SAM Teachers Guide
Lipids and Carbohydrates
Overview
Students will explore the structure and function of two of the four major
macromolecules, lipids and carbohydrates. They will look specifically at the polarity of
the molecules and how polarity affects their solubility and behavior in different
environments. Students will apply their understanding of intermolecular attractions,
three-dimensional structures of molecules, and electronegativity to these specific
molecules.
Learning Objectives
Students will be able to:
 Explore organic compounds and identify the carbon backbone.
 Recognize what makes carbohydrates polar and determine how polarity affects
the solubility of the molecule.
 Define lipids as molecules that dissolve in fats.
 Compare and contrast the properties of lipids and carbohydrates.
 Explore the structure and function of various polysaccharides.
Possible Student Pre/Misconceptions
 Lipids and carbohydrates are giant and confusing molecules.
 Lipids and carbohydrates are taken in the body to give energy and then leave.
 Muscles turn into fat if you don’t continue to use them.
 Fat is bad for you.
Models to Highlight and Possible Discussion Questions
After completion of Part 1 of the activity:
Models to Highlight:
 Page 3 – The Importance of Polarity
o After running the model, review with students why ethylene boils
first. Use this as an opportunity to review the terms polarity,
electronegativity, and intermolecular attractions.
o Link to other SAM activities: Intermolecular Attractions. Students
can discuss how the strength of intermolecular attractions relates to
boiling point.
 Page 5 – Changing Solvent

o Highlight the fact that the lipid remains clustered together when
placed in water as a solvent. Yet, when placed in oil, the lipid
particles spread out. Review the terms hydrophobic and
hydrophilic and how they relate to solubility.
Page 6 – Lipid Bilayers
o Review what types of materials can pass through the cell
membrane and why. Highlight why the bilayer is arranged as it is,
referring to the “heads” and “tails.”
o Link to other SAM activities: Diffusion, Osmosis, and Active
Transport. Students can discuss what they remember about how
particles move and why. They can also discuss the fate of molecules
that cannot pass through membranes passively.
Possible Discussion Questions:
 How does the presence of oxygen in a hydrocarbon change its properties?
How does oxygen affect the polarity of a molecule? Why?
 Explain the difference between the terms hydrophobic and hydrophilic.
 If one molecule has both hydrophobic and hydrophilic regions, how
might this affect its behavior in different solvents?
 Why do people say, “oil and water don’t mix”? Explain this phrase using
what you now know.
 Why do you think cells evolved to have a lipid bilayer? Why is this type of
protective coating particularly advantageous?
After completion of Part 2 of the activity:
Models to Highlight:
 Page 7 – Comparing the Solubility of Sugars and Hydrocarbons
o After students have run the model, highlight the link between
polarity and solubility in water.
o Link to other SAM activities: Solubility. Highlight how
electrostatic distribution of charge is related to polarity and a
molecule’s ability to dissolve.
 Page 8 – The More Hydrogen Bonds, The Stronger the Polysaccharides
o Students can discuss why it was difficult to pull apart the two
chains of polysaccharides.
o Link to other SAM activities: Intermolecular Attractions. Highlight
how hydrogen bonding is optimal when the chains are linear and
how the shape of the two molecules allows them to line up close
together.
 Page 10 – Energy in Polysaccharides
o Highlight the difference in energy released between the branched
and unbranched molecules (starch vs. glycogen).
o Link to other SAM activities: Chemical Bonds and Molecular
Geometry. Use this as a chance to review the energy stored in
chemical bonds and how the shape of molecules influences their
behavior.
Possible Discussion Questions:
 Structurally, what are some differences between lipids and carbohydrates?
Will these differences affect their function? Why or why not?
 What about the structure of polysaccharides makes them good “building
materials” in living systems?
 What is the difference between linear and branched polysaccharides in
how they behave at different temperatures? Why?
 Why would plants be satisfied storing energy in starch molecules while
animal cells use glycogen for short-term storage? Refer to what you
remember from the model on page 10. What does branching have to do
with the amount of chemical energy released as enzymes attack?
Connections to Other SAM Activities
The focus of this activity is on the basic structure and function of both lipids and
carbohydrates in biological systems.
The Lipids and Carbohydrates activity is supported by many other SAM activities. The
Electrostatics activity helps students learn about charges in atoms; Chemical Bonds
explores the different types of bonding patterns that result from different patterns of
sharing electrons; and Intermolecular Attractions helps students to predict and
understand what happens between molecules once these chemical bonds have formed.
These activities help students understand the polar nature of carbohydrates and the
non-polar nature of lipids. The Solubility activity helps students relate the properties of
the molecules to the environment in which they are found. Finally, Molecular
Geometry supports learning about the structure of both carbohydrates and lipids and
how structure relates to function.
