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Cell Size Limits: Understanding the Constraints of Cellular Growth

Explore the reasons why cells cannot grow infinitely in size, from diffusion and DNA limitations to surface area-to-volume ratio challenges. Learn how cells overcome these constraints through division.

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Cell Size Limits: Understanding the Constraints of Cellular Growth

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  1. Cell Size Limitations Why are cells so small?

  2. Why can’t organisms be one big giant cell?

  3. Diffusion limits cell size • Movement from higher concentration to lower concentration • Larger the distance, slower the diffusion rate • A cell 20 cm (8in) would require months for nutrients to get to the center • This is about the size of a dinner plate • http://www.youtube.com/watch?v=M30PrtZDB8I

  4. DNA limits cell size • Larger cells need more DNA. • They need more of everything! • Most cells have just one nucleus. • There is not enough DNA to make all the stuff a cell needs if it gets too big. • DNA Replication is complicated: • http://www.youtube.com/watch?v=bW5JnYZImJA • http://www.youtube.com/watch?v=teV62zrm2P0

  5. Surface area to volume ratio limits size

  6. As volume increases, the surface increases. • The problem is that the volume increases more rapidly than surface area. • Cell size doubles, 8x as much volume, but only 4x as much surface area • http://www.youtube.com/watch?v=xuG4ZZ1GbzI

  7. So, if too big is a problem, what’s the solution? • Cells divide before they become too big • Process of cell division is called mitosis

  8. TO RECAP: • 1. Diffusion limitscell size • Slow and inefficient over large areas • 2. DNA limits cell size • Limit to how quickly DNA can be read • Limit to # of proteins built / period of time • 3. Surface area to volume ratio limits cell size • Volume increases faster than surface area • Requires more nutrients, get rid of more wastes but through a relatively smaller surface area – • it is more difficult for things to get in and out!

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