Core Practical: Investigate biological specimens using microscopes,…

The idea

This Core Practical asks you to use a light microscope safely and record what you see. Prepare a slide, focus on low power first, then increase magnification, adjusting the coarse then fine focus. Measure the observed image and the actual specimen to calculate magnification using magnification = image size ÷ actual size, keeping both in the same unit. Rearrange to find actual size or image size as needed. Produce a labelled scientific drawing: use a sharp pencil, draw clear continuous lines, keep proportions accurate, add straight label lines that do not cross, and state the magnification used. Do not shade or draw what you cannot see. Record observations honestly and link structure to function in your labels.

What earns the marks

• Uses the microscope correctly: prepares the slide, focuses on low power first, then increases magnification.
• Calculates magnification as image size divided by actual size, with both measurements in the same unit.
• Rearranges the magnification equation to find actual size or image size.
• Produces a labelled scientific drawing with clear continuous lines, accurate proportions and straight uncrossed label lines.
• States the magnification used and labels visible structures accurately.

Common mistakes and how to put them right

• Mixing units, such as image size in mm and actual size in µm, before dividing.

  Put it right by converting both to the same unit.

• Shading or adding detail not visible through the eyepiece.

  Put it right by drawing only observed structures with clear lines.

• Starting on high power and losing focus.

  Put it right by focusing on low power first, then increasing magnification.

Exam tips

• Write the magnification equation before substituting values so rearrangement is clear.
• Convert both measurements to the same unit, often micrometres, before calculating.
• Check drawings use a sharp pencil, continuous lines and straight label lines that do not cross.