Week 3 — Lab / Scientific Inquiry · "Testing for Macromolecules in Food"

Course: Introduction to Biology — General Biology I (BIOL 101) · Silver Oak University (fictional sample) · Prof. Castellano
Objective: Objective 2 — detect biological macromolecules in food; connect a chemical test to a molecule's structure; collect and interpret data · SLO A (scientific reasoning) · SLO B (structure → function)
Worth 50 points · Labs group = 15% of the grade · Lab 3
Format: a hands-on at-home chemical test (one common household item) — you'll predict, test, build a data table, and then catch the AI's mistakes when it interprets your results.

This is the course's signature weekly component. Every instructional week has one lab. This week's is a simple at-home protocol; later weeks use free virtual simulations (a virtual microscope, PhET, HHMI BioInteractive, LabXchange, Learn.Genetics). All lab resources are links to external sites — nothing to buy or download.

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Part 1 — The Big Picture

This week you learned the four macromolecule families and the theme that structure determines function. Scientists detect these molecules using chemical indicator tests — and each test works because of the molecule's structure. The classic one you can run at home is the iodine test for starch: iodine solution is normally amber/brown, but when it slips into the coiled, helical structure of starch, it turns a dramatic blue-black. No starch → it stays amber. The color change is literally structure → function: the test "sees" starch's particular shape.

Two related tests (which you'll reason about, even if you can't run them at home) round out the picture:
- Benedict's test detects simple/reducing sugars (like glucose): blue → green → orange/brick-red when heated, more sugar = redder.
- Biuret test detects proteins (peptide bonds): blue → violet/purple when protein is present.

Background (optional, ~7 min): Amoeba Sisters — "Biomolecules" (a quick tour of carbs, lipids, proteins, and nucleic acids): 🔗 https://www.youtube.com/watch?v=YO244P1e9QM

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Part 2 — Your Scientific Question & Hypothesis

The question: Which everyday foods contain starch — and which do not — as revealed by the iodine test?

Before you start, write your hypothesis (an "if… then…" statement is perfect). Pick a food you're unsure about (say, a cracker or an apple):

If I add iodine to __ (your test food), then it will turn _ (blue-black / stay amber), because I think it ___ (does / does not) contain starch.

Write it down now — you'll compare it to your results at the end. (A "wrong" prediction is completely fine; science is about testing, not guessing right.)

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Part 3 — Materials & Procedure

You need (all common household items):
- Tincture of iodine (the small brown bottle from a pharmacy first-aid aisle) or Betadine/povidone-iodine — for external use; do not eat the tested samples · an eye-dropper (usually built into the iodine cap) · a white plate or several small white dishes/paper towels (white background shows the color best) · small samples of 5 foods, suggested: a piece of bread or cracker, a slice of potato, sugar water (a teaspoon of table sugar stirred into a little water), a piece of apple or other fruit, and cooking oil (or a piece of cheese). · paper towels and gloves if you have them.

Safety: iodine stains skin, clothes, and counters and is not for eating — work over a paper towel, don't taste any sample after adding iodine, and keep it away from kids and pets. A small spill wipes/washes off skin in a day.

Procedure:
1. Place a small amount of each food on the white plate, well separated, and label each spot (bread, potato, sugar water, apple, oil).
2. Add 2–3 drops of iodine directly onto each food sample.
3. Wait about 30–60 seconds and watch the color.
4. Record the color for each: blue-black/dark = starch present; stays amber/brown = no starch.
5. Hold these the same for every sample (your controlled variables): the same iodine bottle, the same number of drops, the same wait time, the same lighting/white background.

No iodine handy? You can still complete the lab using the model data table in Part 8 to practice the analysis and the AI-critique — but the at-home version takes ten minutes and the blue-black color is genuinely satisfying to see.

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Part 4 — Data Table (fill this in)

Food sample	Your prediction (starch? Y/N)	Color after iodine	Starch present? (Yes / No)
Bread or cracker	______	______	______
Potato	______	______	______
Sugar water	______	______	______
Apple (or fruit)	______	______	______
Cooking oil (or cheese)	______	______	______

Record the actual color you see (e.g., "blue-black," "stayed amber"). The iodine test is qualitative — there is no arithmetic, just a clear color call.

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Part 5 — Identify Your Experiment's Parts

Answer in a sentence each:
1. Independent variable (what you changed from sample to sample): __
2. Dependent variable (what you observed/measured): _
3. Two controlled variables (kept the same):
4. A negative control (a sample you expect to test NEGATIVE for starch, giving you a baseline "amber" to compare against): ___

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Part 6 — Analysis Questions

1. Which foods tested positive for starch (turned blue-black), and which stayed amber? Did any result surprise you versus your prediction?
2. Connect it to structure → function. The iodine test works because iodine fits into starch's coiled, helical structure. Why is it useful that the same drop of iodine gives a clear yes/no for one specific molecule? (Hint: a test that "sees" a molecule's shape is reading its structure.)
3. Sugar water has sugar but usually tests NEGATIVE for starch with iodine. Explain why, using the difference between a monosaccharide/disaccharide and a polysaccharide. Which other test (named in Part 1) would you use to detect that sugar?
4. Bread is mostly starch, a polymer of glucose. If you chewed a cracker for a full minute, salivary amylase (an enzyme) would begin breaking the starch down. Which reaction is that — dehydration synthesis or hydrolysis — and what smaller molecule would start to appear?
5. Name one source of error in your test (a confusing color, a dark-colored food masking the result, too little iodine) and how you'd improve the procedure next time.

