Microscopy and measuring cells — Edexcel GCSE Combined Science
Light and electron microscopes, estimation, units from milli to pico, and the core practical on using a microscope.
Revision notes
4 short notes, in the order of the specification. Each one in short:
An electron microscope uses a beam of electrons and has a much higher magnification and resolution than a light microscope. Resolution is how well two points close together can be seen as separate points. Because of this, sub-cellular structures such as ribosomes and the inside of mitochondria can be seen in detail, which has increased understanding of their functions.
An estimation is an approximate answer, usually found by rounding numbers to one significant figure. In biology, estimations are used to check that a calculated answer is sensible, to find a value when an exact count is impossible or too slow, and to compare sizes quickly, such as roughly how many times bigger one cell is than another.
Milli, micro, nano and pico are units each 1000 times smaller than the one before: 1 mm = 1000 µm, 1 µm = 1000 nm and 1 nm = 1000 pm. To convert to a smaller unit multiply by 1000, and to a larger unit divide by 1000. Standard form uses negative powers of ten for small numbers.
Core practical: using a microscope
PracticalIn this core practical, a light microscope is used to observe cells such as onion epidermis. A thin layer is placed in a drop of water or iodine on a slide, a coverslip is lowered at an angle, and the cells are focused on low power first. Magnification = size of image ÷ size of real object.
Exam questions
6 exam-style questions (18 marks), each with its mark scheme.
Answer the questionsFlashcards
11 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of key concepts in biology on one page, so you can see where this subtopic fits.
Open the mind mapPractical sheet
Method, variables, risks and a results table, with questions to answer.
Print it
Free PDFs to print or save.
Quick check questions
Why can electron microscopes show more detail than light microscopes?
Show answer
They have a higher magnification and higher resolution.
How many nanometres are there in 1 µm?
Show answer
1000 nm.
Convert 0.05 mm into µm.
Show answer
50 µm (0.05 × 1000).
State the equation linking magnification, image size and real size.
Show answer
magnification = size of image ÷ size of real object.
Why is a coverslip lowered at an angle?
Show answer
To avoid trapping air bubbles.
Frequently asked questions
How do you calculate magnification in biology?
Magnification is calculated using magnification = size of image ÷ size of real object. Both sizes must be in the same unit, so convert first, for example from mm to µm by multiplying by 1000. To find the real size, rearrange to real size = image size ÷ magnification. Total microscope magnification is eyepiece × objective.
What is the difference between magnification and resolution?
Magnification is how many times bigger the image is than the real object, while resolution is how well a microscope can show two points close together as separate points. Electron microscopes have a much higher magnification and resolution than light microscopes, so they show fine detail such as ribosomes and the inside of mitochondria.
How many micrometres are in a millimetre?
There are 1000 micrometres (µm) in 1 millimetre. Each unit in the sequence millimetre, micrometre, nanometre and picometre is 1000 times smaller than the one before. To convert to a smaller unit, multiply by 1000; to convert to a larger unit, divide by 1000. For example, 0.2 mm is 200 µm.
How do you make a scientific drawing of cells?
Use a sharp pencil to draw clear, continuous lines with no shading or colouring. Draw large and only draw what you can see. Label with straight lines drawn with a ruler that touch the structure they name and do not cross. Give the drawing a title and write the magnification.
Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026