Mastering Microscopes for GCSE Biology

Microscopes are an essential tool used in Biology to explore microscopic details within cells, tissues and microorganisms. Understanding how to effectively set up and use microscopes as well as making accurate interpretations of the images, is crucial for mastering GCSE Biology.

This article will provide an overview of the origins of microscopy and highlight the advancements in technology over time. I will share my top tips for using microscopes in the laboratory, equipping you with the knowledge and skills to handle microscopes like a pro.

The evolution of microscopes

The first light microscopes were developed in the 17th century by several scientists including Hans and Zacharias Janssen and Anton van Leeuwenhoek. However, it was Robert Hook who used the devices to show the existence of cells.

Over time, the design of the light microscope has evolved providing increased magnification and resolution to enhance the detail of the specimen being studied. In the 20th century, the first electron microscopes were developed. Using electron beams, these microscopes allowed scientists to study specimens with a much higher resolution and magnification than was possible for a light microscope.

Types of microscopes

There are different types of microscopes with characteristics which make them more suitable for a certain purpose.

Light microscopes

Light microscopes, sometimes called optical microscopes, are the most commonly used in GCSE Biology. They use visible light to illuminate samples and lenses to magnify the image. They are ideal for viewing live specimens and stained slides of cells and tissues in a school laboratory as they are easy to set up, small in size and more affordable for department budgets than electron microscopes. The maximum useful magnification of optical microscopes is about ×1500 which makes them less useful for technical microscopy used in scientific research.

Electron microscopes

Electron microscopes come in two main types: transmission electron microscopes (TEM) and scanning electron microscopes (SEM), although the GCSE course does not go into detail about specific types. Electron microscopes use electrons to form the image, this gives a much higher resolution and magnification than a light microscope and so allow the study of much smaller subcellular structures e.g. the mitochondria, the nucleus or the cell membrane. This makes electron microscopes much more suitable for scientific research as the maximum useful magnification of electron microscopes is about ×1,500,000. However, use of electron microscopes requires training as specimen production is more complicated. Additionally, they are much more expensive and larger so they cannot be moved once installed.

The resolving power of an electron microscope is much greater than that of the light microscope, as structures much smaller than the wavelength of light will interfere with a beam of electrons

Components of a microscope

In my experience, I have found that setting up an optical microscope is much simpler if you can identify some key components:

• The ojective lenses are the primary magnifying lenses on a microscope which allow us to observe different levels of detail within the specimen. Typically, these are found in various magnifications e.g. 4x, 10x, 40x.

• The eyepiece lens is the lens at the top of the microscope which you will look through to observe the specimen. Usually, this magnification is 10x and so it multiples the magnification of the objective lens by this amount e.g. 10 (eyepiece lens) x 4 (objective lens) = 40x overall magnification.

• The course and fine-focusing mechanisms adjust the distance between the objective lens and the sample. The course focus is used to bring the sample into view and the fine focus is used to sharpen the image.

• The light source must be positioned to direct light through the specimen to make it visible. Some microscopes have a mirror that can be adjusted to reflect light from an external source, I find these a bit fiddly to set up.

The components of an optical microscope

Using microscopes

Preparing a slide

The slide must be prepared with care to ensure the clarity of the image seen through the microscope.

1. A thin layer of sample tissue should be placed on a glass slide

2. Place a drop of stain over the sample (if needed)

3. Cover the sample with a coverslip

4. Tap the coverslip gently to remove any air bubbles

5. Place the slide on the stage, securing it with the clips

Adjust the focus

You should always start with the low power objective lens to initially view your specimen. For each objective lens, you will need to:

1. adjust the coarse focus first until the specimen appears on the screen. At this point, it may well be blurry.

2. adjust the fine focus to bring the specimen clearly into view

Taking measurements

Once you have a clear image of the specimen visible through your microscope, you can use a calibrated eyepiece graticule to take measurements.

A graticule is a small disc which is added to the eyepiece of the microscope and then calibrated using a stage micrometer with engravings of a known size to work out the size of the graticule engravings under the chosen magnification.

In the image below, the eyepiece graticule is shown over some onion cells on the left. The image on the right shows how the eyepiece graticule is aligned with a stage micrometer to calculate the size of each division on the graticule.

Calculating magnification

You may be asked to complete calculations based on the sizes of specimens and the magnification used to observe them.

A common mistake in students I have worked with is to forget to standardise the units.It is important to make sure that you convert all the numbers that you are working with into the same unit.

The equation that we use is:

Magnification = image size ÷ actual size

This equation can be rearranged to find each component:

• Actual size = image size ÷ magnification

• Image size = actual size × magnification

I have found that many students prefer using the equation triangle to work out the correct arrangement

Challenges and limitations of microscopy

The resolution of a microscope limits the detail of the specimen that can be viewed. This is particularly evident with light microscopes which have a much lower resolution than electron microscopes. If you want to see specific structures in the specimen being studied, it is important to ensure that the resolution will allow you to do this effectively.

Issues that arise during sample preparation can limit the value of the specimen that is being observed. It is important to follow procedures carefully to maximise the value of the observations made.

Artifacts and distortions can occur during preparation. The observer must be aware of these so as not to confuse them for cellular components.

Applications of microscopes in Biology

Studying cells and tissues

Light microscopes allow the study of live cells and tissues such as those seen in the leaf tissue shown below. As light microscopes allow live tissues to be observed, the functions of the cells in the tissue can also be studied.

Electron microscopes allow a more in-depth view of cellular structures, although the specimens are no longer living once they have been prepared.

Investigating microorganisms

Microorganisms cannot be seen with the naked eye and so microscopes are required to develop our understanding. Many microorganisms are pathogenic and are therefore of great interest to scientists who strive to understand more about diseases to direct future progress in fighting and eradicating transmissible diseases

• Bacteria are commonly studied, even in the school laboratory you may find that you are given the opportunity to work with bacteria such as e-coli. However, due to the pathogenic nature of many bacteria, there are strict rules surrounding their use in schools.

• Viral particles are also observed using microscopes, however, due to the fact that all viruses are pathogenic, research is significantly regulated and study environments are carefully controlled.

Exploring biological processes

Processes such as cell division, protein synthesis, muscle contraction and transport into and out of cells has all be developed with the use of microscopes.

The future of microscopy in Biology

Developments in imaging technology

Advances in imaging technology, such as super-resolution microscopy is increasing the level of detail that can be observed giving much better insight into biological structures and processes.

Combining microscopy with other techniques

Complex microscopy can be combined with the use of computers and bioinformatics to enhance our understanding of complex biological systems and enable more comprehensive research.

Image by: https://www.freepik.com/free-photo/laboratory-supplies-medical-work_32501175.htm#query=computer%20microscope&position=1&from_view=keyword&track=ais_user&uuid=fad830e6-0ca7-4293-8d9b-869d907b72f8 

Magnify your Biology Knowledge ahead of your exams

Microscopes are vital tools in biology, enabling the exploration of cells, tissues, and microorganisms at a microscopic level. The intricacies of the details that can be studied depends on the type of microscope used and other possible technologies which can be used in conjunction with the microscope. 

Optical microscopes are the simplest microscopes available and so their use is commonplace in the GCSES Biology classroom, mastering their use is crucial for success in GCSE Biology.

In GCSE Biology, the use of the optical, or light, microscope is common place and so it is important to be able to identify the key structures on the microscope in order to examine each specimen accurately. Slide preparation is another key skill which will impact the quality of the observations made through your microscope.

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