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]