The Microscope in Cell Studies

This section details the techniques required to prepare temporary slides of cellular material for observation under a light microscope. Accurate preparation is crucial for clear and detailed observation of cellular structures.

Objectives

• To make temporary preparations of cellular material suitable for viewing with a light microscope.
• To understand the principles of making wet mount slides.
• To identify common staining techniques used in cell biology.

Materials Required

The following materials are typically required for preparing temporary cell slides:

• Microscope slides
• Coverslips
• Dropper bottle
• Pipettes
• Scalpel or scalpel blade
• Forceps
• Water bath or distilled water
• Stains (e.g., methylene blue, iodine)
• Paper towels
• Specimen (e.g., onion epidermis, cheek cells, pond water)

Making a Wet Mount Slide

A wet mount slide is a simple preparation method where a thin layer of specimen is placed in water on a slide, covered with a coverslip.

Procedure

1. Place a drop of water on the microscope slide.
2. Using a scalpel or forceps, carefully place the specimen in the water.
3. Gently lower a coverslip onto the water, avoiding air bubbles.
4. Slowly bring the coverslip down to prevent air bubbles from being trapped.

Considerations

Ensure the coverslip is placed at a 45-degree angle to avoid trapping air. Avoid over-saturating the slide with water.

Staining Techniques

Staining is often used to enhance the visibility of cellular structures. Different stains highlight different components of the cell.

Methylene Blue Staining

Methylene blue is a basic dye that stains negatively charged cellular components, such as DNA and proteins. It is commonly used to visualize nuclei.

Procedure:

1. Prepare a wet mount slide as described above.
2. Add a drop of methylene blue solution to the slide.
3. Gently lower a coverslip onto the water, avoiding air bubbles.

Iodine Staining

Iodine is used to stain starch granules, making them visible in plant cells. It also stains other cellular components.

Procedure:

1. Prepare a wet mount slide as described above.
2. Add a drop of iodine solution to the slide.
3. Gently lower a coverslip onto the water, avoiding air bubbles.

Preparing a Thin Section (e.g., Onion Epidermis)

For thicker specimens like onion epidermis, a thin section is required to allow light to pass through.

Procedure

1. Carefully peel a thin layer of onion epidermis from the inner surface of an onion.
2. Place the epidermis on a microscope slide.
3. Gently place a coverslip over the epidermis, avoiding air bubbles.
4. Optionally, stain the section with methylene blue or iodine.

Microscope Use

After preparing the slide, it can be viewed under a light microscope. Follow these steps:

1. Place the slide on the microscope stage and secure it with clips.
2. Start with the lowest power objective lens (e.g., 4x) to locate the specimen.
3. Slowly increase the magnification to higher power objectives (e.g., 10x, 40x) for detailed observation.
4. Adjust the focus using the coarse and fine focus knobs.

Equipment	Purpose
Microscope Slides	To hold the specimen for viewing.
Coverslips	To protect the specimen and provide a flat surface for viewing.
Dropper Bottle	To dispense water and stains.
Pipettes	To accurately transfer liquids.
Scalpel/Forceps	To handle and position the specimen.
Water Bath	To maintain a constant temperature and prevent specimen drying.