Cell Sizes & Cell Sizes & Growth Growth

LimitationsLimitations

Cell Size and LimitationsCell Size and Limitations

1. Diffusion limits size

2. DNA content limits size

3. Surface area to volume ratio limits size

Diffusion limits sizeDiffusion 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

DNA content limits sizeDNA 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.

Surface area to volume ratio Surface area to volume ratio limits sizelimits 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

FYIFYI – If E.coli were left unreglated, it could engulf the Earth in one day because it doubles in volume every 30 minutes!!

When do cells divide?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