#### Transcript limits to size

```TB p 93
WB p 153-154
LIMITS TO CELL
SIZE
WHY CANT WE HAVE
VERY LARGE CELLS ?
Cells need to constantly be exchanging
Materials through the cell membrane



enter
Food, oxygen, and water ______
cell membrane
through the _____________
wastes are removed through the
All _______
cell membrane
rate at which this _________
exchange
The ____
takes place ________
depends on the
___________
surface area of the cell
Cells need to constantly be exchanging
Materials through the cell membrane

food _______,
oxygen
The rate at which _____,
water are used and the amount
and ______
wastes produced also
of _______
larger
_________
increases as the cell gets ______

larger the cell becomes the
The ______
___________
less efficient it is at transporting
_________
materials through it’s cell
membrane
__________
Calculate
The left cube is 2cm x 2cm x 2cm
The right is 4 cubes each 1cm x 1cm x 1cm
For BOTH, work out the volume and the surface area
Now write a conclusion statement
Solution: Increase the ratio of
Surface Area to Volume in Cells



total area of
Surface area is the __________
the cell __________
membrane
Volume of the cell is the total
amount of stuff inside (_________
cytoplasm
_______
organelles
and __________)
Ratio of surface area to volume =
surface area ÷ volume
____________________
Ratio of Surface Area
to Volume in Cells
Cell Size
Surface Area (length x
width x 6)
Volume
(length x width x height)
Ratio of Surface Area to
Volume
What happens to surface area as cell gets bigger? It increases
If a cell gets too big

Volume of cell increases much
________
surface
____________
more rapidly than the ________
area so the surface area to
_____,
decreases and
volume ratio __________
membrane
transport through cell _________
________
inefficient
becomes _________
Cell Division


large cell
When one ______
smaller
divides into two ________
(daughter) cells
Solves the problems that
_______
occur when a cell gets
too big
_______
How are surface area and volume
affected by growth?
Size
/ µm
1
2
3
4
5
6
Surface
area
/ µm2
6
24
54
96
150
216
Volume
/ µm3
1
8
27
64
125
216
SA/V
6
3
2
1.5
1.2
1
Comparing Surface Area and
Volume changes
1000
900
800
700
600
Surface area
Volume
500
400
300
200
100
0
0
1
2
3
4
5
6
Size / µm
7
8
9
10
Surface Area:Volume Ratio
6
5
SA/V
4
3
2
1
0
0
1
2
3
4
5
6
Size / µm
7
8
9
10
What else could we do?



Good thing: Bigger cells have a
greater metabolism than smaller cells
BAD THING: bigger cells have a
proportionally less surface for
exchange
How to increase surface area with
increasing size?
Throw out extensions
Microvilli of
small
intestine
epithelium
Image Credit www.cytochemistry.net/
Multicellular organisms show

Mammals have a long
small intestine with
internal folding to absorb
digested food
Image Credit C. Candalh, INSERM
Multicellular organisms show