Domain: Natural Science — Chemistry
Target concept: Plastic surfaces gradually develop pits, slowly disintegrate, and eventually fragment into smaller particles, causing slight turbidity in the culture medium.

Video generation prompt: Starch-based plastic was placed in a microbial culture medium and incubated at a constant temperature for seven days with time-lapse photography.

Evaluation guide:
(i) Target concept: Enzymatic surface erosion of starch-based bioplastic in aqueous microbial culture, leading to colloidal turbidity via particle release.
Minimum mechanism: Plastic must be solid and insoluble initially; microbes/enzymes act *only at interface*; degradation proceeds top-down (surface pits → subsurface weakening → particle shedding); turbidity arises from suspended colloidal starch fragments, not dissolved molecules (which remain clear).
(ii)Storyline: Frame 1: Intact starch-plastic chip resting on bottom of static culture medium in fixed-view container. Frame 2–3: First visible surface pits form *exclusively on plastic*, no change elsewhere. Frame 4–6: Pits deepen and multiply; turbidity appears *only at plastic-medium contact zone*. Frame 7–9: Turbidity expands outward in continuous gradient; plastic remains whole but increasingly pitted. Frame 10: Plastic still macroscopically intact, surface heavily pitted, medium turbid near plastic with soft radial falloff, no isolated turbid regions or detached particles unattached to plastic.

Manual:
Experimental Procedure
1. Place a solid starch-based plastic chip into a transparent microbial culture medium in a stationary container.
2. Maintain constant temperature and fixed side-view camera angle.
3. Capture time-lapse frames showing 7-day degradation process compressed into 10 seconds.
Observation of Experimental Phenomena
- Initial: Smooth, intact plastic surface; clear medium.
- Mid-sequence: Localized pits appear on plastic surface; slight turbidity emerges adjacent to plastic.
- Final: Progressive increase in turbidity radiating from plastic; plastic remains solid but surface-disrupted; no free-floating fragments before final stage.
Summary of Experimental Principles
Starch-based plastic undergoes microbial enzymatic hydrolysis: surface erosion forms pits → bulk disintegration releases soluble oligomers → colloidal particles cause turbidity in aqueous medium.

Prompt Grounding rubric:
level_1: No starch-based plastic object is visible; or no culture-medium container is shown; or the plastic is never placed into the medium; or nothing suggests a multi-frame/time-lapse sequence (e.g. it is a single static image with no progression).
level_2: The plastic object is present but shaped wrong for this setup (e.g. shown as powder, liquid, or thin film rather than a solid chip or pellet); or the container is present but looks like an unrelated vessel (e.g. clearly labeled saline or plain water rather than a culture medium); or the plastic is dropped or poured in rather than placed; or there is no visible passage of time across the clip.
level_3: A solid, non-powdery starch-based plastic piece sits inside a transparent container holding a clear-to-faintly-hazy liquid; the container looks like a standard lab vessel (Petri dish or test tube) with a consistent, uniform shape; the sequence shows the plastic being placed, then a period of stillness, then the first sign of change near the plastic; no object appears or is swapped out partway through.
level_4: Everything required at the 3-point level holds, and in addition the plastic keeps a consistent matte, off-white/beige, non-glossy appearance throughout, the container stays in the same fixed position and orientation, the liquid outside the immediate area around the plastic stays level and undisturbed, and no object is added or removed from the scene between frames.
level_5: Everything required at the 4-point level holds, and in addition the plastic starts the clip with a smooth surface and defined edges, the camera holds one fixed framing on the container for the entire clip with no zoom or repositioning, and the container and plastic remain the same relative size and position from the first frame to the last.

Scientific and Causal Correctness rubric:
level_1: The plastic dissolves instantly or disappears; the medium turns fully cloudy right away; the plastic changes to an unrelated color like blue, green, or red; the plastic floats up or bubbles vigorously; or nothing in the clip visually ties the plastic to the medium becoming turbid.
level_2: The plastic shows changes unrelated to microbial erosion (melting, swelling, unexplained discoloration, or dissolving away); turbidity spreads evenly through the whole medium with no connection to the plastic's location; loose fragments appear before any surface pitting is shown; or the medium looks clearer partway through than it did earlier.
level_3: The plastic stays solid and keeps roughly its starting shape and size at the outset; small pits or depressions (not scratches or cracks) appear on its surface; turbidity first shows up in the liquid right next to the plastic and grows gradually over the clip; no loose particles break free before the pitting is well underway; and the haze stays within the liquid itself rather than settling as sediment or floating as foam.
level_4: Everything required at the 3-point level holds, and in addition the pits form only on the plastic's surface (not on the container walls or floating in the medium), the turbidity keeps increasing over time rather than fading or leveling off, and no unrelated specks or debris appear in the medium that aren't connected to the plastic's degradation.
level_5: Everything required at the 4-point level holds, and in addition the pits are clearly visible before the turbidity becomes noticeable, the haze appears first right at the plastic's surface and fades out gradually with distance from it rather than showing patches of cloudiness far from the plastic, and any visible fragments by the end of the clip are still attached to or just breaking off from the plastic rather than appearing already suspended on their own.

Spatiotemporal Consistency rubric:
level_1: The plastic or container jumps to a different location or orientation between frames with no connecting motion; the lighting swings abruptly from dark to bright with no transition; the plastic disappears and then reappears; or the clip visibly stutters or freezes as if frames were dropped.
level_2: The plastic's outline flickers or warps between frames; the container's edge bulges or pinches inconsistently; a shadow points a different way than the visible light source would suggest; the liquid surface ripples or flows with no apparent cause; or the camera rotates or zooms with no reason given in the scene.
level_3: The camera framing stays fixed; the container and plastic keep the same relative position and size; the lighting stays steady with no flashes or sudden brightness changes; the plastic's surface and the container's transparency look physically reasonable throughout; and no object appears to pass through or overlap another in a way that breaks physical sense.
level_4: Everything required at the 3-point level holds, and in addition all motion in the clip is smooth rather than jerky or skipping; the plastic's surface pitting builds up gradually across frames rather than appearing fully formed where none existed the frame before; and the spreading haze forms a smooth, continuous gradient rather than showing hard, blocky boundaries between cloudy and clear regions.
level_5: Everything required at the 4-point level holds, and in addition the container walls show no visible bending or warping in any frame, the plastic's outline stays clearly defined and consistent from frame to frame, the haze reads as a soft, natural gradient rather than patches that switch on and off, and the camera framing and object scale stay identical from the first frame to the last with no drifting perspective.