How to Observe Onion Cells under a Microscope

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The onion cell lab is a classic in biology classrooms and it’s easy for Homeschool Microscope Lessons. Observing Onion Cells under a Microscope is one of my most popular posts of all time and it’s a great introduction to the microscope using easily accessible materials. Enjoy an up close view of plant cells.

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If you are studying life science or biology this year,

one of the easiest labs in cell biology is observing onion cells under a microscope.

I thought it would be helpful to share how I help students to see an example of a plant cell.

Today’s objective:  Observing Onion Cells under a Microscope

The goals for this lesson are to:

  • Make a wet mount slide.
  • Observe an onion cell under the microscope.
  • Record our observations.

Materials Needed for Observing Onion Cells

You will need to purchase some science materials for this lab exercise.

The nice thing about purchasing the appropriate supplies is that you’ll have them on hand the next time you want to use your microscope.

I like to buy supplies from Amazon and Home Science Tools depending on the availability and price.

  • Set of Microscope Slides– You can purchase a blank set of slides to use for your microscope work.
  • Cover Slips– This is placed over the specimen to keep it in one spot on the slide.
  • Pipette– Eye dropper. I like to use disposable droppers because I don’t have to worry about cleaning them.
  • Microscopic Life Kit– has all the microscope supplies for this lab and many more.
  • Iodine– to stain the cells so it can be seen under the microscope. Not all cells can be stained with iodine, but onion cells take it up nicely so that there is contrast under the microscope.
  • Onion– Peeled to one layer. If it’s any thicker, you won’t be able to see through it under the microscope.
  • Microscope– A simple light microscope will be sufficient. We use this 1000x LED Microscope. I love how the stage moves, so we don’t have to move the object. This is great for people who lose track of what their looking at!
  • Lab Sheet– We made our own for recording some simple observations. You can subscribe below for two different styles you can use for drawing what you see and comparing it at different magnifications.

Staining Onion Cells

middle schooler applying a stain to a microscope slide

Since onion peels are translucent,

you’ll need to stain the onion cells before you observe them under the microscope.

There are different types of stains depending on what type of cell you are going to look at.

  • Iodine– dark stain that colors starches in cells. In an onion cell, it will make the cell wall more visible. It provides some contrast for viewing under a microscope.
  • Methylene Blue– a blue stain that will color blood, bacteria, acidic or protein rich cell structures like nucleus, ribosomes, and endoplasmic reticulum.
  • Eosin Y– a pink or red stain that colors blood, plants, and alkaline animal cell structures like the cytoplasm.
onion cell stained with Methylene blue at 400x

The Microscopic Life Kit from Home Science Tools contains both Eosin Y and Methylene Blue for staining many types of cells.

Preparing the Onion Cells for the Microscope Slide

Science Quest Observing Onion Cells
Iodine is a great choice because it’s a household product, but more sophisticated stains will allow you to see more structures in the onion cell.

The procedure is fairly simple.

You just need to be careful as you work to get a good peel of an onion.

You want a single layer of cells or you won’t see much under the microscope.

In order to see the cells well, the light needs to pass through easily.

  • Peel Your Onion– You want one layer of it and it should be super thin.
  • Place the Onion Peel onto the Slide– You’ll want to smooth out any wrinkles with forceps or the end of your pipette
  • Put One Drop or Two of Iodine– onto the top of the onion cell. If you are using Methylene blue, you’ll need to apply the stain next to the cover slip after it is down. Go light because too much will mean you can’t see the cell well.
  • Drop the Cover Slip– over the onion cells by placing one end of the cover slip into the iodine and dropping the other side down. This helps to prevent bubbles.
  • Check for Bubbles– if you see one, you can try and remove it by lightly tapping with the bulb end of the pipette or placing a tissue on the liquid at the edge of the cover slip close to the bubble.
  • Observe under the Microscope– Place the slide on the stage of the microscope and observe under all three levels of magnification.
Science Quest Observing Onion Cells

Observing & Recording Your Observations

To prepare for recording your observations, have your students create a data sheet. Having your students make their own data sheet helps them to organize information. I usually give the following directions.

  • We go over what we will be recording and make a list.
  • Remind them to include the objectives or the goal of the lab along with the materials.
  • Think of the best way to record the information we need to write down. Remember that even if it’s not the way you would do it, all that is important is that everything is written down and that it makes sense to your student. You will see growth in this area as they get older.
Science Quest Observing Onion Cells
Our old Intel Play Microscope even showed onion cells.

In this case, we want to record as much as we can about what we see. For example:

  • The goal of the lab exercise
  • List the materials we will use.
  • Make a place to draw what you see under each level of magnification.
  • Label the places with 10x, 60x, and 200x
  • Leave a space for writing a conclusion describing what we able to see.

Teacher Hint: You will not be able to see the individual organelles with a standard light microscope. The most noticeable item will be the cell wall. In general, you will see a group of neat rectangles with an outer layer (the cell wall). The higher the magnification, the more defined the cell wall will become and the field of view will be smaller so you will see less rectangles.

Science Quest Observing Onion Cells

Free Microscope Observations Lab Printable

More Microscope Lessons

The Beginner’s Guide to Using the Microscope– This post contains a full video tutorial on using a light microscope.

10 Reasons a Digital Microscope is an Amazing Science Tool– an updated post on choosing and using a digital microscope in your homeschool. They are a pleasing alternative to expensive microscopes.

3 Easy Steps to Observing Pond Life under the Microscope– How to collect

The Beginner’s Guide to Microscopic Life in a Pond– Need help identifying what you observed from your pond sample? Or do you need to know what to look for at all? This is the place!

How to Capture & View Snowflakes under a Microscope– The title says it all, but this is a fun and addicting activity. Once you see one, you’ll be after more!

The Snake Project– A year long 8th grade life science project during which Rebecca (now in her first year of college at an Ivy League school) studied biology through the lens of snakes. It was a fabulous year of in depth study which she can now draw on as she studies high school biology.

Entomology The Science of Insects– We have two entomologists in our house who collect and pin specimens regularly. This is a series of posts which shares equipment, collection, pinning, and displaying.

It’s my hope that you will be able to take this science lesson and apply it in your homeschool easily.

Microscopic Marvels Online Course

An affordable, year long course devoted to the study of microscopy through hands on observation, research, and scientific journaling. Just $67 for a high school, college prep microscope course that is friendly to out of the box and neurodivergent teens.

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