1. LIMITS TO SIZE © 2007 Paul Billiet ODWSODWS

2. 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 ODWSODWS

3. 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 ODWSODWS

4. Growing cells 1µm 2µm 3µm 4µm 5µm 6µm © 2007 Paul Billiet ODWSODWS

5. How are surface area and volume affected by growth? 11.21.5236 216125642781 2161509654246 654321 SA/V Volume / µm 3 Surface area / µm 2 Size / µm © 2007 Paul Billiet ODWSODWS

6. Comparing Surface Area and Volume changes © 2007 Paul Billiet ODWSODWS

7. Surface Area:Volume Ratio © 2007 Paul Billiet ODWSODWS

8. 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 ODWSODWS

9. Throw out extensions Microvilli of small intestine epithelium © copyright 2001 Gwen V. Childs, Ph.D., University of Arkansas for Medical Sciences

10. Flatten into a thin film Chick blastodisc © Developmental Biology OnlineDevelopmental Biology Online © Developmental Biology OnlineDevelopmental Biology Online

11. Divide the cytoplasm into smaller volumes Early human embryos Zygote 8-cell Embryo © Reproductive Medicine and Fertility Center

12. Multicellular organisms show the same adaptations Flowering plants have an extensive, branched rooting system to absorb water and minerals © Illinois Enviromental Protection AgencyIllinois Enviromental Protection Agency © Text 2007 Paul Billiet ODWSODWS

13. 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 ODWSODWS