Cell Size Limitations and Cell Division Cells come in different shapes and sizes, but most cells are between 2 and 200 micrometers in diameter.

Cell Size Limitations Cells do not grow very large because of: –The slow rate of diffusion the larger the cell, the longer it takes for molecules to diffuse through the cell membrane and cytoplasm – DNA DNA contains the blueprints for making proteins there is a limit to how quickly DNA can be copied and made into proteins if a cell gets too large, it might not have enough DNA to make proteins quickly enough

Cell Size Limitations (cont.) –Surface area-to-volume ratio as a cell’s size increases, it’s volume increases much faster than its surface area Think of the volume as the amount of cytoplasm; think of the surface area as the amount of cell membrane So the amount of cytoplasm (and nutrients needed and wastes created) increases faster than the amount of cell membrane; so there wouldn’t be enough surface area through which nutrients and wastes could diffuse The cell would starve to death or be poisoned from the buildup of wastes

Surface Area to Volume Ratio

Cell Division How do cells maintain optimum size? Cells divide before they get too large to function properly. Cell division – the process by which two identical cells are produced from one parent cell Cell division is important in repairing and replacing worn out or damaged tissues.

The Cell Cycle –The sequence of growth and division of a cell (the cell life cycle).

The Cell Cycle (cont.) Two main parts: Interphase – cell grows and performs normal functions; cells spend most of their time in this stage Cell division – the cell is dividing –This is how a single fertilized egg develops into a multicellular organism –How hair, skin, blood cells are replaced –How damaged cells are replaced –Some cells stay in interphase and do not divide – ex. Heart muscle cells, eye cells, brain cells

What happens during interphase? Interphase: G1 – (growth 1) –Cell grows and builds organelles –Cell begins performing its specific function for the body –Protein synthesis is high –Cell reaches optimum size S phase – (synthesis) –DNA is copied (DNA synthesis) G2 – (growth 2) –Cell grows and builds more organelles in preparation for division