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Cell Growth Cell Growth

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					          Cell Growth

“All living things grow and develop”
           Cell Size Limitations
1. Over burdened DNA
     1. DNA = nucleic acid that provides instructions to
        ribosomes to produce protein
     2. DNA controls activities of the cell within the nucleus
2. Surface area to volume ratio
    1.   Surface area increases slowly
    2.   Volume increases quickly
3. Just can’t get enough or get rid of enough
     1. Cell membrane is site of material exchange
     2. Diffusion, facilitated diffusion, osmosis too slow
           DNA Overload
• There’s too much work!!!
• Not enough information to go around in
  the cell
• As a cell grows, it has more organelles
  and conducts more activities
• Cellular activities require enzymes
• Enzymes are proteins; therefore, must be
  produced through protein synthesis
• Protein synthesis requires information
  from DNA
      Just Can’t Get Enough
• Can’t get enough oxygen, food and
  water across the cell membrane to
  supply the cell
• Can’t get rid of waste products quickly
  enough to prevent self poisoning
• Process of diffusion/osmosis is too
  slow
 Surface Area to Volume Ratio
• The surface area increases slower than
  the volume . . . OR . . .
• The volume increases faster than the
  surface area!!
• Therefore, the surface area to volume ratio
  decreases!!
• More volume = more demands because
  the rate of consumption increases
• Surface area can’t keep up with demands
Surface Area
             Surface Area vs. Volume




                                                                                          Surface area = 96 mm2
                                                                                          Volume = 64 mm3

Surface area to volume ratio:   Surface area to volume ratio:   Surface area to volume ratio:
6:1 or 6/1 = 6                  24:8 or 24/8 = 3                96:64 or 96/64 = 1.5



As a cell grows, notice the value of the surface area to volume ratio!

It decreases!
             So . . .
   What can cells do about that?
• Cell division – the process used by cells
  to divide

• Dividing rectifies the problem of putting too
  much demand on DNA
• Dividing increases the surface area to
  volume ratio
• Dividing reduces the size of the cell making it
  possible to distribute nutrients and remove
  waste!
               Replication
• DNA makes copies of itself
• Review:
  – DNA unzips
  – Complementary nucleotides attach
  – Two new strands of identical DNA are produced
  – Each new strand has one strand from the
    original
• DNA must be copied so that each new cell
  has a complete set of DNA of the original
              Reproduction
• Reproduction is the production of offspring
  or a new organism
• There are two general methods/strategies
  of reproduction:
  – Asexual reproduction – production of
    offspring that requires only one parent
  – Sexual reproduction – production of
    offspring that requires the combination of two
    different cells
         Asexual Reproduction
• Organisms produce offspring through one
  parent
• Offspring have the same genetic information
  (information for making proteins) as the parent
• They are, in essence, clones!!!
• Unicellular organisms, like bacteria, usually
  reproduce asexually
• Some multicellular organisms reproduce
  asexually
     Asexual Reproduction &
     Multicellular Organisms
• Organisms such as plants and protists can
  reproduce asexually
• Hydra reproduce through budding!
• Plants can reproduce asexually
  – Bulbs
  – Cuttings
  – Rhizomes
  – Roots/shoots/runners
Budding in Hydra
Binary Fission of Amoeba
Runners of Strawberry Plants
Asexual Reproduction in Plants
Asexual Reproduction = Clones
        Sexual Reproduction
• Sexual reproduction is a process where
  two cells (gametes) from different parents
  join together to form a new organism
• Offspring of sexual reproduction have
  different genetic information from both
  parents
• Most plants and animals and some
  unicellular organisms reproduce sexually
Sexual Reproduction
Asexual vs. Sexual Reproduction
        Asexual                    Sexual
• No need to find mate;   • Must find a mate;
  therefore, quicker        therefore, slower
• No genetic diversity;   • Genetically diverse;
  therefore, vulnerable     therefore, healthy

				
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posted:11/21/2011
language:English
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