1. LIMITS TO SIZE

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 © 2010 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 © 2010 Paul Billiet ODWSODWS

4. Growing cells 1µm 2µm 3µm 4µm 5µm 6µm © 2010 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 © 2010 Paul Billiet ODWSODWS

6. Comparing Surface Area and Volume changes © 2010 Paul Billiet ODWSODWS

7. Surface Area:Volume Ratio © 2010 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? © 2010 Paul Billiet ODWSODWS

9. Throw out extensions Microvilli of small intestine epithelium Image Credit www.cytochemistry.net/www.cytochemistry.net

10. Flatten into a thin film Chick blastodisc Image Credits http://anatomia.uw.hu/http://anatomia.uw.hu/

11. Divide the cytoplasm into smaller volumes Early human embryos Zygote 8-cell Embryo Image Credit http://www.advancedfertility.com/http://www.advancedfertility.com/ Image Credit http://www.rmfcfertility.com/http://www.rmfcfertility.com

12. Multicellular organisms show the same adaptations Flowering plants have an extensive, branched rooting system to absorb water and minerals Image Credit http://ecomerge.blogspot.comhttp://ecomerge.blogspot.com

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