WHY DO CELLS DIVIDE? 10-1

WHY DO CELLS DIVIDE? IT’S ALL ABOUT SIZE

WHY DO CELLS DIVIDE? (instead of just getting bigger) Diffusion DNA Surface area-to-volume ratio

Diffusion Cells need: food and oxygen to eliminate wastes to move all materials through cytoplasm

Diffusion Typical cell has a diameter of 20 µm takes a fraction of a second for materials to move from cell membrane to the center of the cell If it had 20 cm diameter would take months to move materials same distance The cell would die from starvation or poisoning from wastes before it got that big

DNA Cell needs: to respond to changing conditions rapidly to produce large amounts of proteins and enzymes

DNA DNA directs the production of proteins and enzymes DNA makes an RNA copy RNA leaves the nucleus and travels to a ribosome RNA directs protein production at the ribosome

DNA If there is not enough DNA to control the cell the metabolism will slow and the cell will die

WHY DO CELLS DIVIDE? (instead of just getting bigger) DNA Larger cell = Greater metabolism

DNA Larger cell = Greater metabolism Greater metabolism = More DNA needed to direct metabolism

Surface area-to-volume ratio As size of a cell increases, volume increases at a much greater rate than does surface area

Surface area-to-volume ratio Cell needs: materials for processes obtains materials through its cell membrane larger organisms (or cells) need more “stuff” more and more materials as its volume increases surface area for absorbing required materials (not enough surface area to supply the needs for larger cells)

Surface area-to-volume ratio Example: Surface area of a cube = area of 1 side x 6 Area of 1 side = length x width 1 inch = 1 in x 1 in = 1 in2 Surface area = 1 in2 x 6 = 6 in2

Surface area-to-volume ratio Example: Volume of a cube = length x width x height = 1 in x 1 in x 1 in 1 inch = 1 in3

Surface area-to-volume ratio Example: Surface area = 6 in 2 1 inch Volume = 1 in3 Surface area : Volume ratio = 6 : 1

Surface area-to-volume ratio Example: Surface area of a cube = area of 1 side x 6 Area of 1 side = length x width = 4 in x 4 in 4 inches = 16 in2 Surface area = 16 in2 x 6 = 96 in2

Surface area-to-volume ratio Example: Volume of a cube = length x width x height = 4 in x 4 in x 4 in 4 inches = 64 in3

Surface area-to-volume ratio Example: Surface area = 96 in 2 Volume = 64 in3 4 inches Surface area : Volume ratio = 96 : 64 = 3 : 2

Surface area-to-volume ratio Example: 4 inches 1 inch Surface area : Volume ratio = 6 : 1 Surface area : Volume ratio = 3 : 2