2.4 Cell Cycle Lab & Quiz

Watch the video of the bean seed sprouting. Pay attention to the way the roots grow.

Onions have larger chromosomes than most plants. The chromosomes stain dark and are easily observed through a light microscope. Since the roots of an onion are going through rapid growth, the root cells spend much of their time in stages, or phases, of mitosis (cell division).

In this lab you will use a microscope to observe cells in the tip of an onion root. The cells have been frozen in time in different phases of their life cycle. Some of the cells will be in the middle of cell division. Your task will be to find cells in different phases of the cell cycle and draw those cells in your notebook.

Part 1

1. Put the diagrams of the different phases of the cell cycle in the correct sequence and set up your notebook page as shown.
2. Set up a microscope at your table. Refresh your knowledge on the parts of a microscope and how to use one safely and successfully.
3. Get an Onion Root Tip Mitosis prepared slide from your teacher.
4. Focus on one of the root specimens low power.
5. Move the slide until you have centered the END of one of the root tips. Focus on the cells near the tip of the root on MEDIUM and then HIGH Power. You will need to use high power for the rest of the lab.
6. Carefully move the slide around until you find an area that has cells that look different from each other. Try to find cells in each of the different phases of the cell cycle. The image shows where on the root tip you are likely to find cells that are in different phases.
7. From the microscope, sketch each phase of the cell cycle (interphase and phases of mitosis) that you see in your notes.
   1. Interphase
   2. Prophase
   3. Metaphase
   4. Anaphase
   5. Telophase & Cytokinesis
8. Once you have attempted to find all of the phases of mitosis on your own, compare your observations with the photos on this website. Use the photos to enhance your sketches if needed.
9. After you have finished your drawings for all 5 phases of the cell cycle, either clean up or continue on to Part 2 of the lab.

Part 2

1. Using a photo or the microscope, observe a region of an onion root tip. Look at the cells in different phases of the cell cycle.
2. Count and tally the cells in each of the phases of the cell cycle. Record the tally in the chart in your notebook. Refer to Part 1 of the lab to help you identify the phases. Note: sometimes the cells are in between phases and you will need to make a judgement call about which phase to call them. That’s okay!
3. Total up the number of cells found in the image. Use that number to find the percentage of cells in each phase of the cell cycle and record in the chart.
4. Create a pie chart that shows the percentage of cells in each phase of the cell cycle. Be sure to color code your pie chart and include a key or legend.
5. Once you have completed Parts 1 and 2 of the lab, take the quiz to check your understanding of the cell cycle.