Cell Growth & Reproduction

Cell Sizes *usually 2-200 micrometers in diameter (whale & mouse cells are about the same size- how?) *cell range in size from 8 micrometers to 1 meter long to 8 centimeters  size related to function, not organism (nerve cells long to relay messages, blood cells fit through arteries) *cells don’t just increase in number, they become specialized

http://learn.genetics.utah.edu/content/begin/cells/scale/

http://www.bio.miami.edu/~cmallery/150/proceuc/c18x1cell-size-compare.jpg

Cell Size Limitations - #1 Why diffusion limits cell size: a. cells need plenty of glucose & oxygen to make energy & to get rid of CO2 & waste b. it takes a fraction of a second for oxygen to travel about 20 nanometers to innermost mitochondrion c. if a cell were too big, diffusion of needed nutrients would take too long. Ex: if a cell were 20 cm, it would take months for a molecule of oxygen to get to the mitochondria & the cell would die

Cell Size Limitations - #2 Why a cells DNA content limits cell size: a. most cells contain only one nucleus that contains DNA. If a cell doesn’t have enough DNA to control it, the cell will die b. if a cell is very large, it must have more than one nucleus so it has enough DNA

Cell Size Limitations - #3 Surface area to volume ratio: a. as a cell size increases, volume increases faster than surface area Ex: If cell surface area = 6mm2 (1mm sides), volume = 1mm3 If cell surface area = 24mm2 (2mm sides), volume = 8mm3 b. Is big better? If a cells surface area does not increase in proportion to volume there would not be enough surface area through which nutrients & oxygen to enter

Why Most Cells Are Small: http://staff.jccc.net/pdecell/cells/cellsize.html

four surface area eight volume The surface area of the cell will increase by four. The volume will increase by eight. it divides

http://bio1151b.nicerweb.com/doc/class/bio1151/Locked/media/ch06/06_07SurfaceVolumeRatio_L.jpg