Cell Structures

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    • #10072
      Casey
      Participant

      Just looking through some exam papers and got a fright! Some of this stuff I havn’t a clue about and can’t find in my txt book!

      This question has come up in 2 of the papers I have looked through, it askes how the surface area of a cell changes as a cell grows?

      Also Cell Membranes. Things like what is the purpose of it, which is to keep all the organelles in that cell? Also what is the structure of a membrane like and how materials move in and out of the cell, by either passive of active transport.

      Anyone that can shed some light on these questions?

    • #85861
      mith
      Participant

      do a forum search.

    • #85866
      Casey
      Participant

      Thanks! That page helped a lot! 🙂 But I still can’t find how the surface area of a cell changes as a cell grows. Is it simply that as the cell gets bigger the surface area will get bigger too?

    • #85869
      blcr11
      Participant

      Surface area is proportional to the square of the radius. So surface area grows more rapidly than the diameter of the cell. If the radius doubles, the surface area quadruples. Volume grows even more rapdily than surface area. Volume is proportional to the cube of the radius, so if the radius doubles, the cell volume increases by a factor of 8.

    • #85872
      Casey
      Participant

      So if the radius doubles, the surface area increases by x4? then the volume increases by x8?

    • #85874
      blcr11
      Participant

      That’s about the size of it.

    • #85875
      Casey
      Participant

      Do you know how the it changes while the cell grows?

    • #85877
      blcr11
      Participant

      Not sure I understand the question. To get larger, you have to add material to the membrane (and even more to the interior)–or else you have to stretch things, but I don’t know if that’s what you mean.

    • #85878
      Casey
      Participant

      Is that why a cell can only grow to a certain size? Because the membrane would be too stretched and break?

    • #85879
      blcr11
      Participant

      I don’t think that’s the major determinant, though I suppose it can contribute to size limitation. Usually cells will grow until they touch another cell or group of cells, and then they stop growing. This is called contact inhibition and operates for most types of cells in solid tissues. Certainly, calorie restriction can limit cell growth, too.

    • #85880
      Casey
      Participant

      I must say, you really know a lot about Biology, are you a professor or teacher? If I asked you to descrive a cell membrane, would you just say a double layer of lipids containing proteins? I’m studying hard before exams.

    • #85982
      biofreakhazard
      Participant

      Hello,
      I would describe it (with specificity), an amphipathic phospholipid bilayer with molecules (mainly proteins) embedded within the lipids. And it is selectively permeable. Hope that helps.

    • #85991
      Yasaman.herandy
      Participant

      cell can only grow to a certain size, because if it grows more than that, then the surface hadn’t grown enough to be able to provide all the requirements of volume (Which has grown a lot)
      & I don’t believe that membrane strech when grow! it expands! the membrane is produced by rough & smooth endoplasmic reticulums.
      I said the membrane can grow to a certain size to be able to provide the volume; we know that enzymes need a surface for their function, so…!

    • #86132
      smellor
      Participant

      Well, the fact that the internal volume of a cell increases by the cube of the radius contributes to size limitations, since this is not in line with the increase in surface area, the larger the cell gets the more difficulty it will have obtaining enough nutrients. There are of course ways for cells to overcome this barrier, such as cytoplasmic streaming, infolding of the plasma membrane and the presence of vacuoles in the cell. The microvilli of the cells lining the gut is an example of a way to overcome this problem.

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