Domain: Natural Science — Chemistry
Target concept: Catalase and thermally denatured catalase decompose hydrogen peroxide (oxygen)

Video generation prompt: On the lab bench, two transparent test tubes are placed side by side: the one on the left contains catalase, and the one on the right contains heat-denatured catalase; hydrogen peroxide is added to both.

Evaluation guide:
Target Concept: Enzymatic catalysis requires intact protein conformation; thermal denaturation destroys catalytic function without altering chemical identity. Minimum Mechanistic Assumptions: (1) Catalase accelerates H₂O₂ decomposition to O₂ gas and water; (2) O₂ gas manifests as visible, rising, spherical bubbles and stable foam; (3) Denaturation unfolds catalase, obliterating active site geometry; (4) Uncatalyzed H₂O₂ decomposition is negligible on this timescale (<0.1 bubble expected). Phased Storyline: [t=0] Two identical-looking tubes on white bench, labeled LEFT/RIGHT; [t=0.1 s] Simultaneous H₂O₂ addition to both; [t=1–3 s] Left tube erupts with continuous O₂ bubbles → foam nucleation; [t=3–10 s] Left tube sustains dense foam; Right tube remains perfectly still, with no bubbles, no foam, no sound. Visibility Constraints: Frontal, static, well-lit view essential; bubbles must be resolvable (>0.3 mm diameter), foam must be discernible against liquid meniscus; no occlusion; labeling must be legible in final frame.

Manual:
Catalase and Thermally Denatured Catalase Decompose Hydrogen Peroxide (Oxygen) Demonstration Instructions
I. Basic Demonstration Information
Demonstration Title: Catalase Activity vs. Thermal Denaturation in H₂O₂ Decomposition Demonstration
Subject: Natural Science — Chemistry — Enzyme Kinetics & Protein Denaturation
Demonstration Purpose: By side-by-side comparison of native catalase and heat-denatured catalase reacting with hydrogen peroxide, this demonstration visually reveals the essential role of enzyme conformation in biological catalysis; it illustrates that thermal denaturation irreversibly abolishes enzymatic activity; and it enables direct visual recognition of oxygen gas evolution as the key functional output.

II. Demonstration Carrier/Equipment
Core Carrier: Two identical transparent glass test tubes (15×125 mm), labeled “LEFT: CATALASE” and “RIGHT: DENATURED CATALASE” (labels affixed to tube exteriors, unobstructive); fresh bovine liver extract (catalase source, 1 mL, chilled at 4°C); thermally denatured catalase (identical extract boiled for 5 min, then cooled to room temperature, 1 mL); 3% hydrogen peroxide solution (H₂O₂, 2 mL total, pre-measured in separate dropper); white tile or light-colored lab bench background (to enhance bubble contrast).
Auxiliary Equipment: Dropper with fine tip (for controlled H₂O₂ addition); timer (optional, for consistency); safety goggles and gloves (mandatory).

III. Demonstration Content Description
Layout: Place both test tubes upright and parallel on a clean, dry, white-tiled lab bench. Left tube contains 1 mL native catalase solution (amber-tinted, slightly cloudy, homogeneous liquid). Right tube contains 1 mL heat-denatured catalase (same initial appearance: amber-tinted, slightly cloudy, homogeneous — indistinguishable by sight before reaction). Both tubes are at room temperature (20–25°C) and motionless prior to addition.
State Control: Ensure no prior agitation or contamination; solutions must be freshly prepared (denatured sample verified by prior boiling and cooling). No stirring or shaking after H₂O₂ addition — rely on spontaneous reaction.
Comparison Baseline: Identical tube geometry, volume, lighting, and viewing angle (frontal, eye-level, ~30 cm distance); H₂O₂ added simultaneously (within <0.5 s) to both tubes using the same dropper — 1 mL per tube.

