Key points
- All living organisms are made up of cells.
- Cells are the smallest part of a living organism and are around 0.01 mm - 0.03 mm long.
- To look at a cell close up a microscope needs to be used.
Game - onion cells
Play an Atomic Labs activity to look at onion cells under a microscope.
You can also play the full game
Video - Observing cells with a microscope
Find out how to observe cells under a microscope
Let's take a look at how to observe cells under a microscope.
No prizes for guessing the first thing you'll need: a microscope. But don't worry if you don't have one of your own. Ask your school if they have one you can use. Then you'll need an onion. That's where you'll get your plant cells. Some food colouring - blue or green works best. A cotton bud. And a mouth. It's probably best to use your own.
So let's begin by looking at some plant cells. Cut a small chunk from your onion. Be careful with knives. Ask an adult if you need help. Peel a thin layer off that chunk and put it on your slide. This is what's called the epidermis. Using a drop of food colouring, stain the layer so you can see the cells. Pop a cover slip on the slide and then put the slide onto the microscope. Take a look! Check out that strong cell wall structure. It's solid so that it keeps a plant's shape and structure.
But this experiment isn't over. You can look at some animal cells too.
Grab a fresh slide and pop a drop of your food colouring on there. Take your cotton bud and rub the inside of your cheek. Told you you'd need a mouth. Transfer the cheek cells to the slide by rubbing the swab all over it. Drop the cover slip on the slide and stick it on the microscope. Go find those animal cells! Unlike the plant cells, animal cells are soft and fleshy. Animals don't need cells to keep their structure. That's what skeletons are for.
And there you have it. Now you have the skills to look at really tiny things.
Step by step
Image caption, Click to see a step-by-step slideshow.
Image caption, YOU WILL NEED: An onion, a slide and cover slip, a cotton bud, some food colouring, a plate to put the cotton bud on and of course a microscope!
Image caption, STEP 1 - Carefully cut an onion in half (or ask an adult). Peel a thin layer of onion (the epidermis) off the cut onion.
Image caption, STEP 2 - Place the layer of onion epidermis carefully on the glass slide, and cover with a cover slip.
Image caption, STEP 3 - Stain the layer of onion with food colouring.
Image caption, STEP 4 - View your onion cells.
Image caption, STEP 5 - Rub the tip of a clean cotton bud against the side of your cheek.
Image caption, STEP 6 - Stain the slide by rubbing it with a cotton bud dipped in food colouring.
Image caption, STEP 7 - Rub the cotton tip (with your cheek cells on it) against the food colouring.
Image caption, STEP 8 - Enjoy looking at your cheek cells!
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Try the experiment online
Try out this experiment in Atomic Labs. Go to the Biology lab and try the Investigating onion cells experiment.
Atomic Labs game. gameAtomic Labs game
Try out practical experiments in this KS3 science game

How to use a microscope
Move the stage (the flat ledge the slide sits on) down to its lowest position.
Place the glass slide onto the stage. Be careful pushing it under the clips that the cover slide doesn't move or crack.
Select the lowest power objective lens.
Turn the coarse focus knob slowly until you are able to see the cells.
Turn the fine focus knob slowly until the cells are in focus and you can see them clearly.
Repeat steps 1-5 using the higher power magnification to see the cells in more detail.
Calculating magnification
To see an object, the eye piece lens and the objective lens magnification are multiplied together to give the total magnification.
Total magnification = eye piece lens magnification × objective lens magnification
For example: 10 × 20 = 200
Magnification = 200
Teaching resources
Are you a biology teacher looking for more resources? This series of short films examines the human body through spectacular graphics based on the latest science and stories of remarkable people around the world.
BBC Teach has thousands of free, curriculum-linked resources to help deliver lessons - all arranged by subject and age group.
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