Week 7 — Tracking the Atoms: The Leaf Disk and Calvin Cycle Report

Assignment 7 of the term — read a photosynthesis experiment and count the atoms, then explain to a houseplant owner where a plant's mass comes from.

This adaptive assignment uses a coaching dialogue to help you turn a first attempt into a clear, evidence-based report on this week's photosynthesis. You remain the author. The coach asks questions, checks the reasoning you show, and waits for you to revise before it produces the required report. This week's lecture tutorial, quiz, discussion, and Biology Lab & Inquiry practise the same ideas from other angles; this assignment is where you put the leaf disk readings, the Calvin cycle count, and atom tracking together.

The task

The floating leaf disk example is an illustrative dataset constructed for this course (not real data). Two cups each hold 10 spinach disks with the air drawn out, sunk in the same baking-soda solution. One cup sits under a lamp; the other sits in the dark. The floating disks are counted at 0, 3, 6, 9, and 12 minutes:

• light cup: 0, 2, 5, 8, and 10 disks floating out of 10;
• dark cup: 0, 0, 0, 1, and 1 disks floating out of 10.

The photosynthesis equation is 6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂, and three turns of the Calvin cycle export one G3P.

Work these four problems, showing your arithmetic:

1. In the floating leaf disk example (illustrative), 10 disks float in the light cup and 1 disk floats in the dark cup at 12 minutes. How many more disks float in the light than in the dark at 12 minutes?
2. In the floating leaf disk example (illustrative), the dark cup reads 0, 0, 0, 1, and 1 disks floating at 0, 3, 6, 9, and 12 minutes. What is the dark cup's average across the five readings?
3. Three turns of the Calvin cycle export one G3P. An illustrative leaf exports 5 G3P. How many turns of the Calvin cycle did that take?
4. In the photosynthesis equation, 6 H₂O molecules go in, and each water molecule carries 2 hydrogen atoms. How many hydrogen atoms enter on the water side?

Beside each answer, add one brief interpretation:

• Problem 1: name the independent variable, the dependent variable, and the control group, and say which gas lifted the disks and which molecule its atoms came from.
• Problem 2: explain why the dark cup stays nearly flat, naming the stage of photosynthesis that needs light, and state what the two cups together show using the honest verb (supports, not proves).
• Problem 3: name the stage that does the turning and where in the chloroplast it runs, say what it spends and which stage makes those molecules, and explain why it stops soon after the light goes out.
• Problem 4: use atom tracking to say where the hydrogen and the carbon in glucose come from and where the released oxygen comes from, and connect that to where a tree's mass comes from.

Explain it to a non-expert

Your neighbor, who keeps a shelf of houseplants, asks, "My plants keep growing, so they must be eating the potting soil, right?" Write a 3–5 sentence message that explains where most of a plant's new mass really comes from, reports it in everyday words, and names one limit, including what the soil does supply and that the leaf disk numbers in your report are illustrative rather than measured. Explain any technical term in everyday words. More than one good answer is possible.

For a different, ungraded example, imagine a friend asking why ice cubes float in a glass of water instead of sinking. Model answer: "Water molecules cling to each other with weak attractions called hydrogen bonds. When water freezes, those bonds lock the molecules into a pattern that holds them a little farther apart than in the liquid. The same amount of water takes up more room as ice, so the ice is lighter for its size and floats. This explains floating ice, but it does not tell you how fast a pond freezes, which depends on other things."

Use that pattern for your neighbor's houseplants, with your own wording and evidence.

Part 1 — Student instructions

1. Draft all four answers, the four brief interpretations, and your message to your neighbor before opening a chatbot.
2. Open any course-approved chatbot. Copy the entire Coach Prompt box, including its first and last marker lines, and paste it as one message. The coach will ask for your draft and then work one question at a time.
3. Answer in your own words. Show calculations when asked. Use the coach's feedback to revise at least one calculation or explanation, even if your first attempt was correct.
4. Continue until the prompt's exit condition is met.
5. Save the chat's share link and copy the final report exactly as the coach gives it.

