2.5 Microscope—Simple, Compound, & Electron

The microscope is an essential tool for biology students to observe very small objects that are invisible to the naked eye. There are two main types of microscopes:

1. Light Microscope: Uses light to magnify objects.

2. Electron Microscope: Uses electrons for magnification, allowing much higher resolution.

2.5.1 Simple Microscope

A simple microscope is made up of a flat stage with a vertical pillar. It has:

• Stage: Where the slide is placed.

• Mirror: Reflects light through the stage.

• Lens: A lens is used to focus on the object on the slide.

The object is observed by adjusting the focus with a screw to bring it into view.

2.5.2 Compound Microscope

A compound microscope is more complex and includes several parts for magnification and focusing:

• Stand: Vertical pillar supporting the microscope.

• Arm: Curved part above the stand.

• Base: Platform beneath the stand.

• Stage: Attached to the arm and holds the slide.

• Body Tube: Tubular part holding the eye piece and objective lenses.

• Eye Piece: Lenses located at the upper end of the body tube (usually 10x-20x magnification).

• Objective Lenses: Mounted on a rotating nosepiece. Common lenses include:

• Low Power Objective (10x-12x)

• High Power Objective (40x-45x)

• Oil Immersion Objective (100x)

• Coarse Adjustment Knob: Used to bring the object into rough focus.

• Fine Adjustment Knob: Used for fine-tuning the focus.

• Diaphragm and Condenser: Control light intensity and focus light onto the object.

• Illuminator: Light source, either a mirror or light bulb, to illuminate the object.

Using the Compound Microscope:

1. Ensure the microscope is in a well-lit area.

2. Use the mirror to adjust natural light, or use an artificial light source.

3. Place the slide on the stage and use the clips to hold it in place.

4. Start with the lowest power objective lens and use the coarse adjustment knob to bring the object into focus.

5. Use the fine adjustment knob for clearer focus.

6. To view objects at higher magnification, switch to higher power lenses by rotating the nosepiece.

Staining:

Staining is a technique used to enhance the contrast of cells or tissues in a microscope. It involves applying dyes that selectively stain certain parts of the cell, making it easier to see structures like organelles or tissue components. These dyes are known as stains.

2.5.3 Electron Microscope

• Function: Uses electron waves instead of light to provide much higher magnification and resolution.

• Why It’s Needed: Light microscopes cannot magnify objects smaller than 200 nm (e.g., organelles inside cells). Electron microscopes solve this issue as the wavelength of electrons is much shorter, enabling a clearer view of smaller objects.

• Components:

• Electron Waves: Used for magnification.

• Electromagnets: Used instead of glass lenses to focus electron waves.

• Image Display: The magnified image cannot be viewed directly; it is processed and shown on a computer monitor.

Electron microscopes allow scientists to observe details such as the structure of organelles within a cell, which would be impossible with light microscopes.