Post on 28-Mar-2015
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?
11.21.5236
216125642781
2161509654246
654321
SA/V
Volume / µm3
Surface area / µm2
Size / µm
© 2010 Paul Billiet ODWS
Comparing Surface Area and Volume changes
0
100
200
300
400
500
600
700
800
900
1000
0 1 2 3 4 5 6 7 8 9 10
Size / µm
Surface areaVolume
© 2010 Paul Billiet ODWS
Surface Area:Volume Ratio
0
1
2
3
4
5
6
0 1 2 3 4 5 6 7 8 9 10
Size / µm
SA
/V
© 2010 Paul Billiet ODWS
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
Chick blastodisc
Image Credits http://anatomia.uw.hu/
Divide the cytoplasm into smaller volumes
Early human embryos
Zygote
8-cell Embryo
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