Cell & Molecular Biology
Movement Across Biological Membranes
Homework #3
Answers
Membrane Fluidity
For each of the following situations, choose if the membrane will be more or less fluid:
1. More double bonds in the fatty acid
tails of phospholipids
2. Longer fatty acid tails of phospholipids
3. Phospholipids with unsaturated fatty
acid tails
4. Higher temperature
MORE
LESS
MORE
MORE
Transport mechanisms
Given the information below, predict by what process (simple diffusion, facilitated
diffusion, or active transport) the three molecules can move into the cell through this cell
membrane.
A is a charged molecule.
B & C are very small molecules that can pass through a semi-permeable
membrane.
Outside cell
Hi conc of A
Hi conc of B
Lo conc of C
Key
= channel for charged molecule
Inside cell
Lo conc of A
Lo conc of B
Hi conc of C
= lipid bilayer
A by _____FACILITATED DIFFUSION_______
B by _____DIFFUSION____
C by _____ACTIVE TRANSPORT_____
Osmosis
A demonstration was set up to illustrate the process of osmosis. Three balloons, made of
a semipermeable membrane, and three jars were filled with a 0.05M, 0.15M, or 1M
aqueous salt solution as indicated in the table below.
Jar
A
B
C
Salt Solution
0.15M NaCl
1.00 M NaCl
0.05M NaCl
Each balloon contains 0.15M NaCl
Key:
= Balloon
A
B
= Jar
C
Describe what will happen to each balloon when placed in the jar (expand, shrink or
stay the same size):
Balloon in jar A will _____ SAME ______ .
Balloon in jar B will ____ SHRINK _____ .
Balloon in jar C will ____ EXPAND _____ .
Describe the relationship between the solution and the balloon in each jar as
hypertonic, isotonic, or hypotonic:
Solution in jar A is _____ISOTONIC_____ ..
Solution in jar B is _____HYPERTONIC___ ..
Solution in jar C is _____HYPOTONIC___ ..