IV. Observation of Core Phenomena
Left Tube (Native Catalase + H₂O₂): Within 1–3 seconds of addition, vigorous effervescence begins — continuous stream of small, colorless, spherical bubbles rises rapidly through the liquid column. Bubbles coalesce at the surface, forming persistent foam layer (2–5 mm height) that lasts ≥8 seconds. Liquid remains amber and translucent; no color change or precipitation. Gas evolution is loud enough to hear faint hissing/bubbling sound.
Right Tube (Denatured Catalase + H₂O₂): No visible bubbling within first 5 seconds. At most, 1–2 isolated, slow-rising, large, irregular bubbles appear between 5–10 s (spontaneous decomposition only). No foam formation. Liquid remains amber and unchanged in clarity or color. No audible gas evolution sound.
Characteristic Stability: The contrast is immediate, sustained, and unambiguous — left tube shows *active, rapid, voluminous O₂ evolution*; right tube shows *no functional catalytic activity*. The difference is stable for ≥10 s — sufficient for full observation and verification.
Auxiliary Comparison: Both tubes start with identical visual properties (color, turbidity, meniscus shape); divergence occurs *only after* H₂O₂ addition and is attributable *exclusively* to structural integrity of catalase — confirming protein conformation as the causal determinant of function.

V. Summary of Key Knowledge Points and Principles
Core Concept Definition: Catalase is a globular enzyme that catalyzes 2H₂O₂ → 2H₂O + O₂. Its activity depends entirely on its precise 3D tertiary/quaternary structure. Thermal denaturation disrupts hydrogen bonds and hydrophobic interactions, unfolding the protein and destroying the active site — rendering it catalytically inert, though chemical composition remains unchanged.
Scientific Significance:
- Enzyme Specificity & Structure–Function Relationship: Demonstrates that biological activity is not inherent to amino acid sequence alone, but to folded conformation.
- Irreversibility of Thermal Denaturation: Boiling permanently inactivates catalase — no spontaneous refolding occurs under these conditions.
- Visual Proxy for Reaction Rate: Oxygen bubble volume, frequency, and foam persistence serve as direct, real-time macroscopic proxies for enzymatic turnover rate.
Further Knowledge: Non-enzymatic H₂O₂ decomposition is extremely slow at room temperature (half-life ~10⁴ years); observed trace bubbles in the right tube reflect only negligible uncatalyzed breakdown — confirming the dominance of enzymatic catalysis in the left tube.

VI. Demonstration Precautions
- Safety: Wear goggles — H₂O₂ may spatter during vigorous reaction. Do not seal tubes — pressure buildup risk.
- Timing: Add H₂O₂ *simultaneously* — delay >0.5 s between tubes invalidates comparative validity.
- Authenticity: Denatured sample must be *boiled*, not just heated — confirm by prior validation (e.g., no activity in pilot test). Native catalase must be cold-stored and used immediately to prevent autolysis.
- Visibility: Use white background and frontal lighting — shadows or backlighting obscure bubble detection. Avoid camera motion or zoom during reaction phase.
- Duration: Observation window is 0–10 s post-addition — all diagnostic phenomena occur within this timeframe.

Prompt Grounding rubric:
level_1: The two test tubes are missing, not shown side by side, or unlabeled; the left/right positions of the native-catalase and heat-denatured-catalase tubes are swapped from what the prompt describes; the two tubes look different from each other before H₂O₂ is added (e.g., one is empty, discolored, or has visible clumps); H₂O₂ is poured into only one tube; or the addition itself is never shown on screen.
level_2: Both tubes appear together, but their labels are missing, wrong, or too small or blurry to read; the two liquids look different from each other before addition (one clear and one hazy, or different tints); H₂O₂ is added to the two tubes more than about a second apart; the tubes are not clear glass or plastic; or the tabletop background is dark or cluttered rather than plain and light.
level_3: Tubes are correctly placed together, clearly labeled, and made of clear material; the two liquids look like the same pale amber, slightly hazy solution before addition; H₂O₂ is added to both, but with a noticeable half-second-to-one-second gap between the two additions; the background is acceptably plain but somewhat shadowed; a hand briefly blocks the view of one tube during the addition.
level_4: The left tube is clearly labeled 'CATALASE' and the right tube 'DENATURED CATALASE'; both tubes are upright, parallel, and identical in size on a plain light background; the two liquids look the same in color and haziness before addition; H₂O₂ is added to both tubes close enough together that no separate delay is noticeable; nothing blocks either tube; lighting is even and from the front.
level_5: Tubes are evenly spaced, upright, and fully visible with legible left/right labels matching the prompt; the native and heat-denatured solutions look identical to the eye in color, haziness, and liquid-surface shape before addition; H₂O₂ is poured into both tubes at essentially the same moment, with no noticeable lag between the two; the background stays plain and glare-free; the camera holds a steady, centered framing that keeps both full tubes in view throughout.

