Animal and plant cells: Required practical activity 1: use a light microscope to observe, draw and label a selection of plant and animal cells. A magnification scale must be included.

The idea

This practical develops skill in using a light microscope safely and correctly to view cells. You prepare a slide, for example onion epidermis for a plant cell and human cheek cells for an animal cell, then focus using the coarse and fine adjustment knobs, starting on the lowest power objective. You observe the cells, then produce clear biological drawings with sharp pencil lines, no shading, and labels with straight lines that touch the structure. Every drawing must include a magnification scale, such as a line labelled with its actual length and the calculated magnification, so the size of the specimen is communicated. Magnification is calculated as image size divided by actual size, with units converted consistently. Accurate observation, correct technique and clear, labelled drawings with a scale are all assessed.

What earns the marks

• Selects the correct lens, usually the lowest power objective first, and focuses using the coarse adjustment knob before refining with the fine adjustment knob.
• Prepares a suitable slide, for example a thin onion epidermis or cheek cell sample, adding a stain such as iodine or methylene blue where appropriate and lowering the coverslip carefully to avoid air bubbles.
• Draws cells using clear, continuous pencil lines without shading, keeping the drawing large enough to show internal structures such as the nucleus, cytoplasm, cell membrane and, in plant cells, the cell wall and vacuole.
• Labels structures with straight, uncrossed lines that touch the named part, and includes a title stating the specimen and the magnification scale.
• Calculates magnification correctly using magnification = image size ÷ actual size, converting units such as mm to µm before dividing, and records the scale on the drawing.
• Observes and records differences between the plant and animal cells seen, such as the presence of a cell wall and large vacuole in plant cells and their absence in animal cells.

Common mistakes and how to put them right

• Using the high-power objective immediately.

  Put it right by starting with the lowest power objective, focusing with the coarse knob, then moving to higher power and using only the fine knob.

• Shading the drawing or using sketchy, broken lines.

  Put it right by using clear, continuous pencil lines and leaving the cell interior unshaded, as shading hides detail and is not accepted in biological drawings.

• Forgetting the magnification scale or leaving labels as floating words.

  Put it right by adding a labelled scale line with its actual length and magnification, and by drawing straight label lines that touch the structure being named.

Exam tips

• Practise calculating magnification from measured image size and actual size, converting units carefully, for example 1 mm = 1000 µm, before dividing.
• When describing the method, write the steps in order: prepare the slide, place it on the stage, select the lowest power objective, focus with the coarse knob, then refine with the fine knob.
• In drawing questions, plan the layout so labels fit around the drawing without crossing lines, and always state the specimen and magnification.