LIMITS TO SIZE

© 2007 Paul Billiet ODWS

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© 2007 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

© 2007 Paul Billiet ODWS

Growing cells

1µm

2µm

3µm

4µm

5µm

6µm© 2007 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

© 2007 Paul Billiet ODWS

Comparing Surface Area and Volume changes

0100200300400500600700800900

1000

0 1 2 3 4 5 6 7 8 9 10Size / µm

Surface areaVolume

© 2007 Paul Billiet ODWS

Surface Area:Volume Ratio

0

1

2

3

4

5

6

0 1 2 3 4 5 6 7 8 9 10Size / µm

SA/V

© 2007 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?

© 2007 Paul Billiet ODWS

Throw out extensions

Microvilli of small intestine epithelium

© copyright 2001 Gwen V. Childs, Ph.D., University of Arkansas for Medical Sciences

Flatten into a thin film

Chick blastodisc© Developmental Biology Online © Developmental Biology Online

Divide the cytoplasm into smaller volumes

Early human embryos

Zygote

8-cell Embryo

© Reproductive Medicine and Fertility Center

Multicellular organisms show the same adaptations

Flowering plants have an extensive, branched rooting system to absorb water and minerals

© Illinois Enviromental Protection Agency© Text 2007 Paul Billiet ODWS

Multicellular organisms show the same adaptations

Mammals have a long small intestine with internal folding to absorb digested food

lithograph plate 20th U.S. edition of Gray's Anatomy of the Human Body, originally published in 1918. This image is in the public domain because its copyright has expired

© Text 2007 Paul Billiet ODWS