LIMITS TO SIZE

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

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

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

Comparing Surface Area and Volume changes © 2010 Paul Billiet ODWS

Surface Area:Volume Ratio © 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 Image Credits http://anatomia.uw.hu/ Chick blastodisc

Divide the cytoplasm into smaller volumes 8-cell Embryo Early human embryos Zygote 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