Learning Objectives
Having completed the lab on mitosis, you should be able to:
- define the following terms: chromosome, spindle, centromere, centrosome, gametes, somatic, cytokinesis, cleavage furrow, homologues (homologous chromosomes),
- list the stages of the cell cycle in order
- describe the cellular events that occur during interphase (be sure to include the specific portions of interphase such as G1, S and G2)
- describe the overall process of mitosis (what is the purpose and the outcome of mitosis)
- describe the events of prophase of mitosis
- describe the events of metaphase of mitosis
- describe the events of anaphase of mitosis
- describe the events of telophase of mitosis
- explain what is meant by a diploid chromosome number versus a haploid chromosome number
- if given the chromosome number of the parent cell, determine what the chromosome number of the daughter cells would be after mitosis
Slideshow
Introduction
According to the cell theory of biology, all cells arise from pre-existing cells. In eukaryotes, this generally occurs by the process of mitotic cell division, which involves the separate but often coordinated processes of cytokinesis (division of the cytoplasm and organelles) and mitosis (division of the nucleus and associated DNA). Mitosis without the co-occurance of cytokinesis leads to the production of multinucleated cells, such as those found naturally in skeletal muscle and cardiac muscle. Mitotic cell division leads to the production of genetically identical daughter cells from existing parent cells. Mitotic cell division is used in asexual reproduction, growth, and repair. Meiosis is another form of cell division in eukaryotes that leads to the production of gametes. While the process of mitosis is continuous process within the cell cycle (i.e., it doesn’t occur in discrete steps), biologists are classifiers and tend to place things into discrete categories. Mitosis is commonly divided into four major phases: prophase, metaphase, anaphase, and telophase. You may find that some accounts of mitosis further subdivide the process to include prometaphase between prophase and metaphase. In this exercise, we will consider prometaphase a component of prophase.
Part 1. Mitosis Diagram
Using Figures 1–4, diagram the phases of mitosis and in the space provided to the right, describe the events of each phase using a chromosome number of 6 (2n = 6).
Figure 1. Prophase
Figure 2. Metaphase
Figure 3. Anaphase
Figure 4. Telophase
Introduction
In plants, cell division cell division generally takes place in meristematic tissues where the plant is actively growing, at the apex of roots and shoots. An onion root may be divided roughly into four regions:
- the root cap-protective tissue composed largely of dead cells
- meristematic tissue-rapidly dividing cells located just behind the root cap
- elongating cells-located immediately behind the meristematic tissue
- mature and specialized cells-root hairs and other plant tissues
You will be examining cells of the meristematic tissue, located just behind the root cap at the tapered end of the root tip.
Materials
- Compound microscope
- Onion root tip slide
Procedure
- In Figure 5 below, identify the phase of mitosis and write the name of the phase below each diagram. The cells go in the appropriate temporal sequence through cell cycle and you are likely to use the same term multiple times. While technically not a phase of mitosis, you may use “interphase” for some of the cells, but you should not use “cytokinesis.”
- Hold the slide of the onion root up to the light and note that there are several longitudinal sections on the slide. Examine all sections on the slide. Locate the meristematic tissue to observe phases of mitosis using high power.
- Find each phase of mitosis on the slide. As you locate each phase, your instructor will verify that you are correct and initial your paper. After you have received verification from your instructor, draw the cell in Table 1.
Figure 5. Mitosis in the onion root tip
| Table 1. Find, identify, and draw the phases of mitosis in the onion root tip and whitefish blastula. | ||
|---|---|---|
| Onion Root Tip | Whitefish Blastula | |
| Prophase |
|
|
| Metaphase |
|
|
| Anaphase |
|
|
| Telophase |
|
|
Mitosis in the Whitefish Blastula
Introduction
Materials
- Compound microscope
- Prepared slide of whitefish blastula
Procedure
- In Figure 6, identify the phase of mitosis and write the name of the phase below each diagram. The cells go in the appropriate temporal sequence through cell cycle and you are likely to use the same term multiple times. While technically not a phase of mitosis, you may use “interphase” for some of the cells, but you should not use “cytokinesis.”
- Hold the slide of the whitefish blastula to the light and note that there are a number of sections on the slide. Examine all sections on the slide using high power to locate all the phases of mitosis.
- Find each phase of mitosis on the slide. As you locate each phase, your instructor will verify that you are correct and initial your paper. After you have received verification from your instructor, draw the cell in Table 1.
Figure 6. Mitosis in the whitefish blastula.
Questions
- How does cytokinesis differ between plant cells and animal cells?
- What specific functions occur during interphase that prepare the cell for division. (These cannot be observed with the light microscope.)
- Label Figure 7 with the stages of cell cycle (interphase, G1, S, G2, M).
