Cell Sizes Growth Limitations Volume Volume determines the

Cell Sizes & Growth Limitations

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

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 ODWS

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

How are surface area and volume affected by growth? Size / µm 1 2 3 4 5 6 Surface area / µm 2 6 24 54 96 150 216 Volume / µm 3 1 8 27 64 125 216 SA/V 6 3 2 1. 5 1. 2 1 © 2010 Paul Billiet ODWS

Comparing Surface Area and Volume changes © 2010 Paul Billiet ODWS

Surface Area: Volume Ratio © 2010 Paul Billiet ODWS

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 ODWS

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

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 •

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

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 8 X more nutrients and have 8 X more waste to get rid of ØFYI – If E. coli were left unreglated, it could engulf the Earth in one day because it doubles in volume every 30 minutes!!

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

DATA TABLE: Cell Size Comparison Cell 1 2 3 Dimensions (cm) Surface Area (cm 2) Volume (cm 3) Ratio Surface area to Volume

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