Membrane Structure POGIL Answers
Membrane Structure POGIL Answers
Membrane Structure POGIL Answers
Model 1 – Phospholipids
Hydr
ophili
c
head
Hydro
phobic
tails
b. What portion of the molecule in Model 1 is responsible for the “-lipid” part of the name?
The fatty and acid chain
4. Label the regions of the molecule in Model 1 with the phrases “hydrophilic head” and “hydrophobic
tail.” Click on the molecule picture in Model 1 to edit
5. Scientists often use a cartoon representation like the one shown below to represent a phospholipid.
Which portion of the cartoon represents the hydrophilic head of the phospholipid?
Hydrophili
c head
6. When phospholipids are placed on the surface of water they form a thin layer. Consider carefully
which portion of the phospholipid will be in the water and which will be in the air in order to obtain the
most stable (lowest potential energy—maximum attractions) system. Draw a cartoon like
representation below to show the proper orientation of three phospholipid molecules on the surface
of water. Click on the diagram below to edit.
7. When a small amount of oil is added to a beaker of water containing phospholipids, the
phospholipids will surround the oil droplets forming micelles. Use several cartoon representations of
phospholipid molecules to show the arrangement or orientation of phospholipids in a micelle. Click on
the diagram below to edit.
8. Recalling that a beaker of water is three-dimensional, what is the three-dimensional shape of the
micelle?
Sphere
9. Phospholipids assemble in layers to make membranes for cells and organelles. Circle the
drawing below that represents the most stable (lowest potential energy) assembly of phospholipids
where water is both inside and outside of the membrane. (This might be the membrane on a vacuole
for instance.) Explain your reasoning. Click on the diagram below to edit.
I chose the big one because there are hydrophobic and hydrophilic heads on the inside and
outside which help it function better.
Read This!
When phospholipids are added to an aqueous environment (consisting mostly of water) the
phospholipid molecules will spontaneously assemble into a phospholipid bilayer where the layers are
held together by weak attractive forces between molecules. These structures are often seen in
nature as cell and organelle membranes.
11. Consider animal cells, which are only bound by a cell membrane and plant cells which are bound
by both a cell membrane and a cell wall. Are cell membranes flexible (fluid)?
The cell membrane are flexible. Because different cells within the body change shape or move
because of where its located. For example ameobas change shapes as it consumes food.
12. Explain why a phospholipid bilayer is flexible in terms of the strength of the forces that hold it
together.
A phospholipid bilyar is flexible in terms of the strength of the force that holds it together because it is
held together by weak hydrophic interactions which allows it to move more freely.
b. Explain why the flexibility (fluidity) of a membrane increases when more of the
phospholipids in the layers contain double bonds.
When the tails are bent, the molecules cannot assemble as tightly when when it increases.
14. The diagram below shows the chemical structure of cholesterol, which is a key component of
membrane structure.
b. Circle the drawing below which illustrates the most likely placement of cholesterol in a
phospholipid bilayer. Click on the diagram below to edit.