers the outermost part of the plant.

Commercial use

While cork cells serve an important role in a plant’s growth, development, health, and overall life, these cork cells and tissues eventually die as they mature. However, their usefulness does not stop there. For one thing, homeowners and landscapers often use bark as mulch.

Moreover, commercial cork, which comes from the cork oak tree’s bark, has many different uses, since it has a high strength to weight ratio, as well as being a cost ablative material. Some of the many applications of cork include:

Wine bottle stoppers, coasters, bulletin boards, protective hot pads for cooking pans
Lid sealing, insulation, flooring, engine gasket
Handles for tennis rackets, fishing rods, and the like
Wind tunnel applications (as aerodynamic prototypes)
Vehicle payload fairings in satellite launches
Compression joints for solid rocket motor nozzles that are thrust-vectored

Who first looked at cork cells under a microscope?

In the early stages of the 19th century, or around 300 years ago, cork cells were first observed by Robert Hooke, an English scientist, using a primitive microscope. This moment was also the first recorded use of a microscope.

During his observations, Robert Hooke noticed small box-like structures in the cork, which he later on realized were the cork’s cells. In a sense, looking at cork cells disproved Hooke’s first hypothesis that only plants contain cells. Another interesting thing is that what he actually saw were just the cell walls since the cells themselves have already dried out.

In any case, this eventually helped him formulate the cell theory, which essentially identifies cells as the smallest unit of life. He also deduced that cells make up all living things and that cells come in various shapes and sizes, each with different functions. This understanding of a cell’s basic nature has propelled biology and microscopy to a new era.

What microscope do you need to observe cork cells?

Observing cork cells only necessitate low magnification levels, along with plenty of light. Even at low magnifications of, say, 10x to 40x, you will already see plenty of detail inside the cell. Hence, you can use just about any kind of light microscope to do the job. In this procedure, we will be using a conventional compound microscope.

How to observe cork cells under a microscope

Here is a simple methodology you can follow in order to see cork cells under a microscope. We will be using a container of cork dust or cork shavings, and look at their cells using a compound light microscope.

Requirements

You will need a small cork sample from the bark of your chosen plant. You can also take several samples from different plants (or different parts of a single plant) and compare the appearance and characteristics of their cork cells.

Also, grab a single-edge razor blade, making sure to be careful with the sharp edge. Other items you will need are a microscope slide and a cover slip. And of course, don’t forget your compound microscope.

Preparation

A useful tip before we begin: instead of using intact cork, go for the bits and shavings, or even the cork dust lining the bottom of your container. This will help you better see the individual cork cells, and in clearer detail at that.

Method 1

To start, prepare a wet mount by placing a tiny water droplet on the center of a clean microscope slide. Using a wet mount will keep the cork sample in place instead of sliding or flying off of the slide.
Then, dip your finger inside the cork container to pick up some dust or shavings.
Place the cork dust on the microscope slide with a drop of water, then add another water droplet on top of the cork sample.
Cover the prepared slide with a cover slip.

Method 2

Alternatively, slice thin cork slices, making sure that ample light can pass through the slice, allowing you to see the cell layout and the individual cells.
If you choose this method, take a few sheets of paper, or a thick paper towel, and place the cork sample on it.
Get a sharp razor blade and slice off one thin section. Do it slowly and carefully to ensure that you get a thin, even, and clean surface for optimal viewing later on.
Place the sample on a wet mount, similar to the process above.

Mount the prepared slide on the microscope stage plate, and secure it with the stage clips. Align the viewing area along the sample’s thinnest edge to be able to get the clearest possible view of the cork cells.

Procedure

To view the cork cells, start with low power objectives. This will offer several benefits: You’ll get a similar view as to what Robert Hooke observed with his primitive microscope that only made use of low power lenses, and it will be easier to adjust the focus, brightness, and contrast of the image, since low magnification lenses, are not as sensitive to minute adjustments.

Set the microscope to the lowest magnification by clicking the 10x objective into position. Do this by turning the compound microscope’s revolving turret until the right objective is set in place.
Look at the specimen through the eyepiece of the microscope, and using one hand, adjust the focus knob in small increments until the resulting image comes into focus with as much cork cells’ definition and detail as possible.
Adjust the amount of light from the illumination system and manipulate the condenser slightly so that the specimen can be illuminated with the optimum intensity and brightness level. You can also add another light source at a slight angle coming from the top of the microscope.
Center the microscope slide in the microscope’s viewing field by moving the glass slide around the stage plate. Again, looking at the thinnest edge of the sample will offer the best view of the cork cells.
After aligning the view, readjust the illumination, condenser, and focus of the image.

Take notes of what you can see using the 10x objective lens, then move on to higher (or lower) magnifications and observe the differences in terms of the sizes of the cell parts and the amount of detail you can see.

You can also zoom in and out while using one objective lens to experiment with different views, or point the objective lens towards various viewing planes so you can better observe the layout of the cork sample.

Finally, once you are finished observing the cork cells, carefully set the objective back to the lowest magnification, lower the microscope stage, and remove the microscope slide.

Observations

When looking at cork cells under a microscope, you will likely see clusters of dead cells, which are cork cells that have died at maturity. As such, the most notable feature you will be able to observe are the remaining cell walls, which are made of suberin, a waxy substance that’s highly impermeable to gases and water.

Depending on what type and species of plant you took the cork sample from, you may also notice traces of fatty acids, lignin, or tannin in the cells. More commonly, however, dead cork cells are simply empty, air-filled cells in which the cell walls vary in thickness.

What do cork cells look like?

At low magnifications of around 10x, you will already be able to distinguish individual cork cells. These cells will likely appear to be closely packed together and are arranged radially in neat rows. Unless you are looking at young cork cells, which will display all the basic cell parts, cork cells will simply look hollow.

What structure do you see inside cork cells?

Meanwhile, at much higher magnification levels starting at around 40x, more detail of the individual cells start to become visible, including the separation between the individual cork cells, which is a result of the lenticels.

The lenticels are pore-like core cell structures in the cork cell arising from the phellogen/ cork cambium. These structures are what facilitates the exchange or flow of gases between the plant stem and its external environment.

Summary

Observing cork cells under a microscope is a fun and easy activity that will help you gain insight on various cell parts, functions, and characteristics. There are also several ways you can go about viewing cork cells, each with slightly different results.

Regardless of which method you choose to go with, remember that the best way to see the most detail is to look at the edge of the cork sample rather than the center since this is where the most light passes through. Moreover, manage your expectations especially when viewing old cork, since the cells here have already dried out, so you will likely only see the cell wall.

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