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As with anything that is taking place within a cell, the metabolic waste too must be proportional to the size of the cell. In particular the surface area to volume ratio. But how is the waste excretion related to the concept of above ratio and how to determine it?

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  • $\begingroup$ @AliceD Yes it's an active mechanism. I am not sure about the compounds, but this is a type of a question that was asked in a pre-college course material right after introducing the two main cell kinds. And I am just starting to scratch a tip of an iceberg - reckon...as bio is a new area for me. $\endgroup$ – bonCodigo Mar 30 '15 at 8:51
  • $\begingroup$ If smaller cells have any measures to cope with waste then large sized cells should have that mechanism improved much more to facilitate the extra waste production. This is an opinion. $\endgroup$ – Jayachandran Mar 30 '15 at 11:09
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    $\begingroup$ @Jay - no that is a wild guess :) $\endgroup$ – AliceD Mar 30 '15 at 11:28
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    $\begingroup$ @Alice and Jay: this is where the question is listed., page 16. As far as what I understood, the larger animals don't mean larger cells but more cells. The question is pretty confusing to me. And btw, I didn't add that last sentence, someone else seemed to have editted it... $\endgroup$ – bonCodigo Mar 30 '15 at 12:57
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The critical element here is that building materials that need to be absorbed, or waste materials that need excretion have to cross the cell membrane. The larger the surface of the cell's membrane relative to its volume, the faster the exchange rate.

The book section you linked in the comments mentions the following on p.14:

The volume [of a spherical cell] increases by a factor calculated by cubing the radius, [...] the surface area increases by a factor calculated by squaring the radius. [...] This means that a large cell has relatively less surface area to bring in needed materials and to rid the cell of waste [...]. Cells are limited as to the size they can attain [...]. Cells that are larger [...] have modifications that allow them to function efficiently. This is accomplished by shape changes such as from spherical to long and thin, [or] have infoldings or outfolding to increase their surface relative to their volume.

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  • $\begingroup$ I guess this concept is trying to convey the message why cells are small or why cells are made small and how cells take different shape to maintain this ratio? $\endgroup$ – bonCodigo Mar 31 '15 at 4:07
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    $\begingroup$ @bonCodigo - yes correct, as well as how they can grow big and still be functional. $\endgroup$ – AliceD Mar 31 '15 at 4:09

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