WHY DO CELLS DIVIDE?

IT’S ALL ABOUT SIZE

THERE IS AN UPPER LIMIT TO HOW LARGE A CELL CAN BE

WHY DO CELLS DIVIDE? 1.Diffusion

WHY DO CELLS DIVIDE? 1.Diffusion 2.DNA

WHY DO CELLS DIVIDE? 1.Diffusion 2.DNA 3.Surface area-to-volume ratio

WHY DO CELLS DIVIDE? 1.Diffusion –A cell must move all materials needed for functioning via diffusion through cytoplasm

WHY DO CELLS DIVIDE? 1.Diffusion –A cell must move all materials needed for functioning via diffusion through cytoplasm –It takes a fraction of a second for materials to move from the plasma membrane to the center of a typical cell with a diameter of 20 µm

WHY DO CELLS DIVIDE? 1.Diffusion –A cell must move all materials needed for functioning via diffusion through cytoplasm –It takes a fraction of a second for materials to move from the plasma membrane to the center of a typical cell with a diameter of 20 µm –If a cell were 20 cm in diameter, it would take months to move materials from the plasma membrane to the center of the cell

WHY DO CELLS DIVIDE? 2.DNA –A cell must respond to changing conditions rapidly

WHY DO CELLS DIVIDE? 2.DNA –A cell must respond to changing conditions rapidly –A cell frequently needs to produce large amounts of proteins and enzymes

WHY DO CELLS DIVIDE? 2.DNA –The process by which proteins and enzymes are made is complicated DNA makes an RNA copy of the gene to be copied RNA leaves the nucleus and travels to a ribosome RNA directs protein production at the ribosome

WHY DO CELLS DIVIDE? 2.DNA –If there is not enough DNA to rapidly carry out RNA production, the metabolism will slow and the cell will die

WHY DO CELLS DIVIDE? 2. DNA Larger cell = greater metabolism

WHY DO CELLS DIVIDE? 2. DNA Larger cell = Greater metabolism Greater metabolism = More DNA needed to direct metabolism

WHY DO CELLS DIVIDE? 3.Surface area-to-volume ratio –As the size of any object increases, volume increases at a much greater rate than does surface area

WHY DO CELLS DIVIDE? 3.Surface area-to-volume ratio –As the size of any object increases, volume increases at a much greater rate than does surface area –A cell receives all the materials needed for life through its plasma membrane

WHY DO CELLS DIVIDE? 3.Surface area-to-volume ratio –Larger organisms (or cells) need more “stuff”: you require more food than does a two-year-old human

WHY DO CELLS DIVIDE? 3.Surface area-to-volume ratio –Larger organisms (or cells) need more “stuff”: you require more food than does a two-year-old human –As the volume of a cell increases, it needs more and more materials to be passed through the plasma membrane in order to sustain life

WHY DO CELLS DIVIDE? 3.Surface area-to-volume ratio –At some point, there will not be enough surface area on the plasma membrane to absorb the required amount of materials necessary for life