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