Lesson Title: Polysaccharides
Activity: Polysaccharide model
Grade:
9-10
Content Areas: Science
Lesson’s Time Block: 1 hour
Grouping: Students will work individually for the first half of class and in groups of four for
the last half as they build their polysaccharides molecules.
-------------------------------------------------------------------------------------------- Pre-planning tasks
EALRs/GLEs/PEs
9-11 PS2E Molecular compounds are composed of two or more elements bonded together
in a fixed proportion by sharing electrons between atoms, forming covalent bonds. Such
compounds consist of well-defined molecules. Formulas of covalent compounds represent
the types and number of atoms of each element in each molecule.
9-11 PS2F All forms of life are composed of large molecules that contain carbon. Carbon
atoms bond to one another and other elements by sharing electrons, forming covalent
bonds. Stable molecules of carbon have four covalent bonds per carbon atom.
9-11 PS2G Chemical reactions change the arrangement of atoms in the molecules of
substances. Chemical reactions release or acquire energy from their surroundings and
result in the formation of new substances.
Objectives (Learning Targets):
By the end of this lesson, students will create a model of alpha glucose that correctly
shows:
1) What an alpha glucose molecule looks like
2) How two glucose molecules bond with each other to form a new molecule
3) Water is released when glucose molecules bond with each other
4) That energy is needed to break apart those bonds to make simple sugars and
enzymes help reduce the energy needed. More energy is released when the bonds
are broken.
Rationale:
Flour, the major component of bread, is primarily made of starch. That starch is a
polysaccharide made of multiple glucose molecules (simple sugars). When bread is
made, the enzymes in the yeast break down the starch into smaller glucose molecules.
Those smaller glucose molecules can be used by the yeast for energy. This process of
creating and breaking apart sugar molecules is constantly occurring at all levels of the food
chain. Understanding the chemical composition of glucose and more complex starches is
an important part of understanding biology.
Essential Question: What does a 3-D glucose molecule look like and how does it bond
with other glucose molecules to form carbohydrates?
Unit: Bread
Lesson: Polysaccharides
Page: 1
Academic Language and Pre-requisite Knowledge: A basic understanding of the atom,
protons, neutrons and electrons. The structure of a glucose molecule and the carbon
tetrahedron.
Academic Language Target: By the end of the lesson, students will know about
polysaccharides as demonstrated in the building of their models.
---------------------------------------------------------------------------------------------------- Lesson Setup
Lesson Opening:
1. Focus question/ Anticipatory set: Show the students a sample of flour, water and
yeast that is actively rising in a jar. Explain to them that the flour is mostly starch.
Starch is a larger “polysaccharide” (poly=many, saccharide = sugar) made up of
multiple smaller glucose molecules. The yeast is breaking down some of the starch
in order to use it as food.
I will be specifically introducing “Freddie B. Levain”, a sourdough born on
February 14th, 2009. Started from whole wheat flower and water. It has been
kept alive and used for many loaves of bread ever since.
By the end of the lesson the students will build an alpha glucose molecule and join
them together to form polysaccharides.
2. In order to get each student participating and paying attention, the students will
create their own glucose molecule individually. The students will then work in
groups using their individual glucose molecules. The group will join their glucose
molecules together to build a larger starch molecule (polysaccharide).
----------------------------------------------------------------------------------------------------- Lesson Body
Lesson: (can be: I do it – you do it – we do it)
Show a sample glucose molecule (alpha glucose) using the gum drops and toothpicks.
The students will be building this during practice.
--------------------------------------------------------------------------------------------- Extended Practice
In Class Practice or work:
The images below are of the same glucose molecule from different angles.
The chemical formula is C6H12O6.
Give each student 6 black gumdrops (for carbon), 6 red or pink gumdrops (for oxygen) and
12 white gumdrops (for hydrogen). Toothpicks will be used to represent the bonds. Have
them each build a glucose molecule.
Unit: Bread
Lesson: Polysaccharides
Page: 2
Step 1: Poke 4 toothpicks into each carbon atom. Each toothpick should be 120 degrees
from each other and form a tetrahedron as see here:
Step 2: Poke 2 toothpicks into each oxygen atom. They should also be 120 degrees
apart.
Step 3: Poke 1 toothpick into each hydrogen atom.
Step 4: Using the diagrams below, connect the 5 carbon atoms and 1 oxygen atom to
form the main ring.
Note that the carbon tetrahedron should alternate pointing up and pointing down. Starting
with the oxygen being up, clockwise, to the first carbon, the tetrahedron points down,
position 2 points up, position 3 points down, etc. Where a connection is done, remove one
of the toothpicks so there is only 1 toothpick between each atom. Each toothpick
represents the sharing of an electron from each atom to form 1 covalent bond.
Step 5: Add the CH2OH to point up from position 6.
Step 6: Add an H to each of the remaining O to form OH.
Step 7: Add the OH to carbon 1, 2, 3, and 4. For an alpha glucose, OH should be down
on carbon 1, 2 and 4. It should be up on carbon in position 3.
Step 8: Add an H to the remaining bonds.
For this class, use the alpha glucose (the first one)
Note that the images below are for beta glucose, so the OH in position 1 should change
places with the H to form an alpha glucose.
