Summary
Students explore the molecular makeup of starch and gather evidence from a research article on marine cryptomonad nutrient requirements to answer the essential question:
Essential Question(s)
Can people live on glucose alone, why or why not?
Snapshot
Engage
Post WWII Japan story about eating research-grade glucose hidden in an oceanside cave. Taste corn syrup.
Explore
Use a digestive enzyme to break down starch into glucose. Detect the conversion using reagents. Initial evaluation of essential question.
Explain
Analyze claims and evidence from an article on marine cryptomonad nutrient requirements. Develop a class definition of growth in terms of biomolecule function and composition. Construct an explanation for why our bodies need more than just glucose to grow. Re-evaluation of essential question.
Extend
Analyze matter and energy in biomolecule synthesis pathways. Think Pair Share activity to make thinking visible. Students prepare their "molecule break and build" lesson and pair up to video and teach one another.
Evaluate
Video of "molecule break and build" lesson.
Materials
1-2oz cups (condiment size)
mini tasting spoons or popsicle sticks
corn syrup
Benedict's Solution or diabetes glucose testing sticks
Engage
Go to slide 5. Ask students the formative assessment questions and collect their answers using a digital polling tool like Mentimeter.
Ask for students to share the reasoning behind their ideas, specifically the correct ones, to establish accurate conceptions for the first two questions. Do not address the third question at this time. Let students know they'll be exploring the ideas as they continue through the lesson. Be sure to reinforce that information throughout the rest of the lesson where it is meaningful in context, particularly if students do not demonstrate a strong understanding based on this formative assessment.
Distribute cups with a very small amount of corn syrup and tasting spoons/popsicle sticks for the students to taste. Let them know that the corn syrup is also called glucose syrup. While students are tasting the syrup go to slide 6. Tell the story while it's projected on the screen for students to follow along.
I once heard a story about this young person in Japan near the end of World War II. He and his family were close to starvation, but he looked in a cave near the coast and found that some researcher had hidden lab supplies there. Glucose was one of the supplies. The young person brought his siblings there and they all ate glucose out of syringes. After hearing this story, I made the partially serious comment that as long as these people had glucose to eat, they could survive.
Ask students: Why was this comment only partially serious?
Ask the students if the syrup can give them energy, then ask if it can sustain them for a long period of time. Students should agree that they get energy from the corn syrup, but cannot live on it alone.
Explore
Distribute the Biomolecule Builders Activity Sheet handout to students.
Go to slide 7. ADD BIOMOLECULE DEFINITION HERE SOMEWHERE. Students draw the glucose structure. Use the I Think/We Think strategy. Students write a claim about the nutrient glucose (question 2 in Biomolecule Builder Activity Sheet). Have a class discussion to arrive at claims about the matter and energy in the nutrient glucose. Students record these claims (question 2 in Biomolecule Builder Activity Sheet).
Go to slide 8. Ask questions that will prepare students to draw a conclusion about production and storage of glucose in the form of starch in plants. Expect that student answers will be incomplete at this time, but the investigation will help them develop more thorough understanding.
Go to slide 9 Show a video about extracting potato starch (a survival food): https://youtu.be/QjzdIYoIqrw. Stop this video around the 2:00 mark to avoid prematurely revealing that starch is converted to glucose. Tell students that they will do some tests on starch to construct an explanation about where and how plants store glucose molecules.
Students start Loaded Potato Investigation in Biomolecule Builder Activity Sheet, testing different combinations of iodine, amylase, and Benedict's solutions When added to starch, iodine should produce a purple mixture. Heated Benedict's solution should produce an orange solid when added to glucose.
Go to slide 10 after students have finished all the tests they plan to do. Have students take notes from this slide. Each student writes a conclusion about the production and storage of glucose in the form of starch in plants (question 3 in Biomolecule Builder Activity Sheet). To answer question 4 in Biomolecule Builder Activity Sheet, students use evidence from the Loaded Potato Activity to support claims generated as a class on slide 4 (Claims Concerning the Nutrient Glucose).
