Module 5 Lesson 2 - 5
Lesson 2 - Mitosis
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Investigating Cells in Mitosis
Observation of cell division live is difficult. However, some tissues in plants or animals are undergoing such rapid growth that observation of that area under a microscope can reveal several cells frozen in a stage of division. A common area to investigate is the tips of roots.
Tip: Cells that are dividing have condensed chromosomes; therefore, they appear as small dark worms instead of a vague mass. To record your observation, place the pointer on one dividing cell and take a screen capture to save your findings.
- Click the image above to an interactive online microscope.
- Choose "onion root tip, mitosis" in the specimen area. There are two different slides you can observe
- To see different parts of the slide, move the field of view located in the mini screen (top right corner of the screen).
- Explore this slide under various magnifications.
- Try to locate cells that are dividing.
- Screen capture cells in prophase, metaphase, anaphase, telophase, and cytokinesis.
- Save the images in a document to help you understand the mitotic phase.
Reasons and Limits for Cell Growth
Read pages 560 - 561
Several factors may lead cells to reproduce. The most common stimulation is the need for replacement due to damage or age. Cells work very hard, and many become too brittle or build up toxins too quickly to continue to function. These cells are broken down by the body and their raw materials are re-used.
When the call for cell reproduction is given, how do cells know when to turn off? Consider skin cells as a working example. Your skin is one of the most active areas on your body for cell reproduction. Skin cells use two common clues to determine when to start or stop reproduction. The first is density-dependent inhibition.
For density-dependent inhibition to work, cells must be attentive to their neighbours. First, regular skin cells will not divide if alone. Next, if a gap occurs in a layer of skin cells, those that remain automatically begin to divide until the gap is covered. Also, when skin cells bump up against their neighbors, they stop dividing.
Another clue that cues cell growth is anchorage dependence. Again, consider skin cells as the example; skin grows naturally if anchored to an underlying layer of tissue. Conversely, skin cells will not grow if they are free-floating in a nutrient bath.
Cancer
Cancer is a broad group of diseases characterized by rapid, uncontrolled division of cells. Cancer cells appear to ignore all the regulations in place for cell growth. They do not wait or stop at any of the checkpoints. They do not appear to be density-dependent, nor are they anchorage-dependent. Cancer cells grow and reproduce constantly.
Metastasis is cancer cells leaving their original sites. After cancer cells begin to spread in this fashion through the blood or lymphatic systems, it becomes more difficult to get rid of them.
Watch and Listen
Consider the following animations on cancerous growth. The first animation shows how a cancerous growth might occur. Another very dangerous characteristic of cancer is shown: its ability to spread. (Source: Cell Biology and Cancer at National Health Institute)