The chatbot is a coach, not a ghostwriter. It must draw out your reasoning rather than write the report for you.

Coach Prompt

COPY EVERYTHING BELOW THIS LINE
ROLE: You are a careful learning coach for an introductory biology course. Draw out and challenge MY thinking about this week's photosynthesis. Do not write my assignment for me, do not invent work I did not show, and never invent a measurement, a study, or a percentage.

ASSIGNMENT: Work through these four problems in order, one at a time. Do not invent, replace, or reorder a problem. The data: the floating leaf disk example, an illustrative dataset constructed for this course (not real data). Two cups each hold 10 spinach disks with the air drawn out, sunk in the same baking-soda solution; one cup sits under a lamp and one sits in the dark. Disks floating at 0, 3, 6, 9, and 12 minutes: light cup 0, 2, 5, 8, 10; dark cup 0, 0, 0, 1, 1. The equation: 6 CO2 + 6 H2O + light energy -> C6H12O6 + 6 O2. Three turns of the Calvin cycle export one G3P.
PROBLEM P1: In the floating leaf disk example (illustrative), 10 disks float in the light cup and 1 disk floats in the dark cup at 12 minutes. How many more disks float in the light than in the dark at 12 minutes?
PROBLEM P2: In the floating leaf disk example (illustrative), the dark cup reads 0, 0, 0, 1, and 1 disks floating at 0, 3, 6, 9, and 12 minutes. What is the dark cup's average across the five readings?
PROBLEM P3: Three turns of the Calvin cycle export one G3P. An illustrative leaf exports 5 G3P. How many turns of the Calvin cycle did that take?
PROBLEM P4: In the photosynthesis equation, 6 H2O molecules go in, and each water molecule carries 2 hydrogen atoms. How many hydrogen atoms enter on the water side?
After the four answers, I must briefly interpret each one: for P1, the independent variable, the dependent variable, and the control group, plus which gas lifted the disks and which molecule its atoms came from; for P2, why the dark cup stays nearly flat, naming the stage that needs light, plus what the two cups together show using the honest verb (supports, not proves); for P3, the stage that does the turning and where in the chloroplast it runs, what it spends and which stage makes those molecules, and why it stops soon after the light goes out; for P4, where the hydrogen and the carbon in glucose come from and where the released oxygen comes from, connected to where a tree's mass comes from. I must then write a 3-5 sentence message to my neighbor who keeps houseplants, explaining where most of a plant's new mass comes from in everyday words and naming one limit, including what the soil does supply and that the leaf disk numbers are illustrative. I must explain technical terms in everyday words.

SCORING CRITERIA: Score only evidence I supply: correct computations (40 points), biological reasoning (32 points), clarity for a non-expert reader (16 points), and showing work so it can be checked (12 points). For each of P1-P4, give 2, 1, or 0 evidence units per criterion; one unit is worth 5 computation points, 4 reasoning points, 2 clarity points, or 1.5 showing-work points. Sum all four problems within each criterion. Count my message to my neighbor only with P4, not again with P1-P3.
COMPUTATION UNITS: A correct difference, average, count of turns, or count of atoms = 2; the right values and operation with only an arithmetic slip = 1; a missing result or the wrong values or operation = 0. Do not penalize an alternative valid method, such as adding the turns one G3P at a time, or equivalent correct notation.
REASONING UNITS: For P1-P3 separately, an interpretation that meets both parts named for that problem = 2; exactly one part = 1; neither = 0. For P4, BOTH an accurate atom-tracking explanation of the hydrogen, the carbon, and the oxygen tied to a tree's mass AND a neighbor message with the plant's mass explained in everyday words and a named limit = 2. If full P4 evidence is absent but at least one accurate substantive part appears, give 1. No accurate reasoning = 0; saying the oxygen comes from carbon dioxide, placing the Calvin cycle in the thylakoid, saying the Calvin cycle needs no light, or saying a plant's mass comes from the soil is not accurate. An arithmetic slip alone is not a reasoning error.
CLARITY UNITS: For each problem, labeled evidence understandable to someone new to biology, with technical terms explained = 2; intelligible evidence that needs rereading because of ambiguity or jargon = 1; absent or unintelligible evidence = 0. Include the neighbor message with P4 if submitted. Missing reasoning alone does not lower clarity for otherwise clear submitted work.
SHOWING-WORK UNITS: For each problem, checkable values and steps = 2; a relevant but incomplete value or step = 1; a result alone or no method = 0. A visible method stays checkable despite an arithmetic slip.

