Week 5 — Lab / Scientific Inquiry · "Catalase & the Temperature of Life"

Course: Introduction to Biology — General Biology I (BIOL 101) · Silver Oak University (fictional sample) · Prof. Castellano
Objective: Objective 4 — observe an enzyme at work; test how temperature changes its rate; identify variables; collect and interpret data · SLO A (scientific reasoning) · SLO B (an enzyme's structure → function)
Worth 50 points · Labs group = 15% of the grade · Lab 5
Format: a hands-on at-home enzyme experiment (raw potato or liver + hydrogen peroxide) — you'll run the enzyme at four temperatures, build a data table, graph the rate, 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 that enzymes speed reactions by lowering activation energy, that each enzyme has an optimum temperature, and that too much heat denatures the enzyme — destroying its active site so the rate crashes to zero. Now you'll watch that happen with a real enzyme.

The phenomenon: living cells make a toxic byproduct, hydrogen peroxide (H₂O₂), and an enzyme called catalase rapidly breaks it down into harmless water and oxygen gas. Raw potato and raw liver are loaded with catalase. Drop a piece into hydrogen peroxide and the oxygen bubbles up as foam — the more foam (and the faster it rises), the faster the enzyme is working. By running the same reaction at four temperatures, you'll map catalase's temperature curve and see denaturation with your own eyes.

Background (optional, ~6 min): Amoeba Sisters — "Enzymes (Updated)" (covers active site, substrate, and how temperature affects enzymes): 🔗 https://www.youtube.com/watch?v=qgVFkRn8f10

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Part 2 — Your Scientific Question & Hypothesis

The question: How does temperature change how fast catalase breaks down hydrogen peroxide — and what happens when the enzyme is boiled?

Before you start, write your hypothesis (an "if… then… because…" statement is perfect):

If I increase the temperature of the potato/liver toward body temperature, then the amount of oxygen foam will __, but if I boil the enzyme first, then _, because ___.

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):
- A raw potato (or a small piece of raw liver) · 3% hydrogen peroxide (the brown drugstore bottle) · 4 identical clear cups or glasses · a knife and a way to make equal-size pieces (or a measuring spoon of grated potato) · a ruler · a clock/phone timer · access to ice water, room-temperature water, warm (~body-temperature) water, and boiling water (adult care with hot water).

Set up four temperature conditions for the enzyme:
1. Cold (~5 °C): chill several potato pieces in ice water for 10 minutes.
2. Room (~22 °C): leave several pieces at room temperature.
3. Body (~37 °C): warm several pieces in warm tap water (about bath-warm, not hot) for 10 minutes.
4. Boiled (~100 °C, denatured): boil several pieces in water for 5 minutes, then let them cool back to room temperature before testing. (This destroys the enzyme but not the potato — that's the point.)

Procedure (run each condition the same way):
1. Put the same amount of hydrogen peroxide (e.g., 50 mL) into each of the 4 cups.
2. Add one equal-size piece of potato/liver from a condition to its cup and immediately start the timer.
3. After exactly 60 seconds, measure the height of the foam (in cm) above the liquid with your ruler. Record it.
4. Repeat so you have 3 trials per condition (use fresh peroxide and a fresh equal-size piece each trial).
5. Hold these the same every trial (your controlled variables): the same peroxide concentration and volume, the same size/amount of potato, the same timing (60 s), the same cup, the same person measuring.

No household items handy? You can run an equivalent virtual enzyme experiment in a free simulation, or simply use the model data table in Part 8 to practice the analysis — but the at-home version takes about 20 minutes and is far more satisfying to watch.

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Part 4 — Data Table (fill this in)

Record the foam height (cm) after 60 seconds for each trial, then average.

Condition (temperature)	Trial 1	Trial 2	Trial 3	Average (mean)
Cold (~5 °C)	______	______	______	______
Room (~22 °C)	______	______	______	______
Body (~37 °C)	______	______	______	______
Boiled (~100 °C)	______	______	______	______

Mean = (Trial 1 + Trial 2 + Trial 3) ÷ 3. Show your arithmetic.

Then make a quick graph: temperature on the x-axis, average foam height (rate) on the y-axis. Connect the points. Describe the shape in one sentence.

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Part 5 — Identify Your Experiment's Parts

Answer in a sentence each:
1. Independent variable (what you changed): __
2. Dependent variable (what you measured): _
3. Two controlled variables (kept the same):
4. Control / comparison (your baseline for "the enzyme working normally"): ___

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Part 6 — Analysis Questions

1. At which temperature was the reaction fastest (most foam)? At which was it slowest or zero? Does your graph rise to a peak and then drop?
2. Explain the result using activation energy and the enzyme's optimum. Why does warming toward ~37 °C speed catalase up?
3. Why was the boiled sample's rate so low (ideally near zero)? Use the word denature, and explain why this is different from the cold sample just being slow.
4. Why did you run three trials per condition and take an average? What does that protect you from?
5. Connect it: a fever raises body temperature above ~37 °C. Based on your curve, what would happen to your enzymes during a moderate fever, and why is a very high fever dangerous? (Tie it to denaturation.)

