Cell Sizes & Cell Sizes & Growth Growth

LimitationsLimitations

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?

11.21.5236

216125642781

2161509654246

654321

SA/V

Volume / µm3

Surface area / µm2

Size / µm

© 2010 Paul Billiet ODWS

Comparing Surface Area and Volume changes

0

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1000

0 1 2 3 4 5 6 7 8 9 10

Size / µm

Surface areaVolume

© 2010 Paul Billiet ODWS

Surface Area:Volume Ratio

0

1

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0 1 2 3 4 5 6 7 8 9 10

Size / µm

SA

/V

© 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 EQ: What factors controls or limit the Cell Size?the Cell Size?

1. Diffusion limits size2. DNA content limits size3. Surface area to volume ratio limits size

How does Diffusion limit How does Diffusion limit cell size?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 EQ: How does DNA content limits size?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.

EQ: How does Surface area to EQ: How does Surface area to volume ratio limits cell sizevolume 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 ofFYIFYI – 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?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