Onion Root Tip Mitosis

INTRODUCTION

In this experiment, we will be using on onion root tip to show the different stages of mitosis. According to the National Human Genome Research Institute, “Mitosis is the process where the cells replicate their chromosomes and then segregates them, producing two identical nuclei in preparation for cell division.” Mitosis is very important to every living organism. Humans use mitosis to create more skin cells, blood cells, muscle cells and more.

Mitosis occurs through different stages. These stages are Prophase, Metaphase, Anaphase and Telophase. The reason why we are using an onion in this experiment is because their root tips grow at a rapid rate due to rapid cell division, which allows us to identify the different stages of mitosis.

In the Results section in the procedure, there will be further explanation on what each stage will look like.

Here are vocabulary terms to be familiar with (click on the word to be taken to the National Human Genome Research Institute website for their definitions):

Nucleus

Chromatin

Cell Cycle

Chromatid

Centromere

TECHNICAL BACKGROUND

In order to understand how to do this experiment, you will need to have background on how to work a microscope and how to prepare 1M solution on HCL.

WARNINGS, CAUTIONS, AND DANGERS

  • Wear goggles, gloves and lab coat
  • Sharp Objects
  • Hot surfaces
  • This experiment is not edible

EQUIPMENT

  • Glass/Plastic Jar
  • Toothpicks
  • Blade/Scalpel
  • 2 Petri Dish or Small Clean Container
  • Medium to Large Glass
  • Hot Plate/ Stove
  • Small Bottle
  • Thermometer
  • Forceps
  • Vial with Cap/Lid
  • Microscope Glass Slide
  • Dissection Needle
  • Coverslip
  • Microscope
  • Stop Clock
  • 70% Alcohol

 

SUPPLIES

  • Onion
  • Water
  • 1M HCL
  • Stain (acetic orcein or aceto-carmine)

 

PROCEDURE

Growing Onion Roots:

  1. Pour water into a clean, clear glass/plastic jar. Fill it about 3/4 full.
  2. Place the onion bulbs in the jar so that only the lower surface of the onion comes into contact with the water. (If the onion is too small, place toothpick into the onion to keep the only the lower surface in the water and the rest above.)
  3. Let the onions rest on water for 3-4 days.

Sample Preparation:

  1. Using a blade or scalpel, carefully cut one or several roots from the onion and place them in petri dish or any small clean container.
  2. In a medium to large glass container, prepare a water bath.
  3. If able, set your hot plate to 55 degrees C and place your water bath on it. If you do not have a hot plate, heat your water bath to a stable temperature of 55 degrees C.
  4. Carefully pour the hydrochloric acid solution into a small bottle and place it in the water bath for about 15 minutes to warm the acid.
  5. Using the forceps, carefully pick one or two of the roots and place then into the bottle of warm hydrochloric acid for about 5 minuets.
  6. Remove the roots form the bottle of acid using the forceps and rinse them with tap water several times.
  7. Place the root tips into a clean petri dish.
  8. Using a clean blade, cut off the tips of the roots. (about 5 mm in length)
  9. Using the forceps, pick the root tips and put them in the vial of stain. (acetic orcein or aceto-carmine)
  • Make sure the root tips are completely in the stain.
  1. Place a cap/lid on the vial and make a prick hole through the cap/lid.
  2. Place the vial in the water bath for about 5 minutes.
  3. Using the forceps, remove the root tips from the vial of stain and place them onto a clean microscope glass slide.
  4. Using a dissection needle, gently mash/squash the root tips to spread out the cells on the glass slide.
  5. Cover the glass slide with a coverslip and gently press the coverslip down.
  6. Examine the slide under the microscope.

Results:

Viewing slides under 10x magnification:

Students should be able to observe several single layers of cells.

  • Note: This magnification will not show the stages of mitosis. It will show a row of cells the generally consists of 2 and 5 cells.

Viewing slides under higher magnification (100x-500x)

Students should be able to observe the different stages of mitosis under higher magnification.

The stages that should be visible are:

Interphase

Interphase is not a part of mitosis, but it is the preparation step. Interphase includes G1, which is characterized by cells growth, S phase, which is where the DNA is replication, and G2, which is where the cells prepares to enter mitosis or M phase.

The way to identify interphase is to notice that the chromatin is not tightly packed.

Prophase:

Prophase is the first step of mitosis. In prophase, the chromatids form together to make the chromosomes. These chromatids that are formed together are called the sister chromatids, which contain the same genetic information and are attached at the centromere. Another important structure that is forming is the mitotic spindle. This structure will be important during a later stage.

During this stage, the nucleolus is still visible, but the nucleus is grainy due to chromosomal condensation.

Prometaphase

This is the second stage of mitosis. During this stage the chromosomes are still condensing, but the nuclear envelope is broken down. Not only are these things happening, but kinetochore start to develop around the centromere.

Metaphase

This is the third stage of mitosis. During this stage, the sister chromatids align along the middle of the cell, preparing for the sister chromatids to be separated. The chromosomes, during this stage, become more visible. Also, the fully developed spindle fibers, located on two different sides of the cell, attach to each of the sister chromatids.

Anaphase

This is the fourth stage of mitosis. During this stage, the two sister chromatids start separating and moving towards the opposite side of the cells.

 

Telophase

This is the fifth and final stage of mitosis. During this stage, many different events are taking place. The chromosomes are at the opposite ends of the cell, the breakdown of the spindle fibers begin, the development of the nuclear envelope starts to form around the two sets of chromosomes that are on the opposite ends of the cell, and the DNA starts to de-condense.

Cytokinesis

This step is not a part of the the mitosis phase, but is followed directly after this. During this step, the cytoplasm separates as the cell divides into two identical daughter cells, but since plat cells have cell walls that prevent them from pinching apart, we are not able to see this happening.

Disposal:

Dispose of all solid waste in the trash and all liquid waste can be disposed down the drain with lots of water.

 

Helpful Video:

Sources:

“Mitosis.” Genome.Gov, www.genome.gov/genetics-glossary/Mitosis. Accessed 12 May 2024.

Microscope Master. “Onion Root Tip Mitosis.” Microscope Master, Microscope Master, n.d., www.microscopemaster.com/onion-root-tip-mitosis.html.