LIMITS TO SIZE
Volume




Volume determines the amount
metabolism in the cytoplasm
Metabolism will require import of
precursors
Metabolism will result in the export
of secretions
And the export of excretory
products
© 2010 Paul Billiet ODWS
Surface area




Surface area will determine the exchange
of materials between the cell and its
environment
Bigger cells will metabolise more
But they will need more surface to support
that metabolism
And the sites of metabolism in bigger cells
will be further from the surface of the cell
© 2010 Paul Billiet ODWS
Growing cells
1µm
2µm
3µm
4µm
5µm
6µm
© 2010 Paul Billiet ODWS
How are surface area and volume
affected by growth?
Size
/ µm
1
2
3
4
5
6
Surface
area
/ µm2
6
24
54
96
150
216
Volume
/ µm3
1
8
27
64
125
216
SA/V
6
3
2
1.5
1.2
1
© 2010 Paul Billiet ODWS
Comparing Surface Area and
Volume changes
1000
900
800
700
600
Surface area
Volume
500
400
300
200
100
0
0
1
2
3
4
5
6
Size / µm
© 2010 Paul Billiet ODWS
7
8
9
10
Surface Area:Volume Ratio
6
5
SA/V
4
3
2
1
0
0
1
2
3
4
5
6
Size / µm
© 2010 Paul Billiet ODWS
7
8
9
10
Solving the problem



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?
© 2010 Paul Billiet ODWS
Throw out extensions
Microvilli of
small
intestine
epithelium
Image Credit www.cytochemistry.net/
Flatten into a thin film
Image Credits http://anatomia.uw.hu/
Chick blastodisc
Divide the cytoplasm into
smaller volumes
8-cell Embryo
Early human
embryos
Zygote
Image Credit http://www.advancedfertility.com/
Image Credit http://www.rmfcfertility.com/
Multicellular organisms show
the same adaptations

Flowering plants have an extensive, branched
rooting system to absorb water and minerals
Image Credit http://ecomerge.blogspot.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