1. LIMITS TO SIZE

2. 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?

3. 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

4. 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

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

6. 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

7. Surface Area:Volume Ratio
© 2010 Paul Billiet ODWS

8. 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

9. Throw out extensions Microvilli of small intestine epithelium
Image Credit

10. Flatten into a thin film
Image Credits
Chick blastodisc

11. Divide the cytoplasm into smaller volumes
8-cell Embryo
Early human embryos
Zygote
Image Credit
Image Credit

12. Multicellular organisms show the same adaptations
Flowering plants have an extensive, branched rooting system to absorb water and minerals
Image Credit

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

14. 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

15. 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?