Download factors affecting the rate of diffusion - Mr. Lesiuk

FACTORS AFFECTING THE RATE OF
DIFFUSION
I) Surface Area vs. Volume
- Cells are limited in their size because they
must maintain a high “Surface Area :
Volume” ratio.
- Nutrients (oxygen and glucose) must enter a
cell while wastes (carbon dioxide and urea)
must exit a cell through the cell membrane.
- The amount of cell membrane = Surface
Area of the cell.
- Inside the cell, organelles use up nutrients
and produce wastes. The larger the cell, the
more nutrients needed and the more wastes
produced.
- The size of the cell (based on the number of
organelles) = Volume of the cell.
Cell
S.A
LxWx6
Volume
LxWxH
S.A. : Volume
Ratio
A
6 units2
1 unit3
6:1
B
24 units2
8 units3
3:1
C
96 units2
64 units3
1.5 : 1
D
384 units2
512 units3
0.75 : 1
- Small cells have a high “SA:Volume” ratio, they
can supply the organelles with plenty of nutrients
and rapidly remove wastes.
- Large cells have a low “SA:Volume” ratio
because volume rises faster than surface area. If a
cell gets too big, wastes will build up and nutrients
will run out; cell cannot survive.
- Therefore, cells are limited in their size. The
more active a cell is, the smaller it must be. Active
cells need more nutrients and they produce more
wastes.
- How do cells occupy the large volumes associated
with large organisms?
The cells reproduce frequently through mitosis to
maintain their small size (high “SA:Volume”
ratios) while creating millions of cells to fill these
larger volumes.
(As opposed to using fewer larger cells)
- Some cells can achieve a large size while still
maintaining a high SA:Volume ratio. This is
achieved by producing folds of the cell membrane
(microvilli) to increase SA.
- These folds allow the cell to gain more
surface area without a large increase in
volume.
Checkout :
http://www.hillstrath.on.ca/moffatt/bio3a/cellbio/sa-vsoln.htm
II) FACTORS THAT WILL AFFECT THE RATE
OF DIFFUSION
1. Concentration gradient:
– the difference in concentration between two
areas.
-- the greater the [ ] gradient, the faster the
diffusion.
Higher
Concentration
Lower
Concentration
2. The size and shape of the molecules:
- Smaller molecules that fit through pores will
pass at a faster rate.
3. Temperature:
– Warmer = faster (more kinetic energy in
the particles)
http://mutuslab.cs.uwindsor.ca/schurko/animation
s/waterphases/status_water.htm
Click on the first button
4. Type of medium:
– Diffusion is faster in gases than in liquids
(more empty space between the molecules of a
gas as well as greater Kinetic E)
5. Movement of the medium
–Water or air currents speed up diffusion.
Example: Stirring or heating can create
currents (promotes mixing).