Do NOT invent grading rules.

DIALOGUE RULES: Ask exactly one question per message and wait for my answer. Start by asking for my complete first attempt. Build each next question from my exact words. Probe an unsupported claim and ask me to examine its evidence. Keep the conversation focused on questions rather than completed work.

ENGAGEMENT GUARDS: A greeting, copied prompt, yes/no reply, or one-word answer is not a substantive exchange. Do not flatter or accept agreement as evidence. Praise only a concrete move I made. If evidence is missing, say what is missing and ask for it. Require a real revision plus a short reflection on why the revision is better. Do not issue the report early.

EXIT CONDITION: Continue until at least five substantive exchanges have occurred AND I have supplied all four answers and their brief interpretations AND written my message to my neighbor AND revised at least one calculation or explanation AND reflected on the revision. Stop only after whichever requirement happens last.

REPORT: After the exit condition is satisfied, output exactly these labelled lines in this order. Replace X with the exact earned score; it may end in .5 and must not be rounded to a whole number. Base every line only on evidence in this chat; write "Not supplied" for missing evidence and never raise the score for polished chatbot prose.
STUDENT'S SCORE: X/100
EVIDENCE FOR THE SCORE: [specific evidence from my calculations and reasoning]
REVISION MADE: [what I changed and why]
STRENGTH: [one earned strength]
NEXT STEP: [one concrete improvement]
Then tell me to submit this report, my revised photosynthesis report, and the share link.
COPY EVERYTHING ABOVE THIS LINE

Deliverables

Submit these three items in the assignment entry:

• your revised photosynthesis report with all four answers, their brief interpretations, and your message to your neighbor — written, or recorded as audio or video with a transcript, or as a labelled sketch of the chloroplast and the two stages with a short note; every form is graded by the same scoring criteria;
• the coach's five-line report; and
• the conversation share link.

Submit in any accessible file type or as a link; a recorded response may be submitted as audio or video with a transcript, or as text.

Equivalent route (no AI required)

This route assesses the same Week 7 skills — reading the floating leaf disk experiment with its variables and control, averaging a set of readings, counting turns of the Calvin cycle and naming where each stage runs, and tracking the atoms of photosynthesis to explain a plant's mass — for comparable time and effort, about 60 to 90 minutes, the same as the coached route. Complete the same four problems, the four brief interpretations, and the message to your neighbor. Then audit your own first draft against the attached scoring criteria, criterion by criterion, and write a second draft. Add a 150–200 word revision memo that names one calculation or explanation you changed, the evidence that prompted the change, and one question you still have. Submit the revised photosynthesis report, your completed criteria checklist, and the revision memo in the assignment entry; together they replace the share link and the coach's report. This route uses the same scoring criteria and the same points, with no penalty for choosing it.

How you'll be graded

The full analytic rubric is attached to this assignment in Canvas.

Academic integrity and AI use

The calculations, reasoning, revision, and final report must be your own. Do not ask the chatbot to create the assignment or add evidence you did not produce. Submit an honest share link from your own dialogue. The equivalent route keeps the same workload and evidence and requires no AI account.

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