This activity supports both Diffusion, Osmosis, and Active Transport and Molecular
recognition. In both of these, knowledge of the basic structure and function of lipids is
helpful in understanding lipid membrane systems.
Activity Answer Guide
The oxygen atoms make ketene a polar
molecule, increasing the attraction between
partial positive and partial negative ends of
molecules. Therefore, it requires more energy, in
the form of heat, to break the molecules apart
and cause the liquid to boil.
Page 1:
Introduction, no questions.
Page 2:
1. Hydrocarbons are referred to as organic
molecules with a "backbone." Take a
snapshot of the hydrocarbon you created
and drag the snapshot into the box below.
Use the arrow tool to point to the carbon
backbone.
Page 4:
1. Which of the following are true? (a) (b) (c)
2. Take a snapshot of a lipid that is fully
dissolved (evenly spread in the solvent).
Sample snapshot: Lipids evenly spread in the
solvent.
Sample snapshot: Hydrocarbon molecule
created.
2. How many bonds does every carbon atom
have?
Four (4)
Page 3:
1. Why do you think the charge arranges
itself for ketene in this way?
The negatively charged electrons are attracted
to the oxygen atom. Since the oxygen end of the
molecule attracts more of the negative charge,
the remainder of the molecule is left partially
positive.
2. Which compound boils first?
(a)
3. How does the presence of the oxygen
atoms in the molecule account for the
difference?
3. Hydrophilic means something is attracted
to water and hydrophobic means something
is excluded from water because water is
more attracted to other water molecules than
to it. Are the lipids hydrophobic or
hydrophilic? Explain your answer.
The lipid molecule is hydrophobic. This is
apparent because the lipid molecule is not
dissolving in water. The water molecules are
more attracted to each other than they are to the
fat. This results in the lipid remaining together as
a clump.
Page 5:
1. What can you tell about the properties of
the fatty acid from observing it? Check all
that apply.
(a) (c) (f)
2. Compare the structure and the polarity of
the fatty acid to the hydrocarbon.
The hydrocarbon is non-polar (neutral) while the
fatty acid is polar. The carboxyl head on the fatty
acid has oxygen atoms that attract more
negative charge.
3. Explain why the tails are located in the oil
and the heads in the water.
The tail of the molecule is a long hydrocarbon
chain that is hydrophobic. The head is a polar
carboxyl group that makes it hydrophilic. So
water molecules attract the heads, but not the
tails.
4. Why are fatty acids compared to the twofaced deity Janus?
(c)
5. Take a snapshot of the lipid structure in
water. Drag the snapshot into the box below.
The oil forms clusters on the surface of the soup
because they are not soluble in the water-based
soup. The fat molecules are excluded from the
water.
Page 6:
1. Which statement about membrane
phospholipids is NOT true? (e)
2. Membranes can keep chemicals inside
and outside of the cell. What would happen if
a cell membrane breaks?
If the cell membrane breaks there would be no
regulation of what can enter and leave the cell.
Page 7:
1. How is the lipid molecule different from
the sugar molecule? (Check all that apply.)
(b) (c)
2. An increase in the ratio of oxygen atoms
to hydrogen and carbon... (Check all that are
true.)
(a) (c)
Sample snapshot: Fatty acids in water.
3. Select a snapshot image that shows
benzene molecules do not mix well with
water molecules.
6. Take a snapshot of the lipid structure in
oil. Drag the snapshot into the box below.
Sample snapshot: Fatty acids in oil.
7. Have you ever observed beads of oil on
the surface of soup? Explain how this model
can help explain the occurrence of those
beads.
Sample snapshot: Benzene with water
molecules.
4. Fill in a snapshot image that shows
glucose molecules mix better with water
molecules.
apart more easily whereas wood’s linear nature
makes so many more attractions between
molecules, and they do not break apart Easily.
Page 10:
1. Which substance produces more
chemical energy, starch or glycogen, when
enzymes work on it? Why?
Glycogen produces more chemical energy
according to the bar graph. Because it is more
highly branched, it has more "ends" for the
enzymes to attack.
Sample snapshot: Glucose with water
molecules.
5. Explain how the presence of six OH
groups affects the solubility and properties
of glucose.
The presence of six OH groups makes glucose
a polar molecule. The uneven distribution of
charge increases its solubility in water, which is
also polar.
Page 8:
1. Cellulose is made of long polysaccharide
chains that line up in parallel. How does this
structure relate to its function?
When aligned together with strong bonds
between them, the molecules can act as
structure and protective coating of plants.
