Why Do Cells Divide?

Why Do Cells Divide? 1. Surface area to volume ratio Efficiency of moving materials into the cell Efficiency of moving materials into the cell –The larger the cell becomes the less efficient it is –The volume of the cell increases faster then its surface area –Cells that grow too large no longer have enough surface area to take in nutrients and remove waste

Ratio of Surface Area to Volume in Cells © Pearson Education, Inc. Cell Size Surface Area (length x width x 6) Volume (length x width x height) Ratio of Surface Area to Volume 1 cm x 1 cm x 6 = 6 cm 2 2 cm x 2 cm x 6 = 24 cm 2 3 cm x 3 cm x 6 = 54 cm 2 1 cm x 1 cm x 1 cm = 1 cm 3 2 cm x 2 cm x 2 cm = 8 cm 3 3 cm x 3 cm x 3 cm = 27 cm 3 6 / 1 = 6 : 1 24 / 8 = 3 : 1 54 / 27 = 2 : 1

2. Cells get old and worn out Just like anything else, cells get worn out. They need repair, and, just like an old car, eventually need replacement. Just like anything else, cells get worn out. They need repair, and, just like an old car, eventually need replacement. The best way to fix what ails a cell is to replace that cell all together. The best way to fix what ails a cell is to replace that cell all together.

What does a cell need to do first? In order to reproduce, a cell must make copies of its DNA and organelles. The new cell needs all the stuff the old cell has.

DNA DNA must be copied in a process called DNA replication. DNA must be copied in a process called DNA replication. After replication, the DNA is all stringy and tangled (called chromatin), but must be separated into a new cell. Before this can happen, the DNA must coil up into chromosomes. After replication, the DNA is all stringy and tangled (called chromatin), but must be separated into a new cell. Before this can happen, the DNA must coil up into chromosomes.

Chromosomes Threadlike structures made up of DNA that coils around proteins. Contains genetic information that is passed form parents to offspring. Threadlike structures made up of DNA that coils around proteins. Contains genetic information that is passed form parents to offspring. chromosomes Genes (DNA)

Chromatids (Sister) One of two identical parts of a duplicated chromosome One of two identical parts of a duplicated chromosome Centromere Sister chromatids

Number of Chromosomes Fruit Flies: 8 Fruit Flies: 8 Carrots: 20 Carrots: 20 Humans: 46 Humans: 46 Fern: 480 Fern: 480 White Ash: 138 White Ash: 138 Turkey: 82 Turkey: 82

Human Karyotype HUMAN CHROMOSOMES

Genetic Abnormalities

The Cell Cycle © Pearson Education, Inc.

Next… we will learn about DNA.