Microscopy - How to use a microscope - GCSE Science Required Practical

Microscope Setup and Usage

Introduction to Microscopes

• The session focuses on the practical use of microscopes, a crucial tool in biological experiments.

• The first task involves examining onion skin tissue under the microscope as part of a required practical.

Microscope Components

• Key components include a light source, mirror, stage (platform for samples), and various objective lenses (4x, 10x, 40x magnification).

• The eyepiece lens provides an additional 10x magnification; combined with objective lenses, total magnifications range from 40x to 400x.

Preparing the Specimen

• To prepare an onion skin sample: collect a glass slide while avoiding fingerprints and peel off a thin layer of onion skin.

• Place the thin layer on the slide, add iodine drops to stain starch in cells for better visibility, and cover with a slip while minimizing air bubbles.

Focusing Techniques

Troubleshooting Focus Issues

• If unable to focus on the specimen: start with the lowest magnification lens (4x), adjust stage height close to lens.

• Use coarse focus dials for initial adjustments; fine focus dials allow for precise focusing once cells are visible.

Adjusting Magnification

• After achieving focus at low magnification, switch to higher objectives (10x or 40x), ensuring no contact between lens and slide during adjustment.

• Always look from the side when adjusting high magnifications to prevent damage; make small adjustments for clarity.

Measuring Cell Size

Estimating Cell Dimensions

• To measure cell size: use middle magnification (10x), align view across several whole cells within field of view.

• Measure width of field using a transparent ruler placed under microscope; convert measurements from millimeters to micrometers for accuracy.

Calculating Average Cell Size

• Divide total field width in micrometers by number of observed cells to estimate average cell size; example shows each cell is approximately 500 microns wide.