Week 6 Biology Lab & Inquiry: Yeast Fermentation, Feeding the CO₂ Factory

Part 1 — The Big Picture

This week you followed glucose through four stages and met fermentation, the backup a cell uses when oxygen runs out. In this lab you put that backup to work in your kitchen. Yeast in a sealed bottle of sugar water run short of oxygen and ferment the sugar, giving off carbon dioxide that inflates a balloon. You run it as a controlled test with four bottles and one changed variable, the sugar, and a no-sugar bottle as the control. You measure each balloon, work out how much each extra teaspoon adds, and read the shape of the trend. Then you contrast what fermentation pays the yeast with what the full aerobic pathway pays, and you check a chatbot's account of your lab and catch where it puts a stage in the wrong place, names the wrong gas, or invents a number.

Time budget: Plan for about 120 minutes.

Part 2 — The Task

Guiding question: How does the amount of sugar change how much carbon dioxide yeast make by fermentation, and does each extra teaspoon add as much gas as the one before?

Before you begin — hypothesis: Before you add any sugar, write your hypothesis in the if… then… because… form: if more sugar is added to the yeast, then the balloon will be larger or smaller at 30 minutes, because of a reason about fermentation you can state. Then predict whether each extra teaspoon will add the same amount of gas, more, or less.

Workshop data: Your own four-bottle yeast measurements and the illustrative fallback measurements

Source: Balloon circumferences you measure yourself at a kitchen counter with the procedure in Part 3; if you cannot run the bottles, use the illustrative fallback measurements, which were constructed for this lab and are not real data.

• Rows: 4 bottles measured (0, 1, 2, and 4 teaspoons of sugar), shown as 4 rows of the measurement table; the first scaffold table has 6 rows that name the parts of the test rather than data, and the contrast table has 4 rows
• Columns: bottle, circumference at 30 minutes in cm, and increment from the bottle before in cm
• Fallback measurements: 4 illustrative circumferences constructed for this lab, used only if you cannot run your own bottles

Part 3 — Materials & Procedure

Tools and materials

• Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet)
• Four clean, identical plastic bottles, four balloons, dry yeast, sugar, a measuring teaspoon, warm tap water, a piece of string, and a ruler
• A document or notebook for your written answers

Ways of working

• virtual-simulation-inquiry
• at-home-protocol-and-data-table
• figure-and-diagram-interpretation

Procedure

1. Gather four clean, identical plastic bottles, four balloons, a packet of dry yeast, sugar, a measuring teaspoon, warm tap water, a piece of string, and a ruler. Stretch each balloon a few times so it inflates easily. Open a blank spreadsheet and a document for your answers. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: All materials on the counter, four stretched balloons, a blank spreadsheet, and an open document.
2. Before mixing anything, write your hypothesis and prediction in the first table in Part 4, and name the independent variable, the dependent variable, at least two controlled variables, and the control group. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: The first table has an if… then… because… hypothesis and every part of the test named.
3. Label the bottles 0, 1, 2, and 4. Pour the same amount of warm tap water, about one cup, into each bottle and add one level teaspoon of dry yeast to each. Add 0, 1, 2, and 4 level teaspoons of sugar to the matching bottles. Cap each bottle with your thumb and swirl it for a few seconds. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: Four bottles with the same water and the same yeast, differing only in sugar.
4. Stretch a balloon over the mouth of each bottle right away, set all four bottles side by side in the same warm spot, and start a 30-minute timer. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: Four sealed bottles waiting in the same place for the same time.
5. At 30 minutes, wrap the string once around the widest part of each balloon, pinch where it meets, and lay the string along the ruler. Record each circumference in centimeters in the measurement table, starting with the 0-teaspoon control. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: Four circumferences recorded in centimeters, with the control measured the same way as the others.
6. In the spreadsheet, type the teaspoons 0, 1, 2, and 4 into cells A2 to A5 and your circumferences into B2 to B5. Subtract each reading from the one after it by hand first, then type =B3-B2 into C3 and copy it down to C5 to check your increments. Select columns A and B and insert a chart to see the trend. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: Each spreadsheet increment in C3 to C5 matches your hand subtraction, and the chart shows how the circumference changes with sugar.
7. Optional virtual check: open the HHMI BioInteractive site and search for an animation on cellular respiration or fermentation to compare its stage order with this week's chapter. Then fill in the contrast table, answer the analysis questions, paste your completed tables into an approved chatbot with the prompt in Part 6, and check its reply against the scripted checks. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: A completed contrast table, written answers, and a list of the chatbot's errors with corrections.

Fallback route

When to use it: Use this route if you cannot get bottles, balloons, yeast, or sugar, or if you cannot run the bottles at home.

