Diffusion
RS: Ms. Alvarez
CT:Mrs. Rojas
Adapted from C. Goedhart
Stinkbombs
Why does the smell of a
stinkbomb travel?
Why does the smell
eventually disappear?
Why do smells linger
longer in a small room
than in a large room?
Diffusion
• Molecules move from an area where there are
many to an area where there are few.
– This is called moving down a concentration gradient.
• Molecules move until they are evenly
distributed.
– Even distribution is called equilibrium.
• Molecules can diffuse in a liquid or in a gas.
Solutions
• A solution is a mixture of two or
more substances.
• Solute: a substance (like salt) that
breaks up in a solvent (like water).
• Solvent: a liquid with the power to
break apart (dissolve) substances.
Solute size
• If there are no barriers, a
solute of any size eventually
reaches equilibrium (or even
distribution) in the solvent.
• Cell membranes let small
solutes in and out through
diffusion.
• Larger solutes (or molecules)
can’t diffuse into the cell, and
enter through special
proteins or vesicles.
Osmosis
• Osmosis is a kind of
diffusion that refers to
the movement of water.
• Water likes to move from
an area where there are
few solutes to an area of
many solutes.
• In other words, water
likes to dilute things.
• Water molecules pass
easily through
membranes.
Osmosis words
• HYPERTONIC
– a solution has more solutes, or is more
concentrated than another.
• HYPOTONIC
– a solution has fewer solutes, or is more dilute
than another.
• ISOTONIC
– a solution has equal concentration to another.
Smelly Balloons
 Like the plasma membrane, the balloon
is a SEMIPERMEABLE MEMBRANE.
 Semipermeable means that the membrane allows
movement of certain molecules across.
 Molecules small enough to fit through the pores
in the balloon will move by DIFFUSION
 Both in and out of the balloon.
 The food extract smell molecules are small
enough to diffuse through the membrane.
 Eventually, the diffusing molecules reach the
smell receptors in your nose.
Smelly Balloons
• Each group will get 1 balloon initially.
After 3 minutes you will rotate
balloons. This will continue until all
five balloons have been rotated.
• Fill in balloon number, scent
description, and strength of scent
(none, weak, strong) in chart for all
5 balloons
Balloon
number
Smell
Description
Smell
Strength
(None,Weak,
Strong)
1
2
3
4
5
Questions
1.
2.
3.
How do the smell molecules get out of the balloon?
This process by which molecules move from a place of
higher concentration (inside the balloon) to a place of
lower concentration (outside the balloon) is called
State two ways the latex skin of a balloon is like a cell
membrane.
A.
B.
4. What is diffusion?
5. How do molecules move?
6. What is solute?
7. What is a solvent?
8. What is osmosis?
9. A. Which was the independent variable?
B. Which was the dependant variable?
C. Which was the control?