Using a Microscope
Use a light microscope correctly to prepare, focus, and examine biological specimens, including making accurate labelled drawings at an appropriate magnification
What a learner can do afterwards
- Sets up a light microscope safely and correctly (course focus then fine focus)
- Prepares a wet mount slide with a biological specimen (e.g. onion skin)
- Calculates the magnification of an image (magnification = image size ÷ actual size)
- Draws an accurate labelled diagram of observed cells with a scale
The lesson
A light microscope uses two lenses to make a tiny specimen look much bigger: the eyepiece you look through, and the objective lens close to the slide. Always start on the lowest-power objective. Turn the coarse focus knob first to bring the image roughly into view, then switch to the fine focus knob to sharpen it.
To look at onion cells, peel a very thin layer of skin from the inside of an onion scale. Lay it flat on a slide, add a drop of water, then lower a coverslip onto it at an angle from one edge, so no air bubbles get trapped underneath. A drop of iodine stain makes the cell walls easier to see.
Magnification tells you how much bigger the image looks compared to the real object: magnification = image size ÷ actual size. If a cell measures 6 mm across in your drawing but is really 0.06 mm wide, the magnification is 6 ÷ 0.06 = 100.
When you draw what you see, draw only what's really there. Use a sharp pencil, label the parts with straight ruled lines, and add a scale line so anyone reading your drawing knows the real size.
Focus on low power first, mount your slide carefully, then work out and record the magnification of what you draw.
Watch it
Where it sits
Learn first
This opens up
Nothing builds on it yet.
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.