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Why Do Cells Divide? Why Do Cells Divide? 1. Surface area to volume ratio 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 Cell Size 1 cm x 1 cm x 6 = 6 cm2 2 cm x 2 cm x 6 = 24 cm2 3 cm x 3 cm x 6 = 54 cm2 Volume (length x width x height) 1 cm x 1 cm x 1 cm = 1 cm3 2 cm x 2 cm x 2 cm = 8 cm3 3 cm x 3 cm x 3 cm = 27 cm3 Ratio of Surface Area to Volume 6/1 = 6:1 Surface Area (length x width x 6) © Pearson Education, Inc. 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. 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. 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. chromosomes Genes (DNA) Chromatids (Sister) One of two identical parts of a duplicated chromosome Centromere Sister chromatids Number of Chromosomes Fruit Flies: 8 Carrots: 20 Humans: 46 Fern: 480 White Ash: 138 Turkey: 82 Human Karyotype HUMAN CHROMOSOMES Genetic Abnormalities The Cell Cycle © Pearson Education, Inc. Next… we will learn about DNA.