Domain: Natural Science — Biochemistry & Molecular Biology
Target concept: Lactate dehydrogenase catalyzed reaction (a key enzymatic reaction in glycolysis and lactate metabolism)

Video generation prompt: Add pyruvate and NADH solution to a test tube containing lactate dehydrogenase, and gently mix at room temperature.

Evaluation guide:
(i) Target concept: Enzyme-catalyzed redox reaction in which lactate dehydrogenase converts a concentrated NADH solution to NAD⁺, with reaction progress reflected in a subtle fading of NADH's characteristic pale-yellow tint.
Minimum mechanism: Pyruvate and a sufficiently concentrated NADH solution must coexist with active LDH in aqueous phase at neutral pH and room temperature to drive the forward reaction; as NADH (the pale-yellow, ~340 nm-absorbing species) is consumed and converted into colorless NAD⁺, the solution's initial pale-yellow tint should visibly lighten rather than deepen; note that this tint is inherently subtle and only becomes perceptible to the unaided eye at NADH concentrations well above those used in a standard spectrophotometric assay.
(ii)Storyline: [Frame 0–2] Static shot: test tube centered, containing LDH (visible as fine powder or clear solution). [Frame 3–4] Pyruvate solution enters frame from top and dispenses into tube. [Frame 5–6] Concentrated NADH solution enters frame from top and dispenses into same tube, giving the mixture a faint pale-yellow cast. [Frame 7–10] Hand/tube rotates/swirls continuously; solution remains fully contained; the pale-yellow tint gradually fades toward a paler, near-colorless appearance by the final frame. Perspective: fixed frontal view, shallow depth of field emphasizing tube contents; no occlusion of liquid column during mixing; all events occur within a single continuous take.

Manual:
Experimental Procedure
1. Place a clean test tube containing lactate dehydrogenase (as solid powder or clear solution).
2. Add pyruvate solution to the tube.
3. Add a concentrated NADH solution to the same tube.
4. Gently mix by swirling or inversion at room temperature.
Observation of Experimental Phenomena
The starting solution carries a faint pale-yellow tint contributed by NADH; as the LDH-catalyzed reaction proceeds and NADH is oxidized to NAD⁺, this pale-yellow tint gradually fades toward a paler, near-colorless appearance (the tint is subtle and requires a concentrated NADH stock to be visible to the unaided eye); no precipitate, bubble, or turbidity appears.
Summary of Experimental Principles
Lactate dehydrogenase catalyzes the reversible conversion of pyruvate + NADH + H⁺ ⇌ lactate + NAD⁺. NADH (not NAD⁺) absorbs at ~340 nm and, at sufficiently high concentration, imparts a faint pale-yellow tint to the solution; NAD⁺ itself is colorless. As NADH is oxidized to NAD⁺ during the forward reaction, this pale-yellow tint fades rather than intensifies.

Prompt Grounding rubric:
level_1: The test tube containing lactate dehydrogenase is not shown, or neither the pyruvate solution nor the NADH solution is added into it; no addition action and no mixing action of any kind appear on screen.
level_2: The test tube is visible, but at least two of the three required components (pyruvate solution, NADH solution, lactate dehydrogenase already in the tube) are missing, unidentifiable, or replaced by an unrelated substance; only one reagent is shown being added, or no mixing motion follows the addition(s).
level_3: The test tube already holding lactate dehydrogenase (as a powder or a clear pre-existing solution) is shown; pyruvate solution and NADH solution are each added into that same tube, one after the other or together; a gentle swirling or inversion mixing motion follows both additions.
level_4: Everything required for score 3 is present, and in addition: the pyruvate and NADH additions are both directed into the tube that already contains the lactate dehydrogenase (neither reagent is pre-mixed in a separate vessel first); mixing begins only after both reagents have been added; no extraneous action interferes with reading the setup (e.g., no dropper touching the tube rim, no unlabeled container obscuring which reagent is which).
level_5: Everything required for score 4 is present, and in addition: the pyruvate and NADH solutions are delivered from two visually distinct containers or droppers (different color, shape, or label) so the two additions are individually trackable; the lactate dehydrogenase is unambiguously shown inside the tube before either liquid is added; the swirling/inversion mixing is one continuous, uninterrupted motion confined to the tube, with no pause, reversal, or restart.

Scientific and Causal Correctness rubric:
level_1: No color change occurs anywhere in the sequence; the solution's appearance is static throughout, showing no causal link between the pyruvate/NADH addition-and-mixing and any visual change.
level_2: A color change occurs, but it contradicts the LDH reaction (e.g., the solution turns blue, purple, green, or an opaque white); or the tint changes before pyruvate, NADH, and enzyme have all combined; or the solution darkens/turns more yellow instead of fading; or turbidity/precipitate appears without any chemical basis for it.
level_3: After the pyruvate and NADH are both mixed with the lactate dehydrogenase, the solution's initial pale-yellow tint (carried by the NADH) visibly fades toward a paler, less-yellow appearance; the solution stays clear with no precipitate or cloudiness; the fading proceeds continuously rather than as an instant jump or a flicker.
level_4: Everything required for score 3 is present, and in addition: the fading begins only once mixing starts, not merely upon addition of the reagents; the end state is a paler/near-colorless solution consistent with NADH being converted into colorless NAD⁺; no contradictory visual cues appear, such as bubbling, streaky unmixed patches, or a pocket of liquid that stays more yellow than the rest.
level_5: Everything required for score 4 is present, and in addition: the fade is smooth and one-directional (the tint only ever grows paler, never darkens or flickers back) and becomes fully uniform across the whole solution by the last frame; the final hue matches a dilute, near-colorless NAD⁺-containing solution under ordinary room lighting, with no incidental green, pink, blue, or brown cast.

Spatiotemporal Consistency rubric:
level_1: The test tube vanishes partway through the shot or is replaced by a differently shaped/sized tube; the pyruvate or NADH solution appears in the tube with no visible addition motion; the room lighting jumps abruptly between frames; the swirling/mixing motion skips or jump-cuts; the tube rotates by more than about 30 degrees or shifts position by more than about a third of its width between frames.
level_2: The tube shifts position or tilts noticeably, by less than about a third of its width, but without a clean, continuous motion (a small jump rather than a smooth move); the swirling/mixing motion freezes momentarily one or more times before resuming; the lighting on the tube shifts unevenly (e.g., a highlight jumps across the glass) without any corresponding change in the room; a hand or dropper shadow appears and disappears without a visible cause.
level_3: The test tube stays in the same place and orientation throughout, aside from the intended swirling/inversion motion; the pyruvate solution and NADH solution each enter the frame only via a visible pouring/dropper motion, never appearing mid-tube without an entry; the mixing motion is one continuous action confined to inside the tube; the lighting on the tube and any cast shadow change smoothly and only as much as the swirling motion itself would cause.
level_4: Everything required for score 3 is present, and in addition: the hand, dropper, or tube holder keeps a consistent spatial relationship to the tube throughout delivery and mixing (e.g., a dropper tip stays aligned with the tube opening rather than drifting away from it); no part of the tube or liquid warps, stretches, or changes proportions between frames; the swirling motion runs at a constant, natural pace with no sped-up or slowed-down segment.
level_5: Everything required for score 4 is present, and in addition: the tube holds a rock-steady position with no small drifts or wobbles in its outline from one frame to the next; the hand/dropper and the tube maintain consistent relative depth and scale as they move (no floating or size mismatch); no liquid trail lingers in the air after the dropper is withdrawn, and no ghost outline of the tube or hand persists after it moves away; the swirling and mixing look like one smooth, uninterrupted take rather than a stitched-together sequence.