Go to slide 11. Students answer question 5 in Biomolecule Builder Activity Sheet, which instructs them to cite evidence from the Loaded Potato Activity and give reasoning for their response. Tell students that to gather more evidence, we are going to read a scientific article about a marine cryptomonad and what types of molecules it can eat/survive on.
Explain
Go to slide 11. Ask students: Why does this title specifically mention nitrogen? Students are assigned to 9 groups to complete the Claim, Evidence, Reasoning section and question 6 of the Biomolecule Builder Activity Sheet. Divide the claims up among the groups to ensure that each claim is addressed as a class. Have each group present their assigned claim while classmates take notes in the table in the Biomolecule Builder Activity Sheet.
Go to slide 12. The teacher will think aloud to the students while evaluating an example of weak evidence and an example of strong evidence. The teacher will ask the students to write down the key points from the teacher's example evaluation (question 7 in the Biomolecule Builders activity sheet). Students answer questions 8 and 9 in the Biomolecule Builders activity sheet.
Go to slide 13. The teacher asks the students what happens when cells grow. Guide discussion to work towards a class definition of growth (question 10 in the Biomolecule Builders activity sheet). At minimum students should determine that:
The cell will multiply.
The DNA will be replicated.
Proteins will be produced to do the work.
Students will draw on the cell picture to illustrate these three points and any additional points the class comes up with.
Go to slide 14. Students draw adenylate (question 11 in Biomolecule Builders activity sheet). Have a class discussion to prepare students to explain why people cannot live on glucose alone (question 12 on Biomolecule Builders activity sheet). Ask students to count the number of carbons in glucose and ribose and describe what would have to occur for the glucose to be used as a starting material to build adenylate. An example response is that one carbon would have to be ejected from glucose to form ribose.
Extend
Go to slide 15. Tell students that researches have actually already discovered the exact mechanism cells use to convert glucose to ribose to build nucleotides and eventually nucleic acids. Part of the nucleotide synthesis pathway called the pentose phosphate pathway is on slide 12. Give students the instructions below. Students will use the image of the pentose phosphate pathway on slide 12 as a reference to complete steps 1-2 below.
In the drawing for question 11 on the Biomolecule Builders Activity sheet, circle the atoms in glucose that are removed in the process of converting glucose to ribose.
Draw a red slash across the chemical bonds that were broken when these atoms were removed.
To reinforce the conservation of matter, use the pentose phosphate pathway mechanism to show that the "removed" carbon is ejected as CO2.
Go to slide 16. In steps 1 and 3-9 below, students answer questions 13-20 in the Biomolecule Builders Activity sheet. In step 2, the teacher will give verbal instructions.
Answer question 13: What is exchanged in the formation and breaking of chemical bonds? [Answer: energy]
Draw an arrow from the answer "energy" to one of the red slashes.
Answer question 14: Does breaking complex glucose down into simple CO2 and ribose release or use energy? [Answer: release]
Answer question 15: What example from nature demonstrates this relationship between energy and breaking down molecules? [Answer: When people eat glucose, it is fully formed, but our bodies gain energy by breaking glucose down]
Answer question 16: What is it called when a complex molecule is broken up into more simple molecules? [Answer: catabolism]
Answer question 17: Does building ribose together with other carbons and nitrogens release or use energy? [Answer: use]
Answer question 18: What example from nature demonstrates this relationship between energy and building up molecules? [Answer: Photosynthesis shows that building a sugar requires energy because plants use light energy to build sugars.]
Answer question 19: What is it called when simple molecules are used to build a more complex molecule? [Answer: anabolism]
Answer question 20: Why is both matter and energy needed from glucose to build new biomolecules? [Answer: Because the C and H are needed for some parts of biomolecules (like the ribose of adenylate) and energy is needed to form chemical bonds to build up new molecules via anabolism.]
Possible misconception #1) Ribose looks more complicated than glucose, so going from glucose to ribose must require energy. To correct this, point out how simple CO2 is. Possible misconception #2) Breaking bonds should use/require energy. To correct this, ask the student whether breaking down sugar or building a sugar molecule releases energy. Building a sugar requires energy (plants use light energy to do this) but breaking down a sugar releases energy (our bodies do this to get energy).
