Title: Making and Breaking Carbohydrates: How living things get energy!
Author : Meredith Schwendemann
Subject Area(s): Science
Grade(s): 8
Description of Lesson: Students will learn how the sun provides all living things with energy
through the processes of photosynthesis and cellular respiration; through the formation and
breakdown of carbohydrates. The lesson includes music and technology with the incorporation
of a music video about photosynthesis, note-taking with processing and summarizing, and a
hands-on lab demonstration to test for starch and witness the breakdown of starch into simpler
sugars. The lesson will conclude with an assessment to measure student learning.
Length of Lesson: 3- 42 minute sessions
Student Objectives: Students will understand that energy for living things comes from the sun
through the processes of photosynthesis and cellular respiration. Students will recognize and
recall specific vocabulary: carbon, carbohydrate, starch, glucose, organic compound,
photosynthesis, cellular respiration.
Materials:
Teacher computer with internet access and projector
Interactive Science Notebooks (students have their own to record their notes and summaries)
Copy of readings or textbook with content information (McDougal Littell Science, Cells and
Heredity, Chapter 2, pgs 41-42, 47-54)
Music Video: "Photosynthesis - They Might Be Giants" found on Youtube
http://www.youtube.com/watch?v=LgYPeeABoUs
Two colors of construction paper with string- 10 pieces of color 1 and 12 pieces of color 2
Starch to Sugar Handout (class set) from Missouri 8th Grade Level Lab Book- B.K. Hixson.
Loose in the Lab. 2009. (an adapted version of this handout is included at the end of the
lesson)
Materials for lab activity (per lab group): 2-4 saltine crackers, 2 dixie cups, 2 craft sticks, iodine
solution, water, 1 pipette
Procedure:
Day 1:
Preview Content and assess prior knowledge: Show the music video, "Photosynthesis- They
Might Be Giants", and have students record information they see and hear from the video.
Make a list of what students already know about photosynthesis and how living things get
energy.
Input: Students use Cornell-style notes to add information about the key terms: Carbon,
Carbohydrate (starch, glucose, cellulose), Organic Compound, Photosynthesis, Cellular
Respiration. Students put the notes in their interactive science notebooks.
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Carbon: student read the paragraph about carbon found in the readings for this class
(project on screen or provide handouts), record information in notes, select students to
demonstrate carbon's bonding ability. Have 10 students represent carbon atoms (hang
color 1 around each student representing carbon), have 12 students represent hydrogen
atoms (hang color 2 around each student representing hydrogen). Have two carbons
stand back to back with their arms outstretched at right angles so that there are four
hands, one in each direction. These students represent one carbon atom that has the
ability to bond four times. Have the other students representing carbon form carbon
atoms. Have one student from each carbon pair hold hands with a student from another
carbon pair forming a carbon chain. Then have students representing hydrogen only
extend one arm, keep the other arm at their sides. Have students representing
hydrogen hold hands with the free hands of the carbon atoms. Point out to students that
hydrogen can only form 1 bond, but carbon can form 4 allowing it to be the building
blocks for important organic compounds for life. (extension: you could add an element,
oxygen, by using a 3rd color. Students would extend both arms, showing that oxygen
can form a double bond with carbon, or two bonds between two atoms)
Have students draw a picture in their notes to represent carbon and how carbon bonds.
Organic Compound: students read the paragraphs about organic compounds in the
handout for this class. Record information about organic compounds in their notes.
Students may also read other resources about organic compounds to provide additional
examples in notes (McDougal Littell Science, Chemical Interactions, Chapter 5) Have
students add to their list of examples by thinking of organic compounds in their own
lives.
Carbohydrate: students read about carbohydrates (pg 274-275 in handout) or in
McDougal Littell Science, Cells and Heredity, pg 42, or in McDougal Littell Science,
Chemical Interactions, chapter 5). Have students teach the information they read about
to their seat partner for 30 seconds to a minute. Have students record important
information about carbohydrates in their notes. Have students draw pictures
representing carbohydrates in their notes- pictures may include examples of where
carbohydrates are found, or pictures of the molecular structure of carbohydrates. Ask
students to identify the last food containing carbohydrates they ate.
Photosynthesis: pose the question, how are carbohydrates made? Read information
about photosynthesis in the handout (pgs 271-272) or pages 47-49 in McDougal Littell
Science, Cells and Heredity. Have students summarize/teach their seat partner about
photosynthesis. Record information in notes. When students record the equation for
photosynthesis, highlight the reactants in one color and the products in another.
Emphasize that the energy for the reaction comes from the sun, but is not destroyed, it is
transformed into chemical energy in the form of glucose (sugar).