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Part 7 — AI-Critique Moment (required — this is the BYOAI step)

Now bring in your approved chatbot (Gemini, Claude, or ChatGPT) and be the scientist who checks its work.

1. Paste your data table into the chatbot and ask it: "Interpret my iodine test results. Which foods contain starch, and what does the blue-black color mean? Also: is starch a polymer, and what is its monomer? And which reaction breaks starch down during digestion?"
2. Check everything it says against your own work and this week's class:
   - Did it correctly read blue-black = starch present and amber = no starch (not reversed)?
   - Did it correctly call starch a polymer of glucose (monosaccharide) — or did it slip and call it a lipid, or list the wrong monomer?
   - Did it correctly name hydrolysis as the reaction that breaks starch down in digestion — or did it say "dehydration synthesis" (the building reaction) by mistake?
   - Watch for a confident over-claim, e.g., that iodine also detects sugars or proteins (it doesn't — that's Benedict's and Biuret).
3. Write 2–3 sentences reporting what the AI got right and at least one thing you had to correct or watch carefully. (If it happened to get everything right, say how you verified each claim against your data and the week's definitions — that's the skill.)

The habit all term: the tool drafts, you judge. A chatbot will confidently reverse a color key, mislabel a molecule's class, or swap the build/break reactions — catching it is the point.

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Part 8 — What to Submit

Submit a single document (or text entry) with: your hypothesis, your completed data table, your Part 5 variable labels, your Part 6 answers, and your Part 7 AI-critique paragraph. Due Sunday, Sep 20, 11:59 p.m. (50 points).

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Instructor answer key & model data — REMOVE BEFORE PUBLISHING TO STUDENTS

Students collect their own observations, so exact wording varies, but the iodine result is deterministic by food type — the model table below is the vetted key. This is a qualitative lab: there is no arithmetic (quantitative gate: not applicable). All results were verified against the standard behavior of the iodine–starch test.

Model data table (vetted key):

Food sample	Color after iodine	Starch present?
Bread or cracker	Blue-black	Yes (starch-rich)
Potato	Blue-black (often intense)	Yes (starch-rich)
Sugar water	Stays amber	No (sugar is not starch)
Apple (or fruit)	Stays amber / very slight	No / minimal (mostly simple sugars + fiber, little free starch)
Cooking oil (or cheese)	Stays amber	No (oil = lipid; cheese = protein/fat)

Expected answers:
- Part 5: (1) IV = the type of food tested. (2) DV = the color the iodine turns (i.e., starch present or not). (3) two of: same iodine, same number of drops, same wait time, same lighting/background. (4) negative control = a sample expected to test negative — e.g., sugar water, oil, or plain water (gives the baseline amber to compare against). (Accept any food the student correctly expects to be starch-free.)
- Part 6: (1) Bread and potato test positive (blue-black); sugar water, apple, oil stay amber. (2) The test is specific to starch's helical structure, so one reagent gives a clean yes/no for one molecule — a structure-reading test. (3) Sugar water contains a monosaccharide/disaccharide (table sugar = sucrose), not a polysaccharide; iodine only reacts with the long coiled chains of a polysaccharide like starch — so sugar water tests negative. Use Benedict's test to detect the sugar. (4) Hydrolysis — amylase adds water to break starch's bonds; the smaller molecule that appears is glucose (maltose then glucose). (Many students notice a cracker tastes sweeter the longer they chew — that's hydrolysis releasing sugar.) (5) Reasonable errors: dark-colored foods masking the color, too little iodine, a wet sample diluting it — fix by using a white background, enough drops, and a fresh sample.
- Part 7 (AI-critique): full credit for a specific catch — most commonly the AI reversing the color key (calling amber "starch present"), mislabeling starch's class/monomer, naming "dehydration synthesis" instead of hydrolysis for digestion, or over-claiming that iodine detects sugars/proteins. Full credit also if the student verified each AI claim against their own data and the week's definitions.

Grading rubric — 50 points

Criterion	Full	Partial	None
Hypothesis — a clear, testable "if…then…" prediction with a reason (8)	8	4–6	0–2
Data table — all five foods tested with a recorded color and a Yes/No starch call (15)	15	8–12	0–6
Variables (Part 5) — IV, DV, two constants, and a valid negative control all correct (12)	12	6–10	0–4
Analysis (Part 6) — correct starch calls + structure→function reasoning + the monosaccharide-vs-polysaccharide and hydrolysis answers (10)	10	5–8	0–4
AI-critique (Part 7) — names a specific thing checked/corrected in the AI's interpretation (5)	5	3	0–2

Quality gate (self-checked): the iodine–starch key is correct and deterministic (blue-black = starch present in bread and potato; amber = no starch in sugar water, oil, fruit); the science maps correctly (starch = polysaccharide/polymer of glucose; sugar water = monosaccharide/disaccharide, tests negative; digestion of starch = hydrolysis → glucose; structure → function = the color reads starch's helical shape). This is a conceptual, qualitative lab — there is no arithmetic to mis-key (quantitative gate: not applicable). No student-collected observation is asserted as "the" answer beyond the deterministic iodine result; the key grades the reasoning and the correct color calls.