Go to slide 17. Students do the Think, Pair, Share, and the teacher ask the students to correct phrases containing misconceptions discussed during the "share" time. The teacher asks the students if they need further clarification on any phrases they have written.
Sample answer for Think:
Think - write a description of adenylate synthesis using the terms matter, carbon, nitrogen, catabolism, anabolism, and energy. [The matter from glucose changes slightly because a carbon is lost, but the rest of the carbons become part of adenylate. The nitrogen has to come from a different source since glucose molecules do not contain nitrogen.]
Go to slide 18. Give the following instructions to students: 1. On a slip of paper, write two misconceptions, questions, or knowledge gaps a student in this class may have about building biomolecules. 2. Select a biomolecule present in marine cryptomonads to find something other than adenylate that can be formed using the glucose hydrocarbon backbone and glycine, urea, and/or purines. 3. In the Biomolecule Builders Activity sheet, prepare a "teacher key" containing the following items:
1 min description of the role of that biomolecule in the human body
explanation of the release of energy from chemical bonds in the catabolism process (specific atoms like C, O, H, N, and P should be mentioned)
explanation of the use of energy in the anabolism process (state the energy source and in what form it was stored).
The teacher will collect the slips of paper with the misconceptions, questions, or knowledge gaps and a basket.
Example misconceptions, questions, or knowledge gaps:
Energy is used in catabolism since it is difficult to break chemical bonds right? [No, energy is released because breaking down sugar is what supplies our bodies with energy]
Our bodies store energy in the form of glucose, so we could survive by eating only glucose. [Energy is only one of the things our body needs. The need for diverse forms of matter (like nitrogen) is not met by glucose intake alone because these molecules contain only carbon and hydrogen and oxygen.]
Light energy the drives anabolism in human cells right? [No, light energy does drive photosynthesis in plants to anabolize CO2 and H2O into sugars, but human cells use chemical energy stored in sugar molecule bonds to drive anabolism. That is why we have to take sugars into our bodies by eating plants.]
What is a hydrocarbon backbone? [It is the chain of C, O, and H in molecules like glucose]
Glucose is made of hundreds of different elements right? [No, only C, O, and H are in glucose]
What types of nitrogen sources can humans take into their systems? [Proteins]
What types of nitrogen sources can organisms like marine cryptomonads take into their systems? [glycine, urea, and purines]
What other types of matter besides nitrogen and hydrocarbons are needed to form amino acids like methionine? [Sulfur and nitrogen and phosphorus]
Why do our bodies synthesize nucleotides? [To make DNA polymers to store genetic information]
What human body processes could not occur if nucleotides were not synthesized in our cells? [Transcription and cell replication and translation]
Why do our bodies synthesize amino acids? [To build proteins]
What human body processes could not occur if amino acids were not synthesized in our cells? [Enzymatic reactions]
Go to slide 19. Give students the following instructions: 1. Draw a slip of paper. 2. write a response to the misconception, knowledge gap, or question. 3. pair up and make a video recording the following:
each give a 1 min presentation of the function of their choice biomolecule
each look at the other's biomolecule, and explain what would have to occur in the catabolism and anabolism process to build that molecule
each look at the teacher key and add an extra detail their partner's catabolism/anabolism explanation
each present the misconception, knowledge gap, or question to the other, give the other a chance to respond, and then help the other completely address it
Evaluate
Students will record the molecule break and build lesson they teach to their partner.
To give opportunity for revision and further mastery of the material, students may write a written explanation to earn back any point lost on the video.
Resources
Anita, N.J. & Chorney, V. (1968), Nature of the Nitrogen Compounds Supporting Phototrophic Growth of the Marine Cryptomonad Hemiselmis virescens *. The Journal of Protozoology, 15: 198-201. doi:10.1111/j.1550-7408.1968.tb02111.x
I Think/We Think https://learn.k20center.ou.edu/strategy/141
Think, Pair, Share https://learn.k20center.ou.edu/strategy/139