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Do cells grow larger to increase
the overall size of an
organism????
Regents Biology
Biology is the only subject in
which multiplication is the same
thing as division…
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2006-2007
MITOSIS:
Making New Cells
Making New DNA
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Where it all began…
We all start as a cell smaller than
a period at the end of a sentence…
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And now look what can happen…
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How did you
get from there
to here?
Getting from there to here…
 Going from egg to baby….
the original fertilized egg has to divide…
and divide…
and divide…
and divide…
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Limits to Cell Growth
? Do cells grow larger to increase an organism’s size?
NO!!
Why?
1) DNA
- cell parts rely on DNA for instructions
- increase in size = more parts needing info
* DNA has a limit on ability to send out
instructions
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2) Movement of Materials
- increase in size = larger volume (inner space)
less surface area (cell membrane)
Therefore:
- materials get crowded moving in/out of cell
Example:
1cm x 1cm cell
3cm x 3cm cell
Surface Area =
1cm x 1cm x 6 sides
= 6 cm2
3cm x 3cm x 6
= 54 cm2
Volume =
1cm x 1cm x 1cm
= 1cm3
Ratio =
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6 to 1
3cm x 3cm x 3cm
= 27 cm3
2 to 1
Solution
- Cell division increases the number of cells
which increases the organism’s size.
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Why else do cells divide…
 One-celled organisms
1.
2.
for reproduction
asexual reproduction (clones)
amoeba
 Multi-celled organisms
1.
for growth & development

2.
from fertilized egg to adult
for repair & replacement

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replace cells that die from
normal wear & tear or from injury
starfish
Dividing cells…
 What has to be copied
DNA
 organelles
 cell membrane
 lots of other
molecules

 enzymes
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plant cell
animal cell
Genetic Material Involved
1) Chromatin
- thin strands of DNA
that can form into
chromosomes.
2) Chromosomes
- thick rod shaped
structures that
carry DNA to new
cells.
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double-stranded
human chromosomes
ready for mitosis
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Chromosomes of Human Female
46 chromosomes
23 pairs
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Chromosomes of Human Male
46 chromosomes
23 pairs
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Cell Cycle: Life Cycle of Cells
 Stage 1: cell copies DNA
DNA
cell
nucleus
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interphase
Cell Cycle
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Mitosis: Dividing DNA & cells
 Stage 2: DNA winds up into chromosomes

DNA is wound up into chromosomes to keep it
organized
duplicated chromosomes
(prophase)
cell
nucleus
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Mitosis: Dividing DNA & cells
 Stage 3: Chromosomes line up
chromosomes line up in middle
 attached to protein “cables” that will
help them move

metaphase
duplicated chromosomes
lined up in middle of cell
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Mitosis: Dividing DNA & cells
 Stage 4: Chromosomes separate
chromosomes split, separating pairs
 start moving to opposite ends

anaphase
chromosomes split &
move to opposite ends
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Mitosis: Dividing DNA & cells
 Stage 5: Cell starts to divide
cells start to divide
 nucleus forms again

Telophase
- animals- cell pinches in
- plants- cell plate forms
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Mitosis: Dividing DNA & cells
 Stage 6: DNA unwinds again
cells separate
 now they can do their every day jobs

cytokinesis
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New “daughter” cells
 Get 2 exact copies of original cells
same DNA
 “clones”

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Cell division in Animals
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Mitosis in whitefish embryo
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Mitosis in plant cell
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onion root tip
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Overview of mitosis
interphase
I.P.M.A.T.C.
prophase
Please Make Another Two Cells
cytokinesis
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metaphase
anaphase
telophase