Download - 2.1.4: Relative sizes
2.1.4: Relative sizes
CONVERTING UNITS
mm
µm
nm
x 1,000
x 1,000
÷ 1,000
÷ 1,000
Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit.
1nm
A molecule
http://mendosa.com/glucose_molecule.jpg
10nmA molecule
http://www.biolibogy.com/images/structure_of_plasma_membrane.JPG
Glucose (1nm)
A virus – the T bacteriophage
http://oceanworld.tamu.edu/resources/oceanography-book/Images/BacteriophageCartoon.jpg
10nm
100nm
E.coli (bacteria cell)Bacteriophage (virus)
100nm0.1µm
1000nm1µm
http://bio1903.nicerweb.com/doc/class/bio1903/Locked/media/ch18/18_01T4PhageEColi_LP.jpg
http://www.cic-caracas.org/departments/science/images/08eukaryote.jpg
Bacteria (1µm) Organelle (10µm)
Cell ( up to 100µm)
1 nm molecules 10 nm membrane thickness 100 nm virus
1 µm bacteria(up to) 10 µm organelles(up to) 100 µm cells
1mm = 1,000 µm 1 µm = ___1 mm 1,000
1 µm = 1,000 nm 1 nm = ___1 µm 1,000
MollyMetVirgil
ButOrganisedCells
IB Question: State the typical size of (i) a bacterium [1] (ii) An average eukaryotic cell [1]
(i) (approximately) 1μm [1]Accept any value between .5μm and 1.0μm.
(ii) (approximately) 10μmto 100μm [1]Accept any value within this range.
2.1.5: Scale bar
15 µm
2.1.6: Surface area : volume
2.1.6: Surface area : volumeLets look at Surface areas and volumes………
• Fill in the table below:
a
a
a Size of side (a)
Surface area of the box (a x a x 6)
Volume of the box(a x a x a)
Surface area to volume ratio
1 6 1 6 : 1
2
3
4
5
6
7
Size of side (a)
Surface area of the box (a x a x 6)
Volume of the box(a x a x a)
Surface area to volume ratio
1 6 1 6 : 1
2 24 8
3 54 27
4 96 64
5 150 125
6 216 216
7 294 343
Size of side (a)
Surface area of the box (a x a x 6)
Volume of the box(a x a x a)
Surface area to volume ratio
1
2
3
4
5
6
7
2.1.6: Surface area:volume
IB Question: Explain the importance of the surface area to volume ratio as a factor limiting cell size. [7]
as size increases both surface area and volume increase, but volume increasesmore / ratio of surface area to volume decreases as size of cell increases;rate of metabolism is a function of its mass to volume ratio;surface area limits/affects the rate at which substances can enter (or leave) thecell;volume determines the rate at which material is produced/used;oxygen/nutrients/substances will take too long to diffuse into/out of the centre ofthe cell if it is too big;excretory products would take too long to be eliminated;heat will take too long to be eliminated;example of cell adaptation to increase the ratio of surface area:volume e.g. roothair cell; [7 max]