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Cellular Respiration: pose the question, how do living things access the energy stored in
sugars? Read information about cellular respiration in the handout (pgs 272-273) or in
McDougal Littell Science, Cells and Heredity, pgs 50-51. Have students teach their seat
partner about cellular respiration. Record information in notes. When students record
the equation for cellular respiration, highlight the reactants in one color and the products
in another. Emphasize that the chemical energy stored in glucose (sugar) has not been
destroyed, but converted into another usable form of energy. Ask students if they see
anything interesting about the equations for photosynthesis and cellular respiration.
Processing activity: have students create a Venn diagram comparing and contrasting
photosynthesis and cellular respiration.
Summary: students summarize why living things need carbohydrates, how carbohydrates are
formed, and how energy is released from carbohydrates.
Day 2:
Starch to Sugar Lab pgs. 178-179 in Missouri 8th Grade Level Lab Book, B.K. Hixson, Loose in
the Lab, 2009. Students will learn how to test for starch using iodine and understand how the
body begins to break down starch in preparation for cellular respiration.
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Review lab safety rules.
Read lab handout with students. (see attachment at end of lesson)
Carryout lab procedures and record observations in data table
Answer lab analysis questions
Day 3:
Review concepts from previous two days. Have students watch the music video
"Photosynthesis- They Might Be Giants" again and look for ways to improve the information in
the video. Have students do a think-pair-share on what could be added to the video to make it
better. Record student ideas on the board. Student ideas may include better images/animation
to help explain the content, or additional content that was glazed over in the video.
Have students answer the assessment questions to measure how well students learned the
concepts. Note: the assessment questions could be used on day 1 as a pre-test in order to
measure student gain from the beginning to the end of the lesson.
Scientific Explanation: Carbohydrates are organic compounds made of carbon, hydrogen,
and oxygen. They are necessary for living things because they provide energy for life.
Carbohydrates are made during the process of photosynthesis and the energy stored in
carbohydrates is released during the process of cellular respiration.
Assessment:
1. Explain why carbon is the major element of life; include the term organic compound in your
answer. answer: Carbon has the ability to bond with many different elements in many different
ways due to the fact that it has 4 valence electrons. Carbon is the basis of all organic
compounds because of it's ability to bond. Carbon can be linked together in long chains to form
large molecules necessary for life.
2. What functions do carbohydrates perform for living things? answer: carbohydrates provide
living things with energy.
3. List two examples of carbohydrates. answer: Starch, glucose, cellulose.
4. How do plants and animals get energy? answer: plants get energy through the process of
photosynthesis. Photosynthesis uses sunlight, CO2, and H2O to make glucose which is used
for energy. Animals get energy by eating plants and other animals and breaking down glucose.
5. Why is photosynthesis important to life on earth? answer: it uses energy from the sun to
produce energy for most living things on earth.
6. What are the starting materials for photosynthesis? answer: CO2, H2O, sunlight.
7. What are the starting materials for cellular respiration? answer: glucose, O2.
8. How are photosynthesis and cellular respiration similar? How are they different? answer:
cellular respiration and photosynthesis both transform energy, but the starting materials and the
products are reversed in the two processes. Photosynthesis uses carbon dioxide and water to
convert light energy to chemical energy (glucose). Cellular respiration uses glucose and oxygen
and produces carbon dioxide and water and transform the chemical energy into another usable
form for the body.
(questions 2, 7, 8 taken from McDougal Littell Science, Cells and Heredity, Chapter 2)
Missouri and Kansas Standards Addressed:
Kansas Science Standards:
Standard 3, Benchmark 5: The student will understand living systems require a continuous input
of energy to maintain their chemical and physical organization. Students understand the sun is
the primary source of energy for life through the process of photosynthesis. Students
understand food molecules contain biochemical energy, which is then available for cellular
respiration.
Missouri Science Standards (GLE’s):
Strand 3.2, Concept B. Photosynthesis and cellular respiration are complementary processes
necessary to the survival of most organisms on Earth.
Strand 1. 2, Concept A.a. Recognize and describe how chemical energy is stored in chemical
compounds (e.g., energy stored in and released from food molecules, batteries, nitrogen
explosives, fireworks, organic fuels)
Starch to Sugar with your host: Amylase
Lab Group Members: ____________________________________________________________
The Experiment
The digestive process starts in your mouth, when you begin to chew your food- something we
are confident your mother has instructed you to do on more than one occasion. Your mouth is full of
enzymes. An enzyme is kind of like a chemical key. Enzymes are proteins that unlock long chains of fat,
protein, and starch molecules, and releases them as shorter, easier-to-handle molecules, like amino
acids and sugars (glucose, fructose, sucrose…).