Scientific and Causal Correctness rubric:
level_1: Neither tube produces gas bubbles, or both tubes bubble vigorously, or foam appears in the denatured-catalase tube, or either liquid changes color or forms a precipitate, or bubbling begins before the H₂O₂ is even added; any of these contradicts how an active enzyme differs from a heat-denatured one.
level_2: The native-catalase tube bubbles, but only weakly or after a long delay (more than about five seconds); the denatured-catalase tube produces three or more bubbles or brief foam despite having no active enzyme; bubbling in the native tube stalls for gaps of more than a second instead of continuing steadily.
level_3: The native-catalase tube starts bubbling within about 3 seconds, but the bubbles are large, irregular, or sparse rather than a steady fine stream; any foam that forms collapses within about 3 seconds; the denatured-catalase tube shows only one or two bubbles appearing between roughly 5 and 10 seconds, with no foam; neither liquid changes color.
level_4: The native-catalase tube produces a steady stream of small, rising bubbles beginning within about 1-2 seconds of H₂O₂ contact, building a foam layer roughly 2-4 mm high that lasts at least 6 seconds; the denatured-catalase tube stays essentially still for the first 5 seconds, with at most one or two slow, isolated bubbles appearing between about 6 and 10 seconds; no foam or color change appears in the denatured tube.
level_5: The native-catalase tube erupts within about 1 second into a dense, continuous stream of small, evenly rising bubbles that builds a fine-textured foam roughly 3-5 mm high within 2 seconds and sustains it for the full 10-second clip; the denatured-catalase tube remains completely undisturbed (no bubbles, no foam, no change to its liquid surface) from start to end, making the contrast between the active and the heat-inactivated enzyme unmistakable and clearly tied to the moment H₂O₂ touches each tube.

Spatiotemporal Consistency rubric:
level_1: Frames jump, freeze, or play in reverse; bubbles appear or vanish without rising through the liquid; either tube shifts position on its own; the liquid level in a tube changes with no visible cause; the lighting flickers or changes abruptly partway through.
level_2: Bubble rise speed is uneven or jerky in a way that looks unnatural; the frame rate seems inconsistent; one tube visibly wobbles or tilts without cause; foam appears fully formed in a single frame instead of building up from bubbles; the background lighting shifts in color partway through.
level_3: Bubbles mostly rise at a believable, steady speed and foam builds up gradually; both tubes stay in place; but the camera view shakes or drifts slightly in a clearly noticeable way, or bubble sizes vary inconsistently from moment to moment; lighting stays roughly steady but is a little uneven between the two tubes.
level_4: Bubbles rise smoothly at a consistent, believable speed and foam thickens gradually before leveling off; the camera holds a steady, unmoving frame; lighting stays even and comes from the front throughout; the curved liquid surface in both tubes looks the same before and after H₂O₂ is added.
level_5: Bubbles rise straight upward at a steady, believable pace with no sideways drifting, and foam thickness and bubble density build up smoothly and continuously with no sudden jumps; the camera view stays perfectly steady with no visible shake; the camera framing, lighting angle, and overall shadow pattern do not shift for the whole clip; if a hand is shown adding the H₂O₂, it moves naturally and leaves the frame cleanly right after.