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Surface Area Limits Cell Size And Cell Reproduction • Diffusion limits cell size. • Diffusion is fast and efficient over short distances, but becomes slow and inefficient as the distances become larger. • Imagine a mitochondrion at the center of a cell with a diameter of 20 cm. It would have to wait months before receiving molecules entering the cell. • DNA also limits cell size. • Recall that DNA has the blueprints for proteins, and proteins are used by almost every organelle to perform their function. • But there is a limit to how quickly these protein blueprints can be copied and made into proteins. • The cell can not survive unless there is enough DNA to support the protein needs of the cell. • In larger cells such as a large amoeba, there is more than one nucleus in order to supply the necessary amounts of proteins need by the cell. • Surface area-to-volume ratio is another limiting factor. • As the cell’s size increases its volume increases much faster than its surface area. • If a cell doubled in size it would require eight times more nutrients and would have eight times more waste to excrete. The surface area by contrast would only increase by a factor of four. • Ultimately making it so that the plasma membrane didn’t have enough surface area though which oxygen, nutrients, and wastes could diffuse. Cell Reproduction • There are many reasons cells reproduce: – Old age – Injury – Too big – Constantly worn out (ex: intestines) Just to name a few • But it all follows the same process. • Two main parts interphase and mitosis, but these two parts can be broken down further. – Interphase has 3 parts to it – Mitosis has 4-5 stages to it Cell Cycle • There are five main parts to the cell cycle: – G1-Growth 1(GAP 1), this is when the cell increases its size, new proteins and organelles are made – S-Synthesis, once the cell is big enough it triggers the replication of DNA so there are now two copies of DNA in the nucleus – G2-Growth 2 (GAP2), In preparation for cell division the cell grows even more so the new cells will have enough material to survive (Low SA to V ratio) – Mitosis- The process of equally distributing chromosomes into two nuclei. – Cytokinesis-The process of actually splitting the cell into two each with a nucleus and enough organelles to survive.