1. Cell Sizes & Growth Limitations

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. EQ: What factors controls or limit the Cell Size? 1. Diffusion limits size 2. DNA content limits size 3. Surface area to volume ratio limits size

10. How does Diffusion limit cell size? An oxygen molecule follows a path to the mitochondria (Oxygen)… plasma membrane  cytoplasm  mitochondria Smaller size allows the cell to be more efficient

11. EQ: How does DNA content limits size? Cells usually contain only one nucleus DNA is found in the nucleus DNA makes RNA RNA will travel through the cytoplasm to the ribosomes RNA assists the ribosomes in making proteins DNA is responsible for the whole above process If the cell was very large, there would not be enough DNA to support the cell.

12. EQ: How does Surface area to volume ratio limits cell size As a cell increases, it volume increases much faster than its surface area If a cell doubled, the cell would require 8X more nutrients and have 8X more waste to get rid of  FYI  FYI – If E.coli were left unreglated, it could engulf the Earth in one day because it doubles in volume every 30 minutes!!

13. EQ: When do cells divide? All organisms grow and change. Cells are constantly growing, dividing, and dying Some cells divide more than others – Heart & nerve system cells rarely (if ever) divide Skin cells, on the other hand, are constantly dividing Growth is related to cell specificity and activity If cell growth is uncontrolled – leads to cancer