Date post: | 02-Jan-2016 |
Category: |
Documents |
Upload: | martina-perkins |
View: | 221 times |
Download: | 0 times |
LIMITS TO SIZE: Why are Cells Small Lab?
Why are cells so small?
The answer to this question has as much to do with mathematics as biology. Imagine a cell that is shaped like a cube. As the cell increases, its surface area to volume ratio changes.
Surface area Surface area is the total area of the
outside surface. For cubes it is expressed in squared units (such as cm2 or m2).
The S.A. of a cell will determine the amount of materials that can be exchanged between the cell and its environment.
Equation: SA = length x width x # of sides
© 2010 Paul Billiet ODWS
Volume Volume is the amount of space
something occupies. It is expressed in cubic units (such as cm3 or m3).
The volume of a cell will determine the amount of chemical reactions or the metabolism of the cell.
Equation: V= length x width x height
© 2010 Paul Billiet ODWS
Surface Area to Volume Ratio
Surface Area to Volume Ratio is the comparison of the amount of surface area (what is on the outside) to the volume (what is on the inside)
Cells need to have a large surface area to its volume (hence a high S.A. to V ratio) because wastes need to be able to exit, and nutrients need to be able to enter the cell quickly.
Growing cells
1cm
2cm
3cm
4cm
5cm
6cm© 2010 Paul Billiet ODWS
How are surface area and volume affected by growth?
1:11.2:11.5:12:13:16:1
216125642781
2161509654246
654321
SA/V
Volume (cm3)
Surface area (cm2)
Length of side (cm)
© 2010 Paul Billiet ODWS
Comparing Surface Area and Volume changes
0
100
200
300
400
500
600
700
800
900
1000
0 1 2 3 4 5 6 7 8 9 10
Size / µm
Surface areaVolume
© 2010 Paul Billiet ODWS
(cm)
Surface Area:Volume Ratio
0
1
2
3
4
5
6
0 1 2 3 4 5 6 7 8 9 10
Size / µm
SA
/V
© 2010 Paul Billiet ODWS
(cm)
As cells get larger, the S.A.:V gets __________________.smaller
Since transport of materials in and out of the cell can only happen at the cell’s surface, what problem does this pose?
Bigger cells have a greater volume (meaning a greater metabolism) than smaller cells
BUT bigger cells have a proportionally less surface for exchange.
Diffusion can’t take place as quickly!© 2010 Paul Billiet ODWS
1. Throw out extensions
Microvilli of small intestine epithelium
Image Credit www.cytochemistry.net/
What are ways to increase surface area while increasing size.
2. Flatten into a thin film
Chick blastodisc
Image Credits http://anatomia.uw.hu/
3. Or just divide the cytoplasm into smaller volumes
Early human embryos
Zygote
8-cell Embryo
Image Credit http://www.advancedfertility.com/ Image Credit http://www.rmfcfertility.com/
Do larger organisms have larger cells or more cells than smaller organisms?
More Cells!!!!
Multicellular organisms show the same adaptations
Flowering plants have an extensive, branched rooting system to absorb water and minerals
Image Credit http://ecomerge.blogspot.com
Multicellular organisms show the same adaptations
Mammals have a long small intestine with internal folding to absorb digested food
Image Credit C. Candalh, INSERM