12/2/2016
Why Are Cells So Small?
The Importance of Cell Size
• Cells need sufficient surface area to allow
adequate transport of nutrients in and wastes
out.
• As cell volume increases, so does the need for
the transporting of nutrients and wastes.
Why Are Cells So Small?
Comparing Surface Area and Volume
changes
• However, as cell volume increases the surface
area of the cell does not expand as quickly.
– If the cell’s volume gets too large it cannot
transport enough wastes out or nutrients in.
• Thus, surface area limits cell volume/size.
1000
900
800
700
600
Surface area
Volume
500
400
300
200
100
0
0
1
2
3
4
5
6
7
8
9
10
Size / µm
© 2010 Paul Billiet ODWS
Surface Area:Volume Ratio
Natural laws limit cell size.
• ratio of cell surface area to cell volume sets
upper limits on cell size
6
5
SA/V
4
3
2
1
0
0
1
2
3
4
5
6
7
8
9
10
Size / µm
© 2010 Paul Billiet ODWS
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12/2/2016
Solving the problem
Throw out extensions
• Bigger cells have a greater
metabolism than smaller cells
• BUT bigger cells have a
proportionally less surface for
exchange
• How to increase surface area with
increasing size?
Microvilli of
small
intestine
epithelium
Image Credit www.cytochemistry.net/
© 2010 Paul Billiet ODWS
Flatten into a thin film
Divide the cytoplasm into smaller
volumes
8-cell Embryo
Early human
embryos
Image Credits http://anatomia.uw.hu/
Chick blastodisc
Zygote
Image Credit http://www.advancedfertility.com/
Multicellular organisms show the same
adaptations
• Flowering plants have an extensive, branched
rooting system to absorb water and minerals
Image Credit http://www.rmfcfertility.com/
Multicellular organisms show the same
adaptations
• Mammals have a long
small intestine with
internal folding to absorb
digested food
Image Credit C. Candalh, INSERM
Image Credit
http://ecomerge.blogspot.c
om
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