microscope

Have you wondered how scientists observe and study cells yet they are so small? They do this with the help of a microscope.

What is a microscope?

A microscope is an instrument that enlarges the image of an object. Biologists make use of microscopes to study microscopic objects. These objects are too small to see with a naked eye. These objects can be cells, parts of cells, or small organisms.

Microscopes serve the purpose of magnifying, and showing the details of an image.

The major types of microscopes are light microscope, and electron microscope. A light microscope is one that uses light to magnify an object. In this microscope, light is passed through lenses in order to produce a magnified or enlarged image of the specimen being studied.

An electron microscope uses a beam of electrons, instead of light to magnify a specimen.

EARLY MICROSCOPES

Scientists that began, and made initial progress in the idea of magnification of specimens include:

• Robert Hooke. Robert Hooke is a scientist who discovered cells. He used a microscope to observe a slice of cork. He observed spaces in the cork which he named cells. The name cell comes from small rooms where monks lived. After more research on the cell using the microscope, he described the cell as the smallest unit of life. He used microscopes made of two and three lenses but the images he produced were not very clear.

• Anton van Leeuwenhoek. He was a Dutch merchant who discovered how to grind lenses and make a microscope with only one lens. This made it possible for his microscopes to produce more enlarged images, and clearer than Hooke’s microscopes. He is referred to as the father of microscopy, after having built more than 500 different microscopes. He was the first person to discover microorganisms using a microscope. He observed a drop of water from a pond and referred to the organisms as “tiny animalcules”. He also made observations and studied bacteria.

PARTS OF A LIGHT MICROSCOPE

• Body tube. This is the part that keeps apart the two sets of lenses.
• Rotating nose piece. This is the part that allows you to change the objective lenses, from one to another.
• Objective lens. This is normally the second set of lenses. A compound microscope usually has 3 sets of lenses with magnification (x4, x10, and x40).
• Stage clips. These serve the purpose of holding the specimen in place.
• Diaphragm. This part moderates the amount of light that comes from the light source and reaches the slide.
• Light source. A light microscope uses light for magnification. A light source produces the light needed to pass through a specimen to produce a magnified image of the specimen.
• Ocular lens. This is the first lens from where an observer observes the specimen under study.
• Arm. This is the part that provides support to a microscope and is also used for holding a microscope.
• Stage. This is the location where an observer puts the slide and specimen for observation.
• Coarse adjustment knob. This is the part that moves the stage up and down.
• Fine adjustment knob.

In compound light microscopes, light is made to pass through a specimen placed on a slide, and uses 2 lenses to form a magnified image.

A compound microscope is capable of two things, Magnification, and resolution.

Magnification refers to the measure of how much an image of an object has been enlarged. Total magnification is gotten by multiplying ocular lens with objective lens used. The ocular lens normally has a magnification of x10 but it may vary. Therefore, the magnification of a compound light microscope under different objective lens is as following:

4x objective lens = (10x) x (4x) = magnification of 40 times

10x objective lens = (10x) x (10x) = magnification of 100 times

40x objective lens = (10x) x (40x) = magnification of 400 times

Resolution refers to the measure of clarity of an image, how clear the details of an image are.

Resolution is a major limitation of light microscopes. This is because, the larger the magnification, the lesser the resolution of an image. A magnification beyond 200x makes the image to look blurry in a light microscope but a greater magnification and resolution can be achieved using an electron microscope.

THE ELECTRON MICROSCOPE

The following are characteristics of an electron microscope:

• It uses a beam of electrons to produce a bigger image of the specimen. It does not use light like the light microscope.
• The specimen and the electron beam must be in a vacuum chamber. This is to prevent beam electrons from bouncing off gas molecules in the air.
• An electron microscope is limited in its usage as it cannot be used to observe living organisms. This is because living organisms cannot survive in a vacuum.
• The electron microscope is more powerful than the light microscope.

RULES FOR USING THE COMPOUND LIGHT MICROSCOPE

• Always carry the microscope using one hand to hold the arm, and the other giving support under the base.
• Plug in and turn on the power source.
• Dry the stage and place your slide. Hold the slide in place by arranging the stage clips.
• Always start using the low power objective lens 4x. Focus this lens using the coarse adjustment knob. Carefully change to the medium power objective lens and focus using the coarse adjustment knob. Carefully change from medium to high power objective lens 40x. Be careful not to touch the slide. When using the 40 x (high power objective lens), do not use the coarse adjustment knob.
• Make your observations.
• Using the coarse adjustment knob, lower the stage.
• Switch the objective lens to low power 4x.
• Turn off the light source and unplug the cord.

SUMMARY

You’ve learned:

• What is a microscope?
• Types of microscopes.
• Characteristics of microscopes.
• How to use a microscope.