To demonstrate this idea, we are going to ingest a cracker, a food that you will test and
determine is made almost exclusively of starch. Rather than swallowing the cracker right away, you are
going to keep chewing it to make a cracker mash. As you do, the enzymes in your mouth will continue
to break the starch down into sugar. When you perform the test for starch a second time, it will come
up negative, because most of the starch has been unlocked and converted into smaller pieces.
Background information
One enzyme present in your saliva is called amylase. Amylase breaks down starch molecules
into smaller sugar molecules. Recall that starch and sugars are examples of carbohydrates;
carbohydrates store chemical energy. The enzyme amylase is a protein. Amylase is a protein that
speeds up the breakdown of large molecules, a catalyst in chemical reactions.
Iodine is a starch indicator. Normally, iodine is a reddish-brown colored liquid. You may have
used it to treat minor cuts and scrapes, it leaves a reddish-brown color on your skin. When iodine
comes into contact with starch, it reacts to form a deep blue-black color. Scientists use iodine to
determine if starch is present.
Pre-lab questions
1. Which cells need energy? ________________________________________________________
2. Which process releases energy from sugar molecules?__________________________________
3. What are the starting materials for this process (the reactants)? __________________________
______________________________________________________________________________
4. When you ingest food, are the starting materials for this process ready to go? _______________
5. What must your body do to the food in order to prepare it for cellular respiration? ___________
_____________________________________________________________________________
Materials:
2-4 saltine crackers
Student Roles:
2 dixie cups
Timer
2 craft sticks
Chewer
iodine
Recorder
water
Messenger
1 pipette
Procedure
1. Take one saltine cracker and mash it in a Dixie cup using your fingers. Make the pieces as small
as you possibly can. Add a pipette full of water to the cracker and mix everything around with
the craft stick to make a lovely and appetizing cracker mash.
2. Send one student to the front table with the Dixie cup and cracker mash to receive a pipette full
of iodine. Record what happens to the color of the iodine when it hits the mixture.
3. Take the second cracker, pop it into your mouth, and chew it up. Chew for about 2 minutes, the
longer you chew the longer the amylase has time to break starch down into simpler sugars.
Note any change in flavor as you chew, particularly any sweetness.
4. After two minutes of chewing, spit the cracker mash into the second Dixie cup.
5. Send one student to the front table with the second Dixie cup and chewed cracker mash to
receive a couple of drops of iodine. Note the color of the iodine after it is added to the cracker
mash. If starch is present, the color will change to a deep black. If there is no starch present,
the color will remain reddish-brown.
Data and Observations
Observation table: Effect of amylase (protein) on starch molecules (carbohydrate)
Cracker with water and iodine
Cracker with amylase and iodine
Additional observations: ________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Concluding Questions
1. Was there starch present in the crackers before the experiment was begun? ________________
2. How do you know? ______________________________________________________________
______________________________________________________________________________
3. Was there starch present in the cracker mash after it had been chewed for 2 minutes? ________
4. How do you know? ______________________________________________________________
______________________________________________________________________________
5. What was the function of the enzyme (protein) in your saliva? ___________________________
______________________________________________________________________________
6. Why do we (animals) need enzymes like amylase? _____________________________________
______________________________________________________________________________
______________________________________________________________________________
7. Was this an example of mechanical (physical) digestion, or chemical digestion?
______________________________________________________________________________
8. How do you know? ______________________________________________________________
______________________________________________________________________________
9. What were the constants in this experiment? _________________________________________
10. What was the independent variable in this experiment? ________________________________
11. What was the dependent variable in this experiment? __________________________________
How Come, Huh?
This lab gives you evidence of what happens in the digestive process. The process starts the
minute the grits hit the roof of your mouth. The enzymes in your mouth start to flow when your nose
smells food cooking. You’ve heard the expression, “Mouth-watering good food”? Well, that’s just your
nose telling your brain to inform your mouth that some good eatin’ is on the way and to fire up those
digestive enzymes. That’s why your mouth waters when you are hungry-- your body is getting ready to
eat!
The food hits your mouth and the enzymes go right to work, breaking large, complex protein
and carbohydrate molecules into smaller amino acids and sugars. The starch gets chopped up into
simple sugars that are needed for your cells to undergo cellular respiration.
Your mouth has three sets of glands that secrete saliva into your mouth. They are the parotid
gland, located in the back of your throat, the submandibular gland, located in your lower jaw, and the
sublingual gland, located under your tongue. Working in concert, these three glands can secrete as
much as 2 liters of saliva per day- more if you drive by a hamburger joint venting its grill fumes out into
the street!
*Adapted from Missouri 8th Grade Level Lab Book. B.K. Hixson. Loose in the Lab. 2009.