Name________________________________________
Date_______
Over the years, scientists have collected the following data about cell membranes (listed in
chronological order).
Lipid soluble substances enter cells faster than water soluble substances (lipids are nonpolar).
Lipids are unstable in water because they repel water (think of oil in water).
o If you don't have a mental picture, take some drops of oil and put them in a glass of
water at home and see for yourself what happens.
From the chemical analysis of cell membranes, it was discovered that cell membranes are
composed of phospholipids.
o Phospohlipids look a lot like clothespins with a polar(attracted to water) head and 2
nonpolar (repels water) tails.
polar head
nonpolar tails
1) When phospholipids are put in water, could you think of a way that they might arrange themselves
so that like is near like (i.e. polar is near polar, and nonpolar is near nonpolar). Sketch your
arrangement and then provide a justification.
Sketch:
Justification for sketch (Based on evidence above and evidence from our lab activities):
Name________________________________________
Date_______
3) When you placed cells in high concentrations of salt, what did you observe about the responses of
the cell wall and the cell membrane? How were they similar and how were they different? Be
specific.
4) What might that tell you about the structure of the cell wall versus the cell membrane? Explain.
5) Not all molecules that a cell needs are going to be able to enter a cell by diffusion through the cell
membrane. Give two examples of molecules that a cell might need and explain why they can't
enter by diffusion.
6) Think of two mechanisms by which these molecules might be able to enter the cell. (Hint: Think
of how animals take food into their bodies or how humans get water where it is needed.)
Name________________________________________
Date_______
7) Based on our lab activities, list the properties of the following molecules.
Molecule
Example
Charge (0 for
(if
neutral, ++ for
applicable) highly
charged, + for
slight charge)
Size (+ for
small, ++ for
medium, +++
for large)
soluble, ++
Solubility in
oil (0 for not
soluble, + for
slightly
soluble, ++
for highly
soluble)
Solubility in
water(0 for
not soluble, +
for slightly
for highly
soluble)
Carbohydrate
Glucose
Protein
Fat*
Salt
Water
Oxygen*
Carbon dioxide*
*Cannot measure conductivity of this substance.
8) Based on our discussion, which of these molecules will be able to cross the cell membrane by
diffusion?
a. Which won't?
9) What characteristics of the molecules can you use to determine whether they will cross the cell
membrane or not? Explain your answer.