Mitosis in Onion Root Tips

Mitosis has always been one of my favorite biology topics to teach and create lessons for. I can still hear a mitosis song in my head that I heard over and over for years from a mitosis video I used to show my students. It was a fun video- definitely engaging- it was funny and made the students laugh while at the same time explained the stages of mitosis very well. But even still, it is one thing to talk about cell division in notes, read about it, or see a video on it, and quite another thing to see the stages in person using a specimen under a light microscope. And students love to use microscopes, and the only class they are going to have the opportunity to use one is in their biology class.

Microscope labs are a great way for students to see the mitosis stages. Onion root tips are commonly used in mitosis labs in grades 8-12 because the tip of the onion contains meristematic tissue, an active region of cell division for plants. This tissue is rich in actively dividing cells. This means in any given slide sample, you will see cells in different phases of the cell cycle: interphase, prophase, metaphase, and telophase. It is really pretty neat to see.

Speaking of neat to see, before the lab, or sometime during your mitosis unit, show a time lapse video of cells undergoing mitosis to form an embryo.

There is a detailed process for preparing fresh onion roots in class using 70% Isopropyl or ethyl alcohol, acetocarmine, hydrochloric acid, a water bath, Spirit lamp, and a fixative solution. I have never done this lab from scratch myself. It does have some safety hazards handling some of the material in it and takes some time to prep the onion root tips for this lab. Also, many things can go wrong in the prepping portion of this lab, which can cause the root cells to not be seen at all, or it may not be clear when students go to view it under a microscope. It might take several tries and before students can get a good view of the onion root tip cells. This is why I do not recommend preparing the root tips as a class for the 9th grade biology class and below. Just my opinion. Now maybe for an AP biology class or college...

But if you want students to engage in the from scratch steps, you can do this too. You would want to place the root tip part of a scallion in water for a few days to grow the tips. Once they are long, you would snip them for use in the lab. It definitely would be more exciting for students to do it from scratch, so if this something you want to try in your classes, and think your students can manage a task like this, then go for it! Find a lab for this and try it out. Just be sure to review the safety rules and procedures well before doing the lab with them. You could also try and do the prepping yourself and get the onion root tips ready for your students ahead of time.

I just do not recommend anything in my blogs that I have not tried myself, and I have not done this lab from scratch. With middle school or high schoolers, I prefer using pre-prepared onion root slides that you can buy from science lab supply companies online. This will you save time and get your students right into the part where they observe the onion root cells in their various stages on the cell cycle. These slides are not expensive and can last you years if handled with care. With these pre-prepared slides, students will see cells in interphase, prophase, metaphase, anaphase, and telophase.

If you want a mitosis worksheet to go with this lab, I have a Mitosis Onion Root Stages Worksheet in my store. It is two pages and comes with answer key.

Here are some other premade microscope slides I recommend you buy to show your students:

• Red blood cells

• White blood cells

• Platelets

• Human skin with hair follicle

• Cardiac muscle

• Skeletal muscle

• Smooth muscle

• Neurons

• Human cheek cells

• Bacteria (Bacillus, coccus, spirillum)

• Euglena

• Diatoms

• Amoeba proteus

*I like Carolina Biological Science Supplies for slides, but you can buy these from other science supply companies as well. There are many science supply companies selling pre-made slides.