Chapter 2.3 How Cells Reproduce

Cell Reproduction  All organisms, including you, begin life as a single cell.  One cell divides into two cells, those two cells divide into two cells.  This is how you have grown to your present size.

Stretch Your Mind  Starting from one cell, how many hours do you think it would take if a cell divides every hour to make one million cells?  Estimate,  Then calculate!

Regeneration  Many living things are able to grow new body parts to replace damaged or missing parts.  This ability to replace body parts is called regeneration.  Can we regenerate?

Human Regeneration  We cannot grow a new arm or leg, but when we scrape our skin or break a bone, our bodies regenerate the skin or bone to heal ourselves.  The cells in your skin wear out quickly and only live for days or weeks.  The nerve cells can last a lifetime.

Examples  Lizards can grow a new tail  Lobsters, newts, tadpoles, and insects can grow new legs.  Deer shed antlers each year and re- grow them.  Plants can re-grow their roots.

Mitosis  How does one cell become two?  You must observe the nucleus of the cell.  Some will not look like dark circles anymore but will have threadlike objects.  These are called chromosomes. They only become visible when a cell is about to divide.

Mitosis  Chromosomes contain the cell’s genetic material, or DNA. DNA contains the instructions for new cells to have the characteristics of the parents.  Mitosis is the process of when genetic material duplicates and divides into two identical sets of chromosomes.  The two new cells are called Daughter cells.

How rapidly do cells divide?  Different cells divide a different rates.  Bacterial cells divide once every 20 minutes.  Frog Embryos divide in about an hour.  Liver cells divide only once every 200 days.

Cells and Cancer  Cancer cells divide at a far greater rate than normal cells and they spread to other parts of the body.  “Mitosis gone Wild”  Cancer can be caused by the environment or personal habits.  Treatments are most successful in early detection.

Review  What are chromosomes?  What is mitosis?  Give an example of regeneration?  Why do cells of a multicellular organism continue to reproduce even after the organism is fully grown?

Review  How is a daughter cell like the original cell from which it formed?  How can you tell from a cell’s appearance alone whether the cell is undergoing mitosis?  APPLY: What evidence do you have that some cells in your body are dividing?