view an onion root tip and calculate the percentage of cells at each of the stages of cell division.
Introduction
The time and events that occur between one cell being newly created and then dividing are known as the cell cycle. Each generation of new cells undergoes the same events of division of nuclear and cytoplasmic materials, cell growth and cell maturation. The ultimate end result of a mature cell may be to divide, to die a programmed death (apoptosis) or become differentiated and probably never divide again.
Mitosis takes up a relatively small amount of time in the total life cycle of a cell. Most of the time a cell is engaged in normal living, growing, building and replicating it s DNA. This preparation stage is known as interphase. If a cell is to divide successfully then its DNA must be duplicated exactly during interphase and the two copies of each chromosome are stuck to each other along their length. Thus, for some period of time, a human cell actually contains 46 pairs of chromosomes.
Mitosis is a type of nuclear division along with meiosis. Mitosis consists of a series of continuous movements of the chromosomes until they have been evenly divided into two newly forming cells. Usually as the events of mitosis are coming to a close the cytoplasm begins to divde, a process known as cytokinesis.
I. Mitosis Tutorial
On the left side of the screen is a navigation bar, click on the link listed as "ACTIVITIES" Go to “MITOSIS” and then "THE CELL CYCLE." Read the text on each page and view the animations. You can slow down the video by clicking step by step through the phases.
Watch the video carefully.
1. The colored chromosomes represent chromatids. There are two of each color because one is an exact duplicate of the other.
--How many chromosomes are visible at the beginning of mitosis?
-- How many are in each daughter cell at the end of mitosis?
The little green T shaped things on the cell are centrioles.
-- What happens to the centrioles during mitosis?
This site provides a nice review of the phases in the onion.
This
site shows the phases in the whitefish.
II. Onion Root Tip - Online Activity
Read the introduction, then click the “next” button.
You will have 36 cells to classify. When you’re finished, record your data in the chart below.
| Interphase | Prophase | Metaphase | Anaphase | Telophase | Total |
Number
of cells | __________ | __________ | __________ | __________ | __________ | 36 |
Percent
of cells | __________ | __________ | __________ | __________ | __________ | 100% |
**To calculate percent: number of cells in phase/ total number X 100
Assignment:
1. Fill in the chart and complete the calculations.
2. Based on the results you just calculated, what fraction of the total cell cycle was taken up by mitosis?
3. Identify the differences between mitosis and cytokinesis in plant and animal cells. Indicate differences in structures involved, sites where it occurs within the organism, or difference in how cytokinesis may appear as it is occuring.
4. What role does mitosis play in the life of a multicelled eukaryote?
5. How is binary fisssion in a prokaryote different from mitosis in a eukaryote? This site may help in answering the question.