2. Long linear polysaccharides make strong
fibers because:
(d)
Page 9:
1. Branched polysaccharides can be more
easily separated into individual chains then
linear polysaccharides like cellulose. This is
explained by:
(d)
2. Based on your observations of the
polysaccharides in the models, explain why
starch is edible and wood is not.
Starch, a branched polysaccharide, has many
fewer intermolecular attractions because the
polymers cannot fit together tightly. They break
2. Which substance would produce more
chemical energy if enzymes could attack in
the middle of the chain rather than just at the
ends?
There would be less of a difference in the
chemical energy released if the enzyme could
attack anywhere in the molecule.
Page 11:
1. In the model to the left, three molecules
tagged as "A", "B" and "C" are placed in
water. Click the " " button to run the model
and observe what happens. Based on your
observation, can you tell which molecule is
the most polar?
(a)
2. Compare two hydrocarbon chains: one
that includes oxygen atoms and one without.
How does the presence of oxygen affect the
properties of a hydrocarbon chain?
(a)
3. What makes cellulose so strong? (a)
4. Describe why lipids are so important to
cellular evolution.
Scientists believe that the first step in cellular
evolution was the emergence of lipids. These
lipids are thought to have become more
complicated. Then, the lipids formed
membranes that created an interior space,
separating it from an outside environment.
5. Table sugar and wood are both made of
glucose. Why can you serve cubes of sugar
with tea, but not cubes of wood (without
offending your guests)?
The amount of branching in polysaccharides
impacts their structure, particularly at different
temperatures. Cubes of sugar will dissolve when
heated by being placed in hot tea while cubes of
wood will maintain their solid structure. This is
due to the increased attraction (hydrogen
bonding) in wood, which is linear as opposed to
sugar, which is branched.
6. Which statement about membrane
phospholipids is NOT true? (d)
SAM HOMEWORK QUESTIONS
Lipids and Carbohydrates
Directions: After completing the unit, answer the following questions to review.
1. What is the difference between a polar and non-polar molecule? How does this relate to
the term electronegativity?
2. What property affects a molecule’s solubility in specific solvents?
3. What will happen if you try to dissolve a lipid in water? If you change the solvent to oil,
instead of water, what will happen to the lipid? Why?
4. Phospholipids form the cell membrane. In the space below, draw how the phospholipids
arrange themselves in the cell membrane. Then, explain why this is the case given what
you know about the hydrophobic and hydrophilic parts of the molecules. Be sure to label
your drawing.
5. Write captions that explain what is happening to the phospholipids in the two pictures
seen below. Note: They are in water on the left and in oil on the right.
Caption:
Caption:
6. How do intermolecular attractions play a role in the behavior of polysaccharides?
SAM HOMEWORK QUESTIONS
Lipids and Carbohydrates – With Suggested Answers for Teachers
Directions: After completing the unit, answer the following questions to review.
1. What is the difference between a polar and non-polar molecule? How does this relate to
the term electronegativity?
Polar molecules do not share electrons evenly among atoms while non-polar molecules do. The term
electronegativity refers to how well an atom can attract electrons from another atom. Highly electronegative
atoms affect the polarity of molecules.
2. What property affects a molecule’s solubility in specific solvents?
Polarity. This goes back to the concept of “like dissolves like” when referring to solubility of macromolecules.
3. What will happen if you try to dissolve a lipid in water? If you change the solvent to oil,
instead of water, what will happen to the lipid? Why?
Following the rule that “like dissolves like,” a lipid will not dissolve in water, but will dissolve in oil. This has
to do with the intermolecular attractions between non-polar lipids and different solvents. Water is a polar
solvent while oil is a non-polar solvent.
4. Phospholipids form the cell membrane. In the space below, draw how the phospholipids
arrange themselves in the cell membrane. Then, explain why this is the case given what
you know about the hydrophobic and hydrophilic parts of the molecules. Be sure to label
your drawing.
In the bilayer, the polar, hydrophilic heads face out while the non-polar, hydrophobic tails
face inward, towards each other due to the intermolecular attractions.
5. Write captions that explain what is happening to the phospholipids in the two pictures
seen below. Note: They are in water on the left and in oil on the right.
Caption: Hydrophobic tails do not dissolve in water.
Caption: Hydrophilic heads do not dissolve in oil.
*The tails of the molecules are long hydrocarbon chains that are hydrophobic. The heads are polar carboxyl groups
that make them hydrophilic. So, water molecules attract the heads, but not the tails.
6. How do intermolecular attractions play a role in the behavior of polysaccharides?
Polysaccharides are formed by joining sugar molecules. They are held together by hydrogen bonds. The
strength of these bonds and the shape of the molecules (the degree of branching) play a role in their
multitude of functions.