Unit: Bread
Lesson: Polysaccharides
Page: 3
Step 9: In groups of 3 or 4: Using each person’s alpha glucose molecule, create a
polysaccharide by joining the OH in position 1 of one glucose with the OH in position 4 of
another glucose. During the bond, water H2O is created. The resulting bond only has an
O between the glucose. See the diagram below.
Images pulled from http://www.worldofmolecules.com/3D/glucose_3d.htm
and http://umanitoba.ca/Biology/lab2/biolab2_2.html
Homework:
Show the students where to find the nutrition information on food labels. Look at the
nutrition information for various foods. Choose 3 foods and write the name of the food and
number of grams of carbohydrates per serving. Try to find some with a lot and some with
a little carbohydrates so we can compare them. Bring the list to class for discussion about
where those carbohydrates typically come from.
--------------------------------------------------------------------------------------------------- Lesson Closing
Closure:
Review:
Unit: Bread
Lesson: Polysaccharides
Page: 4


Glucose bonds with other glucose to form complex carbohydrates (starch)
Starch is what makes up 70% of flour
Back to bread
 Yeast needs to break down the carbohydrates into glucose it can use
 Enzymes in yeast help break down the starch.
 Enzymes in your mouth can do the same thing. After the class, try a small piece of
un-buttered bread and chew it for a while. You’ll notice it gets sweeter as the
enzymes in your mouth break it down into simple sugars.
--------------------------------------------------------------------------------------------------------- Evaluation
Assessment:



Creation of a glucose molecule (effort will count as 75% of grade)
Creation of starch model. For every bond, a water molecule should be released.
Completion of homework.
Family Interactions:
Parents can help students find foods in their house with the different amounts of
carbohydrates.
Accommodations:
Handouts will be given to all students with the glucose and starch models.
Actual models will be available in the front of the class. That will help any student who
cannot understand the 3-D diagram as seen on paper.
Extension:
If the students are moving quickly through the material and making of the model, they can
change their alpha glucose to a beta glucose by switching the H and OH in position 1. If
they join the beta glucose molecules together at position 1 and 4, flipping every other one,
they will form cellulose. The diagram is below:
Materials:
Black, red and white gumdrops
Toothpicks
Unit: Bread
Lesson: Polysaccharides
Page: 5
Handouts with diagrams
References:
Steane, Richard (2008, January 4). Bio Topics - Structure of the glucose molecule.
Retrieved 1 October, 2011 from
http://www.biotopics.co.uk/as/glucose2.html
This website has very useful diagrams of glucose, maltose and amylose.
Steane, Richard (2008, January 4). Bio Topics - Jmol contents table. Retrieved 1 October,
2011 from
http://www.biotopics.co.uk/JmolApplet/jcontentstable.html
This website has 3-dimensional models of many molecules, including glucose,
maltose and amylose. It allows you to look at them from the side and from the end.
It shows the spiral appearance of amylose.
Exploratorium (1993). Science of Cooking: Bread Science & Facts | Exploratorium.
Retrieved 2 October, 2011 from
http://www.exploratorium.edu/cooking/bread/index.html
http://www.exploratorium.edu/cooking/bread/activity-yeast.html
The entire Exploratorium website is all about science. It has much more than just
cooking and bread science. There are many contributors and the National Science
Foundation supports them as well through a grant. Very good website with lots of
ideas and information.
EdInformatics (1999). Glucose Molecule - 3D – Jmol. Retrieved 2 October, 2011 from
http://www.worldofmolecules.com/3D/glucose_3d.htm
This website also has useful 3-D diagrams of molecules. It allows you to rotate the
molecules to any angle.
Unit: Bread
Lesson: Polysaccharides
Page: 6
Handouts for Bread Lesson 2
Carbon tetrahedron (shown here with hydrogen attached)
Available covalent bonds: C=4, O=2, H=1
For this class, use the alpha glucose (the first one)
Step 1: Poke 4 toothpicks into each carbon atom (black). Each toothpick should be 120
degrees from each other and form a tetrahedron.
Step 2: Poke 2 toothpicks into each oxygen atom (red or orange). They should also be
120 degrees apart.
Step 3: Poke 1 toothpick into each hydrogen atom (white or yellow).
Step 4: Using the diagrams below, connect the 5 carbon atoms and 1 oxygen atom to
form the main ring.
Note that the carbon tetrahedron should alternate pointing up and pointing down. Starting
with the oxygen being up, clockwise, to the first carbon, the tetrahedron points down,
position 2 points up, position 3 points down, etc. Where a connection is done, remove one
of the toothpicks so there is only 1 toothpick between each atom. Each toothpick
represents the sharing of an electron from each atom to form 1 covalent bond.
Step 5: Add the CH2OH to point up from position 6.
Step 6: Add an H to each of the remaining O to form OH.
Step 7: Add the OH to carbon 1, 2, 3, and 4. For an alpha glucose, OH should be down
on carbon 1, 2 and 4. It should be up on carbon in position 3.
Step 8: Add an H to the remaining bonds.
Step 9: To make a polysaccharide, connect the molecules at position 1 and 4 as shown
below. The O between each molecule holds them together and H2O is released.
Unit: Bread
Lesson: Polysaccharides
Page: 7