Week 6 — Feeding the CO₂ Factory: The Yeast and Respiration Report

Assignment 6 of the term — compute what yeast fermentation and cellular respiration produce, and explain to someone new to biology why more sugar does not mean twice the rise.

This adaptive assignment uses a coaching dialogue to help you turn a first attempt into a clear, evidence-based report on fermentation and cellular respiration. 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 yeast balloons, glycolysis, and the four stages together. It builds on Week 5, where you met ATP as the cell's energy currency.

The task

The yeast balloon example is an illustrative dataset constructed for this course (not real data). Four bottles hold the same amount of yeast in the same warm water with 0, 1, 2, and 4 teaspoons of sugar, and a balloon covers each opening. At 30 minutes the balloon circumferences are 0, 8, 14, and 18 cm. The gas is carbon dioxide from alcoholic fermentation, pyruvate → ethanol + CO₂, which yields only glycolysis's 2 ATP per glucose. In the full aerobic pathway, glycolysis splits each glucose into 2 pyruvate in the cytoplasm, and the complete breakdown releases 6 CO₂ per glucose: 2 in pyruvate oxidation and 4 in the citric acid cycle in the mitochondrial matrix.

Work these four problems, showing your arithmetic:

1. In the yeast balloon example, the 1-teaspoon balloon reads 8 cm and the 2-teaspoon balloon reads 14 cm at 30 minutes. How many centimeters of circumference does the second teaspoon add?
2. A model muscle cell runs glycolysis on 3 glucose molecules, and each glucose splits into 2 pyruvate. How many pyruvate molecules does the cell make?
3. Each glucose that is fully broken down releases 6 CO₂ molecules: 2 in pyruvate oxidation and 4 in the citric acid cycle. How many CO₂ molecules are released when 4 glucose molecules are fully broken down?
4. In the yeast balloon example, the first teaspoon of sugar adds 8 cm of circumference, and going from 2 to 4 teaspoons adds 4 cm. How many times larger is the first gain than the last?

Beside each answer, add one brief interpretation:

• Problem 1: explain what the 0-teaspoon control shows, and name the gas and the process that made it.
• Problem 2: say where in the cell glycolysis runs, and explain why it can keep running when oxygen runs short.
• Problem 3: say where in the cell that carbon dioxide is released, and where it goes after it leaves the cell.
• Problem 4: explain why the gains shrink as sugar is added, and use your neighbor message (below) to compare fermentation's payoff with the full pathway's.

Explain it to a non-expert

A neighbor who bakes bread most weekends asks, "If I double the sugar, will my dough rise twice as much?" Write a 3–5 sentence message that answers in everyday words using your results, compares fermentation's 2 ATP per glucose with the full pathway's about 30 to 32, and names one limit of the evidence, including that the yeast balloon numbers are an illustrative model and that real yeast and kitchens vary. Explain any technical term in everyday words. More than one good answer is possible.

For a different, ungraded example, imagine a café owner asking why hiring a third cashier helped less than hiring the second, using made-up numbers from one afternoon. Model answer: "A new cashier helps only when customers are waiting. The second cashier cleared a long line, so the gain was big; by the time the third started, the line was already short, so there was less left to gain. That is why each added cashier helped less than the one before. My numbers come from one made-up afternoon, so a busier day could look different."

Use that pattern for the bread question, 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 cellular respiration and fermentation. 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 yeast balloon example, an illustrative dataset constructed for this course (not real data). Four bottles hold the same amount of yeast in the same warm water with 0, 1, 2, and 4 teaspoons of sugar; at 30 minutes the balloon circumferences are 0, 8, 14, and 18 cm. The gas is CO2 from alcoholic fermentation (pyruvate -> ethanol + CO2), which yields only glycolysis's 2 ATP per glucose. In the full aerobic pathway, glycolysis splits each glucose into 2 pyruvate in the cytoplasm, and the complete breakdown releases 6 CO2 per glucose: 2 in pyruvate oxidation and 4 in the citric acid cycle in the mitochondrial matrix.
PROBLEM P1: In the yeast balloon example, the 1-teaspoon balloon reads 8 cm and the 2-teaspoon balloon reads 14 cm at 30 minutes. How many centimeters of circumference does the second teaspoon add?
PROBLEM P2: A model muscle cell runs glycolysis on 3 glucose molecules, and each glucose splits into 2 pyruvate. How many pyruvate molecules does the cell make?
PROBLEM P3: Each glucose that is fully broken down releases 6 CO₂ molecules: 2 in pyruvate oxidation and 4 in the citric acid cycle. How many CO₂ molecules are released when 4 glucose molecules are fully broken down?
PROBLEM P4: In the yeast balloon example, the first teaspoon of sugar adds 8 cm of circumference, and going from 2 to 4 teaspoons adds 4 cm. How many times larger is the first gain than the last?
After the four answers, I must briefly interpret each one: for P1, what the 0-teaspoon control shows, and the gas and the process that made it; for P2, where in the cell glycolysis runs, and why it can keep running when oxygen runs short; for P3, where in the cell that carbon dioxide is released, and where it goes after it leaves the cell; for P4, why the gains shrink as sugar is added. I must then write a 3-5 sentence message to a neighbor who bakes bread, answering in everyday words whether doubling the sugar doubles the rise, using my results, comparing fermentation's 2 ATP per glucose with the full pathway's about 30 to 32, and naming one limit, including that the yeast balloon numbers are an illustrative model. 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 increment, pyruvate count, carbon dioxide count, or gain comparison = 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 or equivalent notation, such as writing the comparison as 2 times or as 8:4 reduced to 2:1.
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 explanation of the shrinking gains AND a neighbor message that compares the two ATP payoffs and names a limit = 2. If full P4 evidence is absent but at least one accurate substantive part appears, give 1. No accurate reasoning = 0; calling the gas oxygen, placing glycolysis or the citric acid cycle in the wrong compartment, saying glycolysis needs oxygen, or calling fermentation a high-ATP process 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 yeast and respiration report, and the share link.
COPY EVERYTHING ABOVE THIS LINE

Deliverables

Submit these three items in the assignment entry:

• your revised yeast and respiration 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 four bottles 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 6 skills — computing an increment from the yeast balloon example, counting what glycolysis and the full pathway produce, placing each stage in its part of the cell, and explaining fermentation as a low-ATP backup — 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 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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