Cell
Size
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As the cell grows larger the cells DNA
will no longer be able to serve the
increasing needs of the growing cell.
The larger the cell the more trouble it
has moving nutrients such as food,
oxygen and water and wastes across the
cell membrane.
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As the cell increases in size it does not
make an extra copy of DNA so the DNA
that it has will no longer be able to meet
the needs of the growing cell.
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The rate at which the nutrients and
wastes are exchanged depends on the
surface area of a cell.
Surface Area (SA)= 6 x heigth x width
The rate at which nutrients are used up
and waste products are produced
depends on the cells volume.
Volume (V)= length x width x height
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There is a relationship between a
cells volume and its surface area and
why a cell must divide as they grow
As a cell increases in size, its volume
increases faster than its surface area
Ideally, a cell wants to have a large
surface area with a small volume or a
large SA/V ratio
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Find the SA/V ratio of a 4cm x 4 cm x 4
cm cube.
SA = 6 x 4 x 4 = 96
V = 4 x 4 x 4 = 64
SA/V = 96/64
SA/V=48/32
SA/V=24/16
SA/V=12/8
SA/V=6/4
SA/V= 3/2
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Find the surface area/volume ratio of a 1
cm x 1cm x 1 cm cube.
SA for a cube = 6 x height x width
V = height x width x length
SA/V = 6 x 1 x 1/1 x 1 x 1 = 6/1
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Now find the SA/V ratio of a 2x2x2 cm
cube.
SA= 6x2x2
V=2x2x2
SA/V=24/8
SA/V=12/4
SA/V=6/2
SA/V=3/1
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Now find the SA/V ratio of a 3x3x3 cm
cube.
SA= 6x3x3=54
V= 3x3x3=27
SA/V=54/27
SA/V=18/9
SA/V=6/3
SA/V=2/1
6/1
3/1
2/1
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Cell division-the splitting of a single cell
into 2 daughter cells
A cell must divide when:
1. A cell has grown so that the nucleus
can no longer control all of the
cytoplasm
2. The SA/V ratio is too low
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Growth- Increase in size
Repair- Accomplished by cell
regeneration at the site of injury
Reproduction- Either asexually
(requires one parent) or sexually
(requires two parents)
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