What is the connection between cells
and…
Desalination plant –Middle East
Converts salt water into fresh water
Snowboarding
parka shell and
snow pants
Dialysis machine
Draw a cross section of a “typical”
cell membrane.
What variables affect the passage of
molecules through cell membranes?
• Investigation introduction
Objectives
1. To observe the effects of distilled water and
salt solution on living plant and animal cells.
2. To investigate the influence of molecular size
and concentration on the passage of
molecules in and out of model cells.
3. To create a hypothesis to explain what you
observed.
Elodea and red blood cell observation
• Key question to consider:
• What happens to individual Elodea
and red blood cells when bathed in a
salt solution and in pure (distilled)
water?
• Make good observations
• Generate at least two alternative
hypotheses to explain your
observations for procedures 3 and 5:)
• Post the alternative hypothesis using
the Active Expressions (1 hypothesis
per responder)
Some chemistry terms used
• Solutions can be solids dissolved in liquids. They
could also be gases dissolved in liquids (such as
carbonated water).
• There can also be gases in other gases and liquids in
liquids. If you mix things up and they stay at an even
distribution, it is a solution.
• A simple solution is basically two substances that are
going to be combined. One of them is called the
solute. A solute is the substance to be dissolved
(sugar). The other is a solvent. The solvent is the
one doing the dissolving (water). As a rule of
thumb, there is usually more solvent than solute.
Homework
• Speculate on the possible effects of molecular
size and concentration on movement through
cell membranes. Using a model cell- design an
experiment or experiments to test your ideas.
Construct a pre-lab flowchart for your
experimental design.
Materials available for investigation
(found in lab packet)
•
•
•
•
Dialysis tubingRubber bands to tie off the ends of the dialysis tubing
Beakers
IKI solution (Lugol’s solution) to detect starch molecules. (demo
+/- test results)
• Glucose test strips- used to detect glucose molecules. (demo +/test results)
• Dropper bottles containing the following concentrations of
solutions:
– Distilled water (100% H20)
– 1% starch solution
– 5% starch solution
– 1.5% glucose solution
– 3% glucose solution
– Quadruple beam balances
Day 2• After your pre-lab flowchart has been stamped off for
completion, decide as a group the different
experiments that you will run to test your hypotheses.
• Professional points will be lost for groups who do not
clean up their stations
• Record all of your results. Graph your quantitative
data and be ready to present your findings to the class
in 30 minutes.
• Did the class results reveal a consistent pattern? If
so, what was it?
• Which of the proposed hypotheses were supported by
the experimental findings? Explain
• Homework   complete question 11
Day 3
• Draw a cross section of your model cell
membrane. Label your diagram.
What effect does molecular size and
concentration have on movement
through cell membranes?
solution, hypertonic,
n a mixture containing a concentration of solute in excess of the concentration of the
same solute in another mixture to which it is compared. When the two solutions are
placed on opposite sides of a permeable membrane (either artificial or natural, as with
cell membranes), the hypertonic solution attracts the solvent from the hypotonic solution,
equalizing the concentration of the solute in both. See also solution, hypotonic; solution,
isotonic; and osmosis.
solution, hypotonic,
n a mixture containing a concentration of solute that is lower than the concentration of
the same solute in another mixture to which it is compared. When two such solutions are
separated by a permeable membrane, the solvent of the hypotonic solution flows
through the membrane to the hypertonic solution, equalizing the concentration of the
solute in both. See also solution, hypertonic; solution, isotonic; and osmosis.
solution, isotonic,
n a mixture containing the same concentration of solute as another mixture to which it is
compared. When separated by a permeable membrane, osmosis does not occur. See
also solution, hypertonic; solution, hypotonic; and osmosis.
What causes molecules to pass in
and out of cells?
How would you now explain what happened
to the plant and animal cells when placed in
salt water and distilled water?
Application: what are some practical applications of semi
permeable membranes?- Write a one page synopsis of how these
technologies work. Or write a one page summary of what the
process of salinization is, how it is caused by humans and how
this process can impact living organisms.
http://science.howstuffworks.com/reverse-osmosis.htm