Use the illustrative fallback measurements below, constructed for this lab and not real data, as your measurement table, then complete every scaffold table, analysis question, and the critique step from them and submit the same items for equal credit.

This route earns the same credit as the primary route.

Four illustrative fallback circumferences at 30 minutes, constructed for this lab, that stand in for your own bottles.

Fallback model data

Bottle	Circumference at 30 minutes (cm)	Increment from the bottle before (cm)
0 teaspoons (control)	0
1 teaspoon	6
2 teaspoons	11
4 teaspoons	15

Part 4 — The Scaffold

Name every part of the test before you add any sugar, so the comparison is fair from the first bottle.

Student scaffold table 1

Part of the test	Your answer
Hypothesis (if… then… because…)
Prediction: will each extra teaspoon add the same gas, more, or less?
Independent variable
Dependent variable
Controlled variables (at least two)
Control group and why it is there

Record each balloon's circumference at 30 minutes, then subtract each reading from the one after it to find the increment.

Student scaffold table 2

Bottle	Circumference at 30 minutes (cm)	Increment from the bottle before (cm)
0 teaspoons (control)		none, this is the first bottle
1 teaspoon
2 teaspoons
4 teaspoons

Contrast what your yeast did in a sealed bottle with what the full aerobic pathway does, using this week's chapter.

Student scaffold table 3

Feature	Aerobic cellular respiration	Alcoholic fermentation in your bottles
Is oxygen needed?
Stages that run, in order, with their places
What pyruvate becomes
ATP per glucose, in words

Part 5 — Analysis Questions

1. Using your measurement table, write out each increment as a subtraction with its units. Which teaspoon added the most gas, and how much did going from 2 to 4 teaspoons add compared with the first teaspoon?
2. Describe in words how the circumference changed as sugar increased. Did it always rise, did the gains shrink, and what did the 0-teaspoon bottle do?
3. Name the gas in the balloons and the process that made it, explain why the 0-teaspoon bottle belongs in the test, and say whether your evidence supports or fails to support your hypothesis.
4. Using your contrast table, explain why yeast in a sealed bottle ferment, compare the 2 ATP per glucose of fermentation with the full pathway's about 30 to 32, and connect the yeast to a sprinting muscle that runs short of oxygen.
5. Choose one and answer it in 3–4 sentences. (a) Measuring a balloon with a string is a source of error; name one way it could mislead you and one change that would make your measurements more reliable. (b) Your numbers will not match another student's; explain what you can and cannot claim from one run of four bottles.

Part 6 — AI-Critique Moment

Choose one equal-credit critique route. Route A: ask an approved AI tool to critique your completed work, then check its response against your own evidence. Route B is the no-AI equivalent printed below.

Approved tools: Claude, Gemini, ChatGPT, Grok, Microsoft Copilot.

Prompt to paste:

I've pasted my completed Week 6 Biology Lab & Inquiry tables above. I set up four bottles with the same yeast and warm water and 0, 1, 2, and 4 teaspoons of sugar, covered each with a balloon, measured each balloon's circumference at 30 minutes, and worked out the increment from each bottle to the next. Please do seven things. First, list the four stages of cellular respiration in order and name the place in the cell where each one runs. Second, name the gas that filled my balloons and the process that made it. Third, check the increments in my circumference table, showing each subtraction. Fourth, describe a mitochondrion with its parts labeled and say which part carries the electron transport chain and which runs the citric acid cycle. Fifth, compare how much ATP per glucose my yeast got from fermentation with what the full aerobic pathway gives. Sixth, tell me the exact circumference a balloon should reach at 30 minutes with 2 teaspoons of sugar, with its source. Seventh, as a stretch question for later in the course, say how many cells a body cell makes when it divides for growth, and what phenotype ratio a cross of two Tt parents gives.

Test the response for these likely failures:

• Chatbots often list the citric acid cycle before glycolysis, drop pyruvate oxidation, or place the citric acid cycle in the cytoplasm beside glycolysis.
• Chatbots sometimes put the electron transport chain in the fluid matrix or on the smooth outer membrane, and the citric acid cycle on a membrane.
• Chatbots often say the balloons filled with oxygen, or that fermentation is a high-energy shortcut that gives yeast as much ATP as respiration.
• Chatbots often state an exact expected circumference for a 2-teaspoon balloon, or cite a study or a percentage that was never given.
• Chatbots sometimes say a body cell dividing for growth makes four cells, which is meiosis, not mitosis.
• Chatbots often give the phenotype ratio of a Tt × Tt cross as 1:2:1, which is the genotype ratio.

In 3–5 sentences, name what the chatbot got right, quote at least two errors, and correct each with evidence from your own tables or this week's chapter; mark the two stretch answers as things to check in later weeks.

