In eukaryotes there is a nucleus, so a more complex process called mitosis is needed with cell division. Mitosis is divided into four parts, or phases:
Phase 1 – Prophase: In this phase the nuclear membrane begins to break down and the DNA forms structures called chromosomes.
Phase 2 – Metaphase: In this phase the chromosomes line up along the center of the parent cell
Phase 3 – Anaphase: In this phase, the chromosomes break apart, with a complete set of DNA going to each side of the cell
Phase 4 – Telophase: In this phase, a new nuclear membrane forms around each of the sets of DNA
The four stages of mitosis (the cell at the top has not started mitosis) lead to two daughter cells.
A little after telophase, the cytoplasm splits and a new cell membrane forms. Once again, two daughter cells have formed. Take a look at this animation for a good overview of mitosis and see if you can identify all the phases.
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Cells continue to divide until a protein tells them to stop. As they divide, they become different and specialized, eventually making the tissues and organs found in the many different living things we see every day.
Download Student Worksheet & Exercises
Mitosis is part of the cell cycle, a larger process that living organisms use to repair damage, grow, or just maintain condition. In this experiment, we’re going to figure out the time it takes for a cell to go through each of the four mitosis states.
Grab your science journal and here’s what you do:
Materials:
- Compound microscope with slides and coverslip
- Onion (the root tip, not the onion itself) – you can grow your own if you can’t find any at the store (see image at above left). Place the bottom of an onion in a glass of water for a couple of days and you’ll see the roots grow to the size you need (about 2 cm long).
- Science journal
First, set up your microscope.
Next, prepare an onion sample. Take it from the root tip called the meristematic zone (use the picture on the right), just above the root cap at the very end of the tip.
Use the staining technique we show in our Microscope Lab. Cut the sample lengthwise before placing it on the slide.
If you want to stop the cell division process while you watch the slide, you’ll need to prepare a heat fix mount instead (make sure you don’t boil the liquid when you use the candle or you’ll ruin your slide). You can add a drop or two of stain after the heat fix and blot the excess with a paper towel. Add a drop of water and a coverslip and you’re ready to look!
Try different powers of magnification to find the four different stages of mitosis. Count the number of cells found at each stage of mitosis and figure out the percentage. (Total up the number of cells and use this number to divide each count by. Don’t forget to multiply by 100 for percentage!)
Out of all four stages of mitosis, which one takes the most time to complete? The shortest time? What happens to the process if we skip metaphase?
Exercises
- What is mitosis?
- What are the four stages of mitosis? Briefly describe what happens in each.
- Out of all four stages of mitosis, which one takes the most time to complete? The shortest time? What happens to the process if we skip metaphase?
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Iodine binds with starch and can be used to see the cytoplasm with white and yellow onions. If you don’t have iodine, use a red onion which is already pigmented naturally. You can stain the nuclei using one drop of methylene blue, but you should not let kids handle this as it’s a toxin.
The stain isn’t working. Did you have success with Iodine? On-line I read that Methylene blue binds with DNA and makes the chromosones visible. I can’t see anything, except cell walls, wit iodine.
It sounds like your technique is correct. By not heat mounting the slide, you should be able to see cell division happening. Even if you don’t, you’ll still be able to see a very cool image of cells in various stages of mitosis. When you think about how small cells are, and the fact that your microscope is a fairly simple tool, this is kind of remarkable (at least I think so). As discussed in the lab, seeing the stages of mitosis will allow you to make some conclusions about the relative length of time the cell is in each stage of this process.
As far as the size of the cut, you’ll want it to be thin enough that it appears translucent; otherwise you’ll have a hard time seeing it through the compound microscope. A razor blade is a good tool for this, as long as you are very careful of course.
Another question to check before we do this to avoid messing it up. Am I correct that we are to cut a very narrow cross section off of the root (right near the cap), then cut that cross section in half length-wise? And, if we put that piece on our slide and stain it, we should hopefully see the cell division process happening (if we don’t heat mount it). Finally, how skinny should a cross section be to be able to see cell division, and is the best cutting device a razor blade for skinny cuts? Thanks!
Yes, you can try a green onion’s root tip and see what it looks like. For the video question, have you always had this issue, or is this new? is it just this video or all of them?
Hi Aurora, Is it OK to use a green onion for this experiment? (the skinny kind) Also, I am getting an error message when I try to play the video my browser (Firefox). Thank you!