1. LIMITS TO SIZE
© 2016 Paul Billiet ODWS

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.
© 2016 Paul Billiet ODWS

3. Surface area
Surface area determines 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 inside bigger cells will be further from the surface of the cell.
© 2016 Paul Billiet ODWS

4. Growing cells
1µm
2µm
3µm
4µm
5µm
6µm
© 2016 Paul Billiet ODWS

5. 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
© 2016 Paul Billiet ODWS

6. Comparing Surface Area and Volume changes
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7. Surface Area:Volume Ratio
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8. 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 without increasing volume still further?
© 2016 Paul Billiet ODWS

9. Throw out extensions Microvilli of small intestine epithelium
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10. Flatten into a thin film
Chick blastodisc
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11. Divide the cytoplasm into smaller volumes
Zygote
8-cell Embryo
Early human embryos
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12. Multicellular organisms show the same adaptations
Flowering plants have an extensive, branched rooting system to absorb water and minerals
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13. Multicellular organisms show the same adaptations
Mammals have a long small intestine with internal folding to absorb digested food
C. Candalh, INSERM
© 2016 Paul Billiet ODWS