Onion Root Cell Cycle Lab Answers

Introduction

Every somatic cell undergoes a phase called mitosis. Mitosis is the division of the nucleus to form two genetically identical nuclei. There are four phases of mitosis: prophase, metaphase, anaphase and telophase.

Prior to mitosis is interphase (when the cell grows and duplicates all organelles), and post-mitosis is cytokinesis (when the cell membrane pinches together to split the actual cell in half to form two cells (animal) or when a cell plate is formed to separate the cells (plant)). Cells divide to replace old, dead cells, to grow and to reproduce new organisms.

Hypothesis

It can be predicted that all somatic cells will undergo all the stages of mitosis multiple times in their lifetime, that the viewed will be able to see the chromosomes at one stage of mitosis. Finally, it is predicted that the cells will not look large or clear, but it will still be able to give me a general idea of what is going on.

Materials

• The materials that were used in this lab are:
• Microscope (with 40X, 100X and 400 X magnifications)
• Prepared microscope slide of an onion root tip
• Prepared microscope slide of a whitefish embryo

Observations

When observing the onion root tip cells for the stage of prophase, the cells took on a brick-like structure and within the cells, small dots (the nuclei) can be seen. In one particular cell’s nucleus, the chromatin has condensed so much that it can be seen using a light microscope.

The stage that the cell is currently in is prophase. Also, the cell walls in the onion root were barely visible, but the nuclei were very clear. This was all seen in 400X total magnification.

When observing the whitefish embryo cells for the stage of metaphase, the cells took on a circular shape and, like the onion root cell, many nuclei can be seen. In a certain cell, the chromatin, that was condensing during prophase, line up at the equatorial plate. That certain cell is in the metaphase stage.

This was, like the onion root cells, viewed at 400X total magnification. When observing the whitefish embryo for the stage of anaphase, the overall cell shape stayed the same and they still had a circular shape.

In a certain cell, the chromosomes (condensed chromatin), that were lined up in the previous stage, break apart from their duplicates and head towards opposite centrioles. The stage that the cell is currently in is anaphase. Like the last two specimens, this was viewed in 400X magnification.

When observing the whitefish embryo cells for the stage of telophase, the overall shape stayed the same except for one cell which is currently in the telophase stage. The cell that is in the telophase stage looks like two circular cells joined together. In this stage, the chromosomes reached the centrioles and a nuclear membrane begins to form around each nucleus. This was also viewed at 400X magnification.

Discussion

If a mother cell has 10 chromosomes, each daughter cell will also have 10 chromosomes. The mother cell duplicates its chromosomes so that each daughter cell will receive the exact number that they originally have.

Percentage of cells= (# of cells showing mitosis) /Total cells observed x 100

• 25% of the cells are in the prophase stage
• 5% of the cells are in the metaphase stage
• 5% of the cells are in the anaphase stage
• 5% of the cells are in the telophase stage
• 40% of the cells are in a stage of mitosis

Conclusion

Furthermore, the stated hypothesis is correct. It states that all somatic cells will undergo the stages of mitosis multiple times throughout their overall lifetime and they do. It stated that the viewer will be able to see the chromosomes in one stage of mitosis and, during the prophase, metaphase, and anaphase stages, the viewer is able to see the chromosomes.

The final statement is that the cells seen using the microscope will not be very large or clear, but it will be sufficient enough for a general idea of what is going on.

That final statement is also correct because the cells were very small and unclear, but the viewer is able to see what is taking place.

Overall, I have learned that onion root tip cells and whitefish embryo cells are constantly reproducing and creating new cells, how to calculate the percentage of cells in a stage of mitosis, and, finally, that the chromosomes are visible using only a light microscope.