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Microscopes

A microscope is a device used to view things that are small, such as cells and sub-cellular structures. The microscope creates an enlarged image of whatever is placed in it, making it possible to study things that would otherwise be too small to see.

There are several different types of microscopes, each with their own advantages and disadvantages.

Light microscopes

The first type of microscope to be invented was the light microscope. A light microscope works by shining light through the sample. This light then passes through two lenses, which magnify the image, before passing into the eyes of the person using the microscope.

Photograph of a light microscope.

A light microscope. (Photo by dustin day from FreeImages)

Image captured through a light microscope. It shows a large number of leaf cells, each one with a cell wall and a nucleus, which have both been stained green. The wall of each cell has an elongated geometrical shape, with about 5 to 7 straight edges. The cells are arranged roughly in rows.

Cells from a leaf of a garlic plant, viewed through a light microscope. (Photo by Krzysztof (Kriss) Szkurlatowski from FreeImages)

In order to observe cells using a light microscope, the cells first need to be placed on a thin piece of glass called a slide.

Photograph of a microscope slide being held up in a person's hand. The slide has a purple coloured sample of biological tissue on it.

A microscope slide with a sample on it. (Photo: Stained microscope slide by Waughd on Wikimedia Commons - licensed under CC BY-SA 4.0)

The slide is then placed on the microscope and light shines through it, allowing a magnified image of the cells to be seen through the microscope's eyepiece.

Magnification

The magnification of an image is the number of times larger the objects in the image are than the actual objects.

For example, if you are looking at a cell through a microscope and the width of the cell in the image is two hundred times greater than the width of the actual cell, then you would say that the image has a magnification of 200X (pronouned '200 times').

The magnification of a light microscope can be changed by using different lenses.

The maximum amount of magnification possible is different for different types of microscopes.

Diagram illustrating the principle of magnification. On the left is a small cell. Then there is an arrow pointing to the right. The arrow is labelled '10X'. The arrow points to an image of the same cell but ten times wider.

Magnification means that the object in the image is bigger than the actual object. In this case, the image has a magnification of 10X, meaning that the cell in the image is 10 times wider than the actual cell.

Resolution

Resolution, also known as resolving power, is the ability to distinguish between close together points in an image.

The more resolving power a microscope has, the closer together two objects can be and still be seen as two distinct objects.

If the microscope does not have enough resolving power to distinguish between two close together objects, then they will appear blurred together into one object.

Diagram demonstrating resolution. On the left there are two circular objects that are blurred so that they look like they are touching. This is labelled, 'Low resolving power. Objects appear as one'. On the right the same two objects are shown buy this time their edges and sharp and it can be seen that there is a gap between them. This labelled, 'High resolving power. Objects can be seen as separate'.

Resolution is the ability of a microscope to distinguish between objects that are close together.

Image showing the difference between high resolution and low resolution. On the left is a high resolution electron microscope image of part of a cell's nucleus. A lot of detail can be seen. On the right is the same image at a much lower resolution. It is much blurrier and much less detail can be seen. The images are labelled "High Resolution" and "Low Resolution".

The same electron microscope image of part of a cell's nucleus shown at high resolution and low resolution (the nucleus is the round structure that takes up most of the image - not just the dark circle in the bottom left corner). The nucleus is surrounded by a double membrane - in the high resolution image this can be seen as two separate lines, whereas in the low resolution image it blurs into one line.

Flashcards

Flashcards help you memorise information quickly. Copy each question onto its own flashcard and then write the answer on the other side. Testing yourself on these regularly will enable you to learn much more quickly than just reading and making notes.

1/4

What is a microscope?

2/4

What was the first type of microscope to be invented?

3/4

What is magnification?

4/4

What is resolution?

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