1.1.8 The Microscope

The Microscope

Introduction

The discovery of the microscope revolutionized Biology. Before its invention, scientists could only study what they could see with the naked eye — the external features of plants and animals. But the microscope opened a new world of discovery by allowing biologists to see structures invisible to the human eye, such as cells, tissues, microorganisms, and organelles.

The microscope is therefore one of the most important tools in Biology. It helps scientists, teachers, and students to magnify tiny objects and observe their details clearly. Through microscopes, we know that all living things are made up of cells — a fact that forms the basis of modern Biology.

In this section, you will learn about the types of microscopes, their parts and functions, how to use and care for a microscope, and its importance in biological studies.

Meaning of a Microscope

A microscope is an optical instrument that enlarges the image of small objects so that they can be seen clearly. The word comes from two Greek words:

Micros = small

Skopein = to view or look at

Therefore, microscope means “an instrument for viewing small objects.”

The microscope works by bending light rays through lenses, which magnify the specimen. Depending on its design and power, a microscope may use light or electrons to form images.

History of the Microscope

The development of the microscope dates back to the late 16th and early 17th centuries.

Around 1590, Dutch lens makers Hans and Zacharias Janssen built the first compound microscope.

In 1665, Robert Hooke used a microscope to observe cork cells and coined the term cell.

In the late 1600s, Anton van Leeuwenhoek, a Dutch scientist, built simple microscopes and became the first person to observe microorganisms such as bacteria and protozoa.

Over time, microscope technology improved — from simple microscopes to compound microscopes and later electron microscopes, which can magnify objects millions of times.

Types of Microscopes

Simple Microscope

A simple microscope has only one lens. It works like a magnifying glass and can magnify objects up to about ×20.

Examples: Hand lens or magnifying glass.

Uses:

Observing small plant or insect parts in the field.

Preliminary examination of specimens before using a compound microscope.

Advantages:

Portable and easy to use.

Inexpensive.

No electricity required.

Disadvantages:

Limited magnification.

Cannot view very small structures such as cells.

Compound Microscope

A compound microscope has two or more lenses — the objective and the eyepiece — that work together to produce greater magnification (up to ×1,000 or more).

It is the most common type used in schools and laboratories.

Features:

Uses light from a mirror or lamp.

Produces high-resolution images.

Suitable for viewing cells, tissues, and microorganisms.

Electron Microscope

An electron microscope uses a beam of electrons instead of light to produce an image. It can magnify objects up to 1,000,000 times.

Types of electron microscopes:

1. Transmission Electron Microscope (TEM) – for viewing internal structures of cells.

2. Scanning Electron Microscope (SEM) – for viewing the surface of specimens in 3D.

Advantages:

Very high magnification and resolution.

Can reveal structures at molecular levels.

Disadvantages:

Very expensive.

Requires trained personnel.

Cannot view living specimens.

In schools, learners mainly use simple and compound microscopes.

4. Parts of a Compound Microscope and Their Functions

The compound microscope has two main parts:

Optical parts (involved in magnification), and

Mechanical parts (for support and adjustment).

A. Optical Parts

Part Description Function

Eyepiece (ocular lens) Lens at the top of the microscope Magnifies image formed by the objective lens (usually ×10)

Objective lenses Found on the revolving nosepiece (usually ×4, ×10, ×40) Provides main magnification of the specimen

Condenser Lens below the stage Focuses light on the specimen

Mirror or light source Located below the stage Reflects or provides light for viewing

Diaphragm Adjustable disc under the stage Controls amount of light passing through the specimen

B. Mechanical Parts

Part Description Function

Base Heavy bottom part Supports the microscope and gives stability

Arm Curved back part Connects base to top; used for carrying the microscope

Stage Flat platform Holds the specimen slide with clips

Stage clips Small metal arms Secure the slide on the stage

Coarse adjustment knob Large knob Brings image roughly into focus

Fine adjustment knob Small knob Sharpens image for clarity

Body tube Long metal tube Connects eyepiece and objective lenses

Revolving nosepiece Rotating disk holding objectives Allows change of magnification easily

Each part works together to provide a clear, magnified view of microscopic structures.

5. How a Microscope Works

The microscope functions by gathering and focusing light rays from the specimen to produce a magnified image.

Steps in Image Formation:

1. Light from the mirror or lamp passes through the condenser and diaphragm.

2. The light illuminates the specimen on the slide.

3. The objective lens magnifies the image.

4. The eyepiece lens further magnifies the image and directs it to the eye.

Total Magnification = Magnification of Objective Lens × Magnification of Eyepiece

Example:

If the eyepiece is ×10 and the objective lens is ×40,

then Total Magnification = 10 × 40 = 400×.