Equivalent route (no AI required)

No AI account is required for this lab. Instead of the chatbot, critique this flawed analysis, printed here in full: "My four balloons filled with oxygen that the yeast breathed out, because yeast make energy from sugar. Fermentation gave my yeast lots of ATP, about as much as aerobic respiration, which is why the balloons grew so fast. In cellular respiration the citric acid cycle comes first, in the cytoplasm, and glycolysis comes last, in the mitochondrion. The electron transport chain floats in the fluid matrix. A 2-teaspoon balloon should reach exactly 13.7 cm at 30 minutes, according to a study. As a preview of later weeks, a body cell dividing for growth makes four identical cells, and a cross of two Tt parents gives a 1:2:1 phenotype ratio." Mark it up: quote each flawed sentence, name what is wrong (a stage out of order, a mislabeled structure, an over-simplified mechanism, an invented figure, or a preview fact stated wrong), cite the evidence from your tables or this week's chapter, and write a corrected sentence beneath it; for the two preview sentences, say which later week will check them. This route assesses the same objectives (Objective 1 and Objective 4) as the chatbot critique, takes comparable effort (about 30 minutes and 200–300 words), is scored by the same scoring criteria for the same credit, and its own submission artifact is the marked-up flawed analysis, posted in place of the chatbot share link and report.

Part 7 — What to Submit

• All three completed scaffold tables, filled from your own bottles or the illustrative fallback measurements
• Written answers to all five analysis questions
• The chatbot critique report with its share link, or the equivalent route's marked-up flawed analysis

Deliverable:

A short Biology Lab & Inquiry report on yeast fermentation: three completed tables (the named parts of the test, four bottles with circumferences and increments, and the aerobic-versus-fermentation contrast), written answers to five analysis questions, and a critique of a chatbot's account of your lab, or, on the equivalent route, a marked-up correction of the printed flawed analysis. 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. Choose a written, recorded, or visual form for your answers; every form is graded by the same scoring criteria.

Rubric

The rubric below shows how each submitted part is evaluated; bands are full, partial, or none.

Workshop evaluation criteria

Criterion	Full	Partial	None
Testable hypothesis and the parts of the test	A falsifiable if… then… because… hypothesis and a prediction about the gains appear before sugar is added, and the independent variable, dependent variable, at least two controlled variables, and the 0-teaspoon control group are each named correctly.	A hypothesis appears but is not falsifiable or lacks a prediction, or one or two parts of the test are missing or swapped.	No hypothesis, or the parts of the test are not named.
Measurement table and increment arithmetic	All four circumferences come from the student's own bottles or the fallback measurements, in centimeters, and all three increments are correct subtractions with units.	The table is filled, but one increment is miscalculated, a unit is missing, or a reading is subtracted in the wrong direction.	No measurements are recorded, or the readings are invented rather than measured or taken from the fallback.
Contrast of aerobic respiration and fermentation	The contrast table is complete and accurate: oxygen needed only for the aerobic pathway, the four stages in order with their places, pyruvate becoming ethanol and carbon dioxide in the bottles, and 2 ATP per glucose against about 30 to 32 stated in words.	The table is attempted, but one or two cells misplace a stage, name the wrong product, or treat fermentation as a high-ATP process.	The contrast table is missing or does not address the two pathways.
Analysis in words	Questions 1 to 4 are answered accurately: the increments compared, the rising trend with shrinking gains described, the gas named as carbon dioxide from alcoholic fermentation with the control's role explained and supports or fails to support used, and the yeast connected to a muscle short of oxygen.	The questions are attempted, but one or two answers call the gas oxygen, skip the control's role, or claim the evidence proves the hypothesis.	The analysis questions are missing or do not address the measurements.
Critique of the chatbot or of the printed flawed analysis	On either route, at least two errors are quoted and corrected with evidence from the student's own tables or the chapter, the two stretch answers are marked to check later, and one correct point is acknowledged; both routes earn this band equally.	On either route, errors are named but corrected without evidence, or only one error is caught.	No critique appears, or pasted output is submitted without any checking.
Reflection on the limits of the test	The chosen reflection option is answered in 3–4 sentences that tie a specific source of error or limit to a concrete change in the test or in what can be claimed.	The reflection is answered but stays general or names no specific change.	No reflection is submitted.

Quality Gate

• Every circumference in the measurement table comes from your own bottles or the printed fallback measurements, never from memory or a chatbot.
• Every increment is written as a subtraction of a reading from the one after it, with units.
• The hypothesis was written before any sugar was added and has the if… then… because… form.
• The independent variable, dependent variable, controlled variables, and the 0-teaspoon control group are each named.
• The stages in the contrast table are in order and each is placed in its part of the cell.
• No circumference, ATP count, study, or source is invented anywhere in the submission.
• The critique quotes the chatbot or the flawed analysis and corrects at least two errors with evidence from your tables or the chapter.