Teacher Notes

Target NGSS Standard: HS-LS1-6 Construct and revise an explanation based on evidence for how carbon, hydrogen, and oxygen from sugar molecules may combine with other elements to form amino acids and/or other large carbon-based molecules.

Alignment:

• SEP: Constructing Explanations and Designing Solutions (Students construct an explanation based on valid and reliable evidence from the simulation).
• DCI: LS1.C: Organization for Matter and Energy Flow in Organisms (The process of photosynthesis converts light energy to stored chemical energy by converting carbon dioxide plus water into sugars plus released oxygen. The sugar molecules thus formed contain carbon, hydrogen, and oxygen: their hydrocarbon backbones are used to make amino acids and other carbon-based molecules).
• CCC: Energy and Matter (Changes of energy and matter in a system can be described in terms of energy and matter flows into, out of, and within that system).

Evidence Statements Addressed: Students will demonstrate they can:

1. Construct an explanation detailing the relationship between atoms from sugar molecules and those same atoms found in amino acids and other large carbon-based molecules.
2. Explain that larger carbon-based molecules are a result of chemical reactions between sugar molecules (or their component atoms) and other atoms.
3. Identify and describe evidence from the simulation that all organisms take in matter and rearrange atoms in chemical reactions, and that complex molecules are composed largely of carbon, oxygen, and hydrogen atoms.

Estimated Time: 45-60 minutes Materials: Computer/tablet with internet access, Simulation: Macromolecule Biosynthesis Model, student handout/notebook.

Macromolecule Biosynthesis: How Does a Tree Grow?

Part 1: Engage (Anchoring Phenomenon)

Imagine a giant redwood tree growing hundreds of feet tall. We know that plants “eat” by performing photosynthesis—they take in sunlight, water ($H_2O$), and carbon dioxide ($CO_2$) to produce sugar (Glucose: $C_6H_{12}O_6$) and oxygen ($O_2$).

However, a tree’s massive trunk, its leaves, and its roots are not made of sugar! They are built from complex structural proteins, lipids (fats) for cell membranes, and DNA. If a tree only makes sugar, where does the mass come from to build these complex, non-sugar structures?

Discussion Question: Based on the chemical formula for Glucose ($C_6H_{12}O_6$), what atoms does a plant have available to build with? What happens if a plant needs to build a protein that requires a Nitrogen (N) atom?

Part 2: Explore (Simulation Investigation)

In this activity, you will use the Macromolecule Biosynthesis Model simulation to investigate how a plant converts sugar into other necessary biological molecules.

Instructions:

1. Open the simulation and locate the Source: Glucose section.
2. Click Breakdown Glucose. Observe what happens to the Glucose molecule ($C_6H_{12}O_6$) and note the atoms added to your Available Atoms (Inventory).
3. In the Synthesis Controls section, select Glycerol (Lipid) from the dropdown.
4. Check the “Required Atoms” and compare it to your inventory. If you have enough, click Synthesize Molecule.
5. Select Glycine (Amino Acid) from the dropdown. You will notice you are missing an atom required for proteins.
6. Use the + button next to the Nitrogen (N) inventory to absorb Nitrogen from the simulated soil/environment until you meet the requirement.
7. Click Synthesize Molecule.
8. Repeat the process to synthesize Alanine (Amino Acid). (You may need to breakdown another Glucose molecule to get enough Carbon, Hydrogen, and Oxygen!).

Data Collection: Record the required atoms for each synthesized molecule in the table below.

Part 3: Explain (Sensemaking)

Using the data you collected from the simulation, answer the following questions:

1. Matter Transfer: When you broke down the Glucose molecule, what three types of atoms became available in your inventory? _____

2. Synthesis Source: Look at your data for Glycerol (a lipid). Did you need to absorb any extra atoms from the environment to build it, or did all the atoms come directly from the Glucose? _____

3. Building Proteins: Look at your data for the Amino Acids (Glycine and Alanine). What specific atom had to be absorbed from the environment (soil) to successfully build them? Why couldn’t the plant build them using only the atoms from Glucose? _____

Part 4: Elaborate/Evaluate (Argumentation & Modeling)

Student Deliverable: Scientific Explanation

Construct a scientific explanation to answer our original question: How does a tree get the mass to build complex structures like proteins and cell membranes if it only produces sugar during photosynthesis?

Your explanation MUST include the following evidence and reasoning:

• State the types of atoms found in sugar (glucose).
• Explain how the atoms in sugar are used as the “building blocks” (hydrocarbon backbone) for other molecules.
• Describe where the plant must obtain elements (like Nitrogen) that are not found in sugar.
• State clearly that chemical reactions rearrange these atoms to form new, larger products.

Extension Option: If a disease destroyed a plant’s roots so it could no longer absorb nitrogen from the soil, which type of macromolecule (Lipid or Amino Acid) would the plant stop being able to produce first? Explain your reasoning.