Microscope Techniques and Biological Drawings

Looking closely at biological specimens

Many biological structures are too small to examine clearly with the unaided eye. A light microscope passes light through a thin specimen and uses lenses to produce a larger image. You might observe cells in a prepared slide of plant or animal tissue, then record the structures you can actually see. This is the microscopy work in OCR's Practical Activity Group 1: the aim is not just to look, but to make an observation that someone else can understand from your labelled scientific drawing.

Using the microscope

Place a prepared slide on the microscope stage, with the specimen over the opening where light passes through. Start with the lowest-power objective lens. Looking through the eyepiece, adjust the light and use the focusing control until the specimen comes into view. Starting at low power makes it easier to locate the specimen and see a wider area. Centre the part you want to examine before changing to a higher-power objective for more detail; refocus carefully afterwards. Handle glass slides and lenses with care, and follow your teacher's safety instructions.

You may instead make a slide from a thin sample of tissue. Place the specimen on the glass slide; a suitable stain can make some cell structures easier to distinguish. Lower a cover slip gently over it, rather than dropping it flat, and blot away excess stain. The specimen needs to be thin enough for light to pass through. Prepared slides are also suitable for observing and drawing cells: making every slide yourself is not the point of this task.

Turning an observation into a drawing

A scientific line drawing is a record of evidence, not a decorative picture. Choose a clear view and draw the shapes and arrangement you observe at a useful size. Use a sharp pencil and smooth, continuous outlines; avoid sketchy repeated strokes and shading. Add a title identifying the specimen. Label only structures you can distinguish, using straight label lines that point precisely to them, and state the magnification used. If a structure is not visible in your specimen, do not add it simply because you know that it can occur in that kind of cell.

The microscope image and the drawing serve different purposes. Changing the objective lens can reveal different detail, while the drawing selects and communicates the visible features. Together, careful focusing and accurate labelling allow another person to understand what you observed rather than what you expected to see.