make temporary preparations of cellular material suitable for viewing with a light microscope

The Microscope in Cell Studies

Objective

To make temporary (wet) preparations of cellular material that are suitable for observation with a light microscope.

Why Temporary Preparations?

• Preserve the natural colour and morphology of living cells.
• Allow observation of movement, growth and reactions to stimuli.
• Require simple equipment and can be prepared quickly in the laboratory.

Key Equipment

• Compound light microscope (objective lenses 4×, 10×, 40×, 100× oil immersion).
• Glass microscope slides and cover slips.
• Dissecting needles, tweezers, scalpel or razor blade.
• Staining solutions (e.g., iodine, methylene blue, carmine).
• Distilled water and dropper.
• Mounting medium (optional for longer observation).

General Procedure for a Wet Mount

1. Clean the slide and cover slip. Rinse with distilled water and dry with lint‑free tissue.
2. Obtain the specimen. Use a dissecting needle or scalpel to place a small amount of the material (e.g., onion epidermis, cheek cells, pond water) on the centre of the slide.
3. Add a drop of liquid. Place a drop of distilled water, saline, or appropriate staining solution onto the specimen.
4. Place the cover slip. Hold the cover slip at a 45° angle and gently lower it to avoid air bubbles.
5. Remove excess liquid. If necessary, blot the edges with tissue to prevent the cover slip from moving.
6. Observe. Start with the lowest power objective and centre the specimen, then increase magnification as required.

Staining Techniques for Temporary Preparations

Staining enhances contrast by adding colour to otherwise transparent structures.

• Iodine solution (1% I₂KI): Used for starch grains; dip the slide for 10–15 seconds.
• Methylene blue (0.1%): Stains nuclei and bacterial cells; apply a drop directly onto the specimen.
• Carmine (0.5%): Highlights plant cell walls and nuclei; briefly immerse the slide.

Calculating Total Magnification

The total magnification (\$M\$) of a light microscope is the product of the ocular (eyepiece) magnification (\$O\$) and the objective magnification (\$E\$):

\$M = O \times E\$

For example, using a 10× eyepiece with a 40× objective gives \$M = 10 \times 40 = 400\times\$.

Common Pitfalls and How to Avoid Them

• Air bubbles: Lower the cover slip gradually and avoid dropping it directly onto the liquid.
• Specimen movement: Use a small amount of specimen and a thin cover slip; seal edges with petroleum jelly if needed.
• Over‑staining: Rinse briefly with water after staining to remove excess dye.
• Damage to the slide: Do not use excessive force when spreading the specimen; a gentle smear is sufficient.

Summary Table