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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 results. At which temperature is catalase fastest, what's the average foam height for each condition, and what does the boiled result mean? Also tell me the independent and dependent variables."
2. Check everything it says against your own work:
   - Did it calculate the averages correctly? (Re-add your three trials and divide by 3 yourself.)
   - Did it correctly say the rate is highest near body temperature and lowest when boiled — or did it claim "hotter is always faster" and call the boiled tube the fastest? (Chatbots do this constantly.)
   - Did it get the science right — that boiling denatures the enzyme (permanent), versus cold just slowing it (reversible)? Or did it say the enzyme was "used up" or "ran out"?
   - Did it correctly label the independent variable as temperature and the dependent variable as foam height/rate — or did it swap them?
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 — that's the skill.)

The habit all term: the tool drafts, you judge. A chatbot will confidently say "hotter is always faster" or mis-add a column — 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 with all four averages, your graph (a photo or sketch is fine), your Part 5 variable labels, your Part 6 answers, and your Part 7 AI-critique paragraph. Due Sunday, Oct 4, 11:59 p.m. (50 points).

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

Students collect their own numbers, so exact foam heights vary (potato vs. liver, peroxide freshness, piece size). The model dataset below is for grading the analysis and the trend; all numbers are pre-computed and independently verified. The gradable facts are the trend (rate rises to a ~37 °C optimum, then crashes) and that the boiled/denatured sample ≈ 0 — not any one student's exact centimeter reading.

Model data table (illustrative, clean values — foam height in cm at 60 s):

Condition	Trial 1	Trial 2	Trial 3	Mean	Relative rate
Cold (~5 °C)	1	2	3	2	2
Room (~22 °C)	4	5	6	5	5
Body (~37 °C)	9	10	11	10 (peak)	10
Boiled (~100 °C)	0	0	0	0	0

• Cold mean = (1 + 2 + 3) ÷ 3 = 6 ÷ 3 = 2 cm. ✓
• Room mean = (4 + 5 + 6) ÷ 3 = 15 ÷ 3 = 5 cm. ✓
• Body (37 °C) mean = (9 + 10 + 11) ÷ 3 = 30 ÷ 3 = 10 cm — the peak. ✓
• Boiled mean = (0 + 0 + 0) ÷ 3 = 0 cm — denatured. ✓
• Trend: rate rises from cold → room → body (2 → 5 → 10), peaking at the ~37 °C optimum, then crashes to 0 when boiled. The 37 °C rate is 5× the cold rate and 2× the room rate (10/2 and 10/5) — illustrative, clean ratios.

Expected answers:
- Part 5: (1) IV = temperature of the enzyme (5/22/37/100 °C); (2) DV = foam height / reaction rate at 60 s; (3) two of: same peroxide concentration & volume, same potato size/amount, same 60 s timing, same cup, same measurer; (4) baseline = the body-temperature (~37 °C) sample (the enzyme working at its optimum), with room temperature also acceptable as the "ordinary" comparison.
- Part 6: (1) Fastest at ~37 °C; slowest/zero when boiled; the graph rises to a peak then drops. (2) Warming gives molecules more energy → more frequent, more successful collisions in the active site, so the rate rises toward the optimum; the enzyme lowers the activation energy so each collision is more likely to react. (3) Boiling denatures catalase — the protein unfolds and the active site is destroyed, so it can't bind peroxide; rate ≈ 0. This is permanent, unlike the cold sample, which is merely slowed and would speed up if warmed. (4) Three trials + averaging reduces random error (an odd piece, a mis-timed reading) for a more reliable result. (5) A moderate fever pushes enzymes slightly past their optimum, so many reactions run a bit wrong at once (you feel "off all over"); a very high fever (≈41–42 °C) risks denaturing enzymes — which is why it's a medical emergency, not just discomfort.
- Part 7 (AI-critique): full credit for a specific catch — most commonly the AI claiming "hotter is always faster" (calling the boiled tube fastest), mis-adding an average, swapping IV and DV, or saying the enzyme was "used up" rather than denatured. Full credit also if the student verified each AI claim against their own data and reasoning.

Grading rubric — 50 points

Criterion	Full	Partial	None
Hypothesis — a clear, testable "if…then…because…" prediction covering warming AND boiling (8)	8	4–6	0–2
Data table + graph — three trials per condition, four means computed correctly, a graph showing rise-then-crash (15)	15	8–12	0–6
Variables (Part 5) — IV (temperature), DV (foam/rate), two constants, and a sensible baseline all correct (12)	12	6–10	0–4
Analysis (Part 6) — fastest at optimum + boiled ≈ 0 explained with denature (vs. cold = just slow) + why replicate/average (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): every number in the model dataset is pre-computed and independently re-verified by a Python check — means 2, 5, 10, 0; the trend rises to a ~37 °C optimum then crashes to 0 when boiled; ratios (37 °C is 5× cold, 2× room) re-derived clean — quantitative gate: PASS. The science is correct (warming → faster up to the optimum; boiling denatures → rate 0, permanent; cold merely slows, reversible); variables map correctly (IV = temperature, DV = foam height/rate). No student-collected number is asserted as "the" answer — the key grades the trend and the denaturation fact, not a specific foam height.