Week 3 Biology Lab & Inquiry: Testing for Macromolecules in Food

Part 1 — The Big Picture

This week you learned that structure determines function: a molecule's shape decides the job it can do. In this lab you see that rule at a kitchen counter. Iodine solution is amber, an orange-brown color, and it turns blue-black only when it can fit inside the coiled chain of starch. You write a hypothesis before you start, test five foods against a plain-water negative control, record a color call for each, and explain every result from the shape of the molecules in the food. Then you check a chatbot's account of your lab and catch where it oversimplifies the test, mislabels a molecule, scrambles an order, or invents a number.

Time budget: Plan for about 120 minutes.

Part 2 — The Task

Guiding question: Which of five kitchen foods contain starch, and how does the shape of each food's molecules explain the color iodine shows?

Before you begin — hypothesis: Before you add a single drop of iodine, write one hypothesis in the if… then… because… form for the sugar water or the bread: if iodine is added to that food, then it will turn blue-black or stay amber, because of a reason about the food's molecules that you can state. Then write a prediction (starch present or absent) for every food in the data table.

Workshop data: Your own iodine color calls, or the illustrative fallback color calls

Source: Six color calls you record yourself at a kitchen counter with the procedure in Part 3; if you cannot run the protocol, use the six illustrative fallback color calls printed in the fallback, which were constructed for this lab and are not real data.

• Rows: 6 samples, 5 foods and 1 plain-water negative control, shown as 6 rows of the data table; the first scaffold table has 5 rows that name the parts of the test rather than data
• Columns: sample, the class of macromolecule you predict, the iodine color you see, the starch call, and the structure reason
• Unit: a color call described in words: amber (orange-brown, the color with no starch), blue-black, or a faint change

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)
• Iodine solution, a dropper or a drinking straw, six small saucers or a plate, a spoon, a cup of tap water, and five foods: a piece of bread, a slice of raw potato, a spoonful of sugar water, a spoonful of cooking oil, and a slice of fruit
• 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. As a precaution, cover the counter with a paper towel, wear old clothes, keep the iodine away from mouths, eyes, and pets, and do not eat any tested sample; throw each one away afterward. Set six saucers in a row and label them plain water, bread, potato, sugar water, oil, and fruit. Tool: Iodine solution, a dropper or a drinking straw, six small saucers or a plate, a spoon, a cup of tap water, and five foods: a piece of bread, a slice of raw potato, a spoonful of sugar water, a spoonful of cooking oil, and a slice of fruit. Check: Six labeled saucers on a protected counter.
2. Before any iodine goes on a sample, write your hypothesis and your predictions in the first table in Part 4, and name the negative control and the one thing you will keep the same for every sample. Tool: A document or notebook for your written answers. Check: The first table has a hypothesis in if… then… because… form, a prediction for every food, and plain water named as the negative control.
3. Put a spoonful of plain water on the first saucer and add 2 drops of iodine solution. Note its color in words. This is the color a no result should give. Tool: Iodine solution, a dropper or a drinking straw, six small saucers or a plate, a spoon, a cup of tap water, and five foods: a piece of bread, a slice of raw potato, a spoonful of sugar water, a spoonful of cooking oil, and a slice of fruit. Check: The plain-water control stays amber, an orange-brown color.
4. Put a small piece of each food on its own saucer and add the same 2 drops of iodine to each one. Wait about a minute, then record the color in words beside the control's color: blue-black, still amber, or a faint change. If telling colors apart is hard for you, judge darkness instead: starch makes the spot nearly black, far darker than the control, or ask someone to confirm your call. Tool: Iodine solution, a dropper or a drinking straw, six small saucers or a plate, a spoon, a cup of tap water, and five foods: a piece of bread, a slice of raw potato, a spoonful of sugar water, a spoonful of cooking oil, and a slice of fruit. Check: A color call in words for every food, each compared with the plain-water control.
5. Open a blank sheet. Type the six sample names into cells A2 to A7 and your starch calls (present, absent, or little) into B2 to B7. In D2 type =COUNTIF(B2:B7,"present"), in D3 type =COUNTIF(B2:B7,"absent"), and in D4 type =COUNTIF(B2:B7,"little"). 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 three counts in D2, D3, and D4 add up to 6, the number of samples you tested.
6. Complete the reasoning table, answer the analysis questions in your document, then paste your completed tables into an approved chatbot with the prompt in Part 6 and check its answer against the scripted checks. Tool: A document or notebook for your written answers. Check: Completed tables, 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 iodine solution or the foods, or if you cannot run the test at home.

Use the six illustrative fallback color calls below, constructed for this lab and not real data, as your data table, then complete every scaffold table, analysis question, and the critique step from them and submit the same items for equal credit. Fill the empty columns yourself.

This route earns the same credit as the primary route.

Six illustrative fallback color calls, constructed for this lab, that stand in for your own samples.

Fallback model data

Sample	Class of macromolecule you predict	Iodine color, in words	Starch call (present, absent, or little)	Structure reason in one phrase
Plain water (negative control)		stays amber
Cracker		turns blue-black
Cooked pasta		turns blue-black
Cheese		stays amber
Sugar-cube water		stays amber
Apple slice		stays amber with a faint darkening

Part 4 — The Scaffold

Name every part of the test before the first drop of iodine, so the comparison is fair from the start.

Student scaffold table 1

Part of the test	Your answer
Hypothesis (if… then… because…)
Negative control and why it is the baseline
What you change from saucer to saucer
What you observe and record
One thing you keep the same for every sample

Record each sample as you go, comparing every color with the plain-water control.

