Domain: Natural Science — Biochemistry & Molecular Biology
Target concept: Iodine solution reacts with starch in food samples (potato vs. sucrose)

Video generation prompt: On the lab bench, a raw potato is on the left and a piece of white sugar is on the right; iodine solution is added to each separately.

Evaluation guide:
(i) Target concept: Starch-iodine reaction specificity for polysaccharide detection.
Minimum mechanism: Iodine must be molecular I₂ dissolved in KI solution (amber-brown), potato must contain intact amylose-rich tissue, sugar must be pure sucrose (no starch contamination), and contact must enable aqueous-phase complex formation.
(ii)Storyline: [Frame 0–2] Static wide shot: lab bench with raw potato (left) and white sugar (right) fully visible, unmoving, under even illumination. [Frame 3–4] Dropper enters frame from top, holding amber-brown iodine; no occlusion of materials. [Frame 5–6] Iodine stream contacts potato surface → immediate localized dark blue-black appearance. [Frame 7–8] Iodine stream contacts sugar surface → zero color/texture change. [Frame 9–10] Final static hold: both materials retain their respective post-contact states, left-right spatial integrity preserved, fixed viewpoint, no motion after contact.

Manual:
Experimental Procedure
1. Place raw potato (brown-skinned, irregular solid) on left side of lab bench.
2. Place white sugar (bright white, granular crystals) on right side of lab bench.
3. Using a dropper, add iodine solution (amber-brown liquid) separately to surface of potato and surface of sugar.
Observation of Experimental Phenomena
- Raw potato turns dark blue-black where iodine contacts it.
- White sugar remains bright white with no color change.
Summary of Experimental Principles
Iodine forms a blue-black complex with amylose starch in potato cells; sucrose (white sugar) contains no starch and thus shows no reaction with iodine.

Prompt Grounding rubric:
level_1: No lab bench visible; neither raw potato nor white sugar present; no iodine solution container or dispensing action; scene is unrelated (e.g., outdoor, kitchen, or abstract background).
level_2: Lab bench is present, but only one of the two core materials appears (either raw potato OR white sugar); iodine solution is absent or unidentifiable (e.g., colorless liquid in unlabeled dropper); no addition action shown.
level_3: Lab bench visible; both raw potato (brown-skinned, irregular solid) and white sugar (crystalline, granular, bright white) are present side-by-side on the bench; iodine solution (amber-brown liquid) is held in a dropper or small bottle, but no contact between iodine and either material occurs.
level_4: All elements from 3-score present AND iodine solution is visibly dispensed onto both materials (i.e., amber-brown liquid contacts surface of raw potato AND contacts surface of white sugar), but the spatial arrangement is inconsistent (e.g., materials not left/right as specified, or one material partially occluded, or viewpoint shifts mid-sequence).
level_5: Lab bench visible; raw potato is fully visible on the left side with natural brown skin texture and irregular shape; white sugar is fully visible on the right side as loose, bright white granular crystals; amber-brown iodine solution is dispensed simultaneously or sequentially from a clear dropper/bottle onto each material’s surface; left-right spatial assignment is unambiguous, fixed viewpoint, no occlusion, no repositioning.

Scientific and Causal Correctness rubric:
level_1: No color change observed in either material after iodine contact; or both materials turn identical color (e.g., both black, both blue, both yellow); or color change occurs before iodine contact; or no contact occurs at all.
level_2: Iodine contacts both materials, but only one shows *any* color change, and that change is incorrect (e.g., potato turns yellow instead of blue-black; sugar turns blue-black instead of remaining unchanged); or color change appears on wrong object (e.g., dropper changes color).
level_3: Iodine contacts both materials; raw potato exhibits a localized color change to dark blue-black where contacted; white sugar shows no color change (remains bright white); but the blue-black region on potato is discontinuous, patchy, or fades/reappears inconsistently across frames.
level_4: Iodine contacts both materials; raw potato shows a stable, contiguous, non-fading dark blue-black color change exclusively at the contact site; white sugar remains uniformly bright white with no discoloration, staining, or hue shift anywhere on its surface; however, the blue-black change on potato appears slightly desaturated or lacks visual contrast against potato skin (but still identifiable as blue-black).
level_5: Iodine contacts both materials; raw potato develops a sharply defined, high-contrast, stable dark blue-black color exclusively at the iodine contact site (visually distinct from its original brown skin), with no bleed, fade, or inconsistency across frames; white sugar remains completely unchanged in color, texture, and brightness (no yellowing, browning, wetting-induced translucency, or any perceptible reaction) throughout the entire video.

Spatiotemporal Consistency rubric:
level_1: Objects teleport (e.g., potato appears in new location without motion), vanish/reappear, or undergo impossible deformation (e.g., sugar crystals melt instantly into liquid without heating); lighting flickers violently or shadows jump discontinuously; bench surface warps or fractures between frames.
level_2: One object moves without visible cause (e.g., sugar jumps when iodine is dispensed); dropper tip abruptly changes position without motion path; iodine stream breaks into disconnected blobs mid-air with no trajectory continuity; potato or sugar rotates or tilts without physical interaction.
level_3: All objects remain in fixed positions relative to bench; iodine stream flows continuously from dropper to target; no teleportation, vanishing, or structural breakage; but minor inter-frame jitter occurs (e.g., bench edge wobbles, slight frame-to-frame misalignment of left/right labels), or shadow direction changes once without light source movement.
level_4: No teleportation, vanishing, distortion, or structural breakage; iodine stream maintains continuous, coherent path from dispenser to contact point on each material; lighting and shadow remain fully consistent in direction, intensity, and softness; but one instance of micro-stutter (two identical consecutive frames) or negligible motion blur on dropper hand (not affecting object identity or contact clarity).
level_5: Zero spatiotemporal violation: raw potato remains static and intact on left; white sugar remains static and granular on right; iodine solution flows as a smooth, unbroken, physically plausible stream from dispenser to each material; lighting, shadows, reflections, and perspective remain absolutely stable and self-consistent across all frames; no frame duplication, stutter, blur, or parallax error.