6. Steps in Using a Compound Microscope

1. Place the microscope on a flat table near good light.

2. Adjust the mirror so that light passes through the condenser.

3. Select the low-power objective lens (×4 or ×10).

4. Place the specimen slide on the stage and secure with clips.

5. Look through the eyepiece and adjust the coarse focus slowly until the image appears.

6. Use the fine adjustment knob for a clearer view.

7. Adjust the diaphragm to regulate light intensity.

8. Change to high power (×40) if needed for finer details.

9. Record your observation — draw, label, and note magnification used.

10. After use, lower the stage, remove the slide, clean lenses, and cover the microscope.

7. Preparation of Microscope Slides

A microscope slide is a small piece of glass used to hold a specimen for observation.

Temporary (Wet Mount) Slide

Used for fresh specimens like leaf peels or cheek cells.

Procedure:

1. Place a drop of water on the slide.

2. Put the specimen in the water drop.

3. Lower a cover slip gently to avoid air bubbles.

4. Remove excess water using tissue paper.

5. View under the microscope.

Permanent Slide

Used for specimens fixed and stained permanently for repeated study (prepared in laboratories).

Staining Biological Specimens

Most biological specimens are colorless, making them difficult to see clearly.

A stain is a colored chemical that adds contrast to structures in cells.

Common Stains Used:

Stain Use

Iodine solution Stains starch in plant cells

Methylene blue Stains nuclei in animal cells

Eosin Highlights cytoplasm

Safranin Used for plant tissues like stems

Staining helps identify specific parts of cells such as nuclei, chloroplasts, and vacuoles.

Drawing Biological Diagrams from Microscopic Observations

Biological drawing is a key skill in laboratory work. It allows learners to record accurate representations of what they observe.

Guidelines:

1. Use a sharp HB pencil.

2. Draw large, clear outlines — avoid shading.

3. Label using a ruler and horizontal lines.

4. Write title and magnification below the diagram.

5. Include only visible structures.

6. Use neat, scientific labeling (e.g., Nucleus, Cell wall).

Example:

“Drawing of an Onion Epidermal Cell (×400)”

Care and Maintenance of a Microscope

Proper care ensures long life and accuracy of the microscope.

Handling:

Always carry the microscope with both hands — one on the arm, one under the base.

Avoid touching the lenses with fingers.

Never tilt the microscope while a slide is in place.

Cleaning:

Use only lens paper or soft cloth to clean lenses.

Wipe dust from the body with a dry cloth.

Clean stage and slides after use.

Storage:

Lower the stage and remove the slide.

Rotate the low-power objective into position.

Cover with a dust cover.

Store in a dry cabinet.

Protection:

Avoid exposing to moisture.

Do not attempt to repair parts yourself.

Report any damage immediately to the teacher or technician.

Advantages and Limitations of Microscopes

Advantages

Enables observation of minute structures.

Helps understand cell structure and function.

Supports research in medicine, genetics, and microbiology.

Provides visual evidence for biological theories.

Useful for identifying diseases through blood and tissue samples.

Limitations

Requires training and care to use.

Cannot view large or opaque specimens.

Limited field of view.

Electron microscopes are expensive and complex.

Applications of the Microscope

Microscopes are widely used in different fields of science and health:

Field Application

Education Teaching students about cells and microorganisms

Medicine Diagnosing diseases from blood, urine, or tissue samples

Agriculture Studying plant diseases, pests, and crop tissues

Environmental science Observing microorganisms in water and soil

Research Developing vaccines, studying genetics, and biochemistry

Forensics Analyzing hair, fibers, and tissues in crime investigations

The microscope is therefore indispensable in both learning and applied biological sciences.

Troubleshooting Common Microscope Problems

Problem Possible Cause Solution

Image too dark Light source blocked or diaphragm closed Adjust mirror or open diaphragm

Image blurred Slide not in focus or lens dirty Clean lenses and refocus

Spots in field of view Dust on lenses Clean gently with lens paper

No image visible Objective not clicked into position Adjust objective lens

Slide moves Stage clips loose Secure slide properly

Learning to identify and fix such issues helps students become confident microscope users.

Importance of the Microscope in Biology

1. Foundation of Cell Theory: Led to discovery that all living things are made of cells.

2. Advances in Medicine: Helped identify bacteria, viruses, and body tissues.

3. Genetic Research: Enabled scientists to study chromosomes and DNA.

4. Improved Agriculture: Allowed identification of plant pathogens and pests.

5. Understanding Ecology: Helped study microorganisms in ecosystems.

6. Innovation and Technology: Microscopy has led to advances in biotechnology and nanotechnology.

Without microscopes, modern Biology would not exist in its present form.

Summary

A microscope is an instrument used to magnify small objects.

The compound microscope is the main type used in schools.

It consists of optical parts (lenses, light) and mechanical parts (support and adjustment).

Microscopes must be handled with care and kept clean.

They are essential for studying cells, microorganisms, and biological materials.