Student scaffold table 2

Sample	Class of macromolecule you predict	Iodine color, in words	Starch call (present, absent, or little)	Structure reason in one phrase
Plain water (negative control)
Bread
Raw potato
Sugar water
Cooking oil
Fruit

Explain the two results that surprise people most, from the shape of the molecules.

Student scaffold table 3

Question	Your reasoning
Why does sugar water stay amber even though sugar is a carbohydrate?
Why does cooking oil stay amber, and is it a polymer?
What would iodine show on a cracker chewed for a minute, and why?

Part 5 — Analysis Questions

1. Describe your six results in words, comparing each food's color with the plain-water control. Then count how many foods you called starch present, absent, and little, and check that the counts add up to the number of foods you tested.
2. Does your evidence support or fail to support your hypothesis? Write one conclusion sentence that uses supports or fails to support rather than proves, and explain the result from the shape of the molecules in that food.
3. Starch and cellulose are both built from glucose. Using this week's idea that structure determines function, explain why iodine turns blue-black on starch, and say what the test does and does not tell you about a food's total carbohydrate.
4. Chewing a cracker turns it sweet. Name the reaction that happens in your mouth, say which way water moves in it, and predict how a chewed cracker's iodine color would compare with an unchewed one's.
5. Choose one and answer it in 3–4 sentences. (a) Iodine detects only starch: name what your test cannot tell you about the sugar water and what kind of test you would need instead. (b) Name one difference between samples that could have changed your color calls, such as the amount of iodine or the food's own color, and say how you would keep it the same next time.

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 3 Biology Lab & Inquiry table above. I put a drop of iodine solution on six samples on a kitchen counter: plain water as my negative control, a piece of bread, a slice of raw potato, sugar water, cooking oil, and a slice of fruit. Please do six things. First, explain each color result from the structure of the molecules in the food. Second, say which class of macromolecule cooking oil belongs to and whether that class is a polymer. Third, list the four levels of protein structure in order. Fourth, give the percent of starch in each food I tested, with a source. Fifth, as a stretch question for later in the course, say how many cells a body cell makes when it divides for growth. Sixth, as another stretch question, say what phenotype ratio a cross of two Tt parents gives.

Test the response for these likely failures:

• Chatbots often say iodine detects sugar or carbohydrate in general, so they expect sweet foods to turn dark or call an amber result proof that a food has no carbohydrate.
• Chatbots often call cooking oil a polymer, describing a fat as fatty acids repeated in a long chain like starch.
• Chatbots sometimes list the levels of protein structure out of order, putting tertiary before secondary or starting with quaternary.
• Asked for a percent of starch, chatbots often invent a precise percentage for each food and cite a study or a source that was never given.
• Asked the stretch question, chatbots sometimes say a dividing body cell makes four cells or makes cells that differ from each other.
• Asked the stretch question, chatbots sometimes give the phenotype ratio of a Tt by Tt cross as 1:2:1.

Write 3–5 sentences naming one thing the chatbot got right and at least two places it went wrong or overreached, quoting its words and correcting each with evidence from your own table or this week's chapter; mark the stretch answers as ones to check later.

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: "In my iodine lab, the bread and the potato turned blue-black and the sugar water stayed amber, which proves the sugar water has no carbohydrate in it, because iodine detects all sugars. Cooking oil stayed amber because oil is a polymer made of fatty acids repeated in a long chain. My foods were about 40 percent starch for the bread and 15 percent for the potato, as nutrition studies show. A protein folds in this order: tertiary, primary, quaternary, secondary. As a preview of later weeks, a body cell dividing for growth makes four different 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 (an oversimplified mechanism, a mislabeled molecule, an order scrambled, an invented figure, or a preview fact stated wrong), cite the evidence from your table 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 2) 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 samples or the illustrative fallback color calls
• 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 the iodine starch test: three completed tables (the named parts of the test, the six color calls with a predicted class and a structure reason for each, and the reasoning about the surprising results), 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, predictions, and negative control	A falsifiable if… then… because… hypothesis and a prediction for every food appear before the iodine, plain water is named as the negative control, and one condition held the same is named.	A hypothesis appears but is not falsifiable or lacks predictions, or the negative control or the held condition is missing.	No hypothesis, or the parts of the test are not named.
Completed data table with color calls	All six samples are recorded from the student's own test or the fallback calls, each with a color described in words against the control, a starch call, and a predicted class.	The table is filled, but one or two color calls, starch calls, or predicted classes are missing or do not match the recorded color.	No samples are recorded, or the calls are invented rather than observed or taken from the fallback.
Structure-to-function analysis	Questions 1 to 4 are answered accurately: the counts check against the number tested, the conclusion uses supports or fails to support, the blue-black color is tied to starch's coil with amber read as no starch rather than no carbohydrate, and chewing is named as hydrolysis.	The questions are attempted, but one or two answers treat sweetness as starch, call a lipid a polymer, reverse the reactions, or claim the result proves the hypothesis.	The analysis questions are missing or do not address the results.
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 table or the chapter, 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 limit of the iodine test or a specific difference between samples 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 color call in the data table comes from your own samples or the printed fallback calls, never from memory or a chatbot.
• Each color is described in words and compared with the plain-water negative control.
• The hypothesis was written before the first drop of iodine and has the if… then… because… form.
• Each starch call is explained from the shape of the food's molecules, not from its taste.
• No measurement, percentage, 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 table or the chapter.