LIMITS TO SIZE

DO NOW: 3/16/16 1. What do animals need to gain from their environment to stay alive? How do these substances get to cells? 2. What do plants need to gain from their environment to stay alive? How do these substances get to cells? 3. Give 2 examples of wastes that living organisms have to get rid of somehow. How does the waste get from the cells to where it is excreted?

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 metabolize 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? SA/V Volume / µm3 Surface area / µm2 Size / µm 1 2 3 4 5 6 6 24 54 96 150 216 1 8 27 64 125 216 6 3 2 1.5 1.2 1 © 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 Challenge to cells: 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

Examples of Exchange/ Absorption Surfaces Alveoli, exchange of oxygen and carbon dioxide Small intestine, absorption of nutrients Liver cells (hepatocytes), absorption of metabolically active substances, blood sugar levels adjusted Root hairs, water and minerals absorbed Fungal hyphae, absorption of nutrients

Think Tank Questions: Increasing Size and Complexity Single celled organisms do not need complex exchange and transport systems. Why not? How does exchange of substances take place? How do they transport substances into the center? Bigger organisms with several or many layers of cells and which are more active need specialized exchange and transport systems. Why?