1. LIMITS TO SIZE

2. Volume: The space inside the cell
Volume determines the amount metabolism in the cytoplasm
Metabolism will require import of supplies
Metabolism will result in the export of waste and product
© 2010 Paul Billiet ODWS

3. Surface area: the outside barrier of the cell (membrane)
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

4. Growing cells Cell Size Surface Area (length x width x 6) Volume
(length x width x height)
Ratio of Surface Area to Volume

5. Comparing Surface Area and Volume changes
© 2010 Paul Billiet ODWS

6. Surface Area:Volume Ratio
© 2010 Paul Billiet ODWS

7. 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

8. Throw out extensions Microvilli of small intestine epithelium
Image Credit

9. Flatten into a thin film
Image Credits
Chick blastodisc

10. Divide the cytoplasm into smaller volumes
8-cell Embryo
Early human embryos
Zygote
Image Credit
Image Credit

11. Multicellular organisms show the same adaptations
Flowering plants have an extensive, branched rooting system to absorb water and minerals
Image Credit

12. Multicellular organisms show the same adaptations
Mammals have a long small intestine with internal folding to absorb digested food
Image Credit C. Candalh, INSERM