1. Cell Sizes & Growth Limitations

2. Cell Size and Limitations
1. Diffusion limits size
2. DNA content limits size
3. Surface area to volume ratio limits size

3. Diffusion limits size
An oxygen molecule follows a path to the mitochondria
(Oxygen)…
plasma membrane  cytoplasm  mitochondria
Because of the small size of the cell, oxygen molecules take a fraction of a second to reach the mitochondria.
Smaller size allows the cell to be more efficient

4. 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.

5. Surface area to volume ratio limits 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 – If E.coli were left unreglated, it could engulf the Earth in one day because it doubles in volume every 30 minutes!!

6. 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