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Biology Paper 1 / Cell biology
Lesson 1.3 · AQA Combined Science

Using a microscope

01 · Find the parts

A closer look at cells

A light microscope uses light and lenses to produce a magnified image. Tap a part to see its job.

02 · Prepare a slide

Thin sample. Clear view.

For an onion slide, use a thin piece of the inner epidermis (skin). A thick piece blocks too much light.

1. Add the specimen

Put a drop of water on a clean slide. Use forceps to lay the thin onion skin flat in it.

2. Add a stain

Add a drop of iodine solution. The stain increases contrast, making cell structures easier to see.

3. Lower the coverslip

Lower it gently at an angle with a mounted needle. This helps avoid trapping air bubbles.

4. Place it on the stage

Secure the slide with the clips. Centre the specimen over the hole so light passes through it.

Side-view diagrams are enlarged. Follow your teacher’s instructions; wear eye protection when using iodine and handle glass carefully.

03 · Get a sharp image

Low power first

  1. Select the lowest-power objective. It gives a wider view, so cells are easier to find.
  2. Looking from the side, bring the objective close to the slide without touching it.
  3. Look through the eyepiece. Use coarse focus to move the lens and slide further apart until an image appears.
  4. Use fine focus to sharpen it. Centre the cells, then select a higher-power objective if needed. Refocus using fine focus.

Bring the cells into focus

A focus model: it changes sharpness, not the size of the cells.

04 · Record what you see

A biological drawing

Clear lines and labels

Use a sharp pencil and single, unbroken outlines. Draw large, keep proportions sensible and use straight label lines. Do not shade.

Plant and animal cells

Observe both in this required practical. Label only structures you can see. Include a magnification scale with your record; we will practise scales in lesson 1.4.

These are schematic examples, not actual microscope observations.

05 · Bigger or more detailed?

Magnification and resolution

Magnification: how many times larger the image is than the object.

Resolution: the ability to distinguish two close points as separate.

Electron microscopes have higher magnification and higher resolution than light microscopes. They reveal smaller structures in greater detail, helping scientists understand cells.

Making a blurry image bigger does not reveal extra detail.

Remember the practical

Thin specimen → stain → coverslip → low power → focus.

Draw what you see and label it clearly.