Domain: Natural Science — Biophysics
Target concept: Fluorescent glucose diffuses radially from the point of addition, forming a gradient, and eventually becomes uniformly fluorescent throughout the culture dish.

Video generation prompt: Add cell culture medium to a transparent dish, and drop a fluorescently labeled glucose solution on one side. Fix the position and perform time-lapse imaging.

Evaluation guide:
(i) Target concept: Passive molecular diffusion in aqueous biological medium.
Minimum mechanism: Glucose molecules move randomly due to thermal energy; net movement occurs down concentration gradient; container is static, isotropic, and unbounded at macro-scale; fluorescence signal linearly reports local concentration.
(ii)Storyline: Frame 1: Static dish with clear medium + single bright fluorescent droplet on left/right side. → Causal transition: Diffusion initiates at interface. → Frame 2–N−1: Fluorescence expands as a contiguous, radially symmetric halo; intensity decreases monotonically with distance from origin; no flow, convection, or boundary trapping. → Causal transition: Gradient drives net solute flux until equilibrium. → Final frame: Uniform fluorescence intensity across entire dish area; no residual gradient or hotspots. Perspective: Fixed overhead view; dish rim fully visible; no occlusion; lighting enables clear discrimination of intensity variations.

Manual:
Experimental Procedure
1. Place transparent circular cell culture dish on stable surface.
2. Fill dish evenly with clear cell culture medium.
3. Using a pipette, place a single droplet of fluorescently labeled glucose solution on one side of the medium surface.
4. Fix camera viewpoint directly above dish; begin time-lapse recording.
Observation of Experimental Phenomena
A bright fluorescent spot appears at the droplet site, then expands radially outward as a continuous intensity gradient; over time, fluorescence fills the entire dish uniformly.
Summary of Experimental Principles
Fluorescent glucose diffuses radially from the point of addition, forming a concentration gradient, and eventually achieves uniform distribution throughout the medium via passive diffusion.

Prompt Grounding rubric:
level_1: No transparent culture dish appears; no fluorescently labeled glucose droplet is visible anywhere in the scene; there's no sign of time-lapse structure (no fixed camera position, no sequence of frames showing the dish changing over time); the dish shown, if any, contains no visible medium.
level_2: A stationary transparent dish holding cell culture medium is visible, but the fluorescent glucose droplet is missing, sits in the wrong place (e.g., centered rather than to one side), or multiple droplets appear instead of one; the frames don't show any progression over time: they all look identical or appear in no coherent order.
level_3: A transparent dish filled with cell culture medium is shown from a fixed overhead viewpoint; a single fluorescent glucose droplet sits on one side of the dish; at least two frames show visibly different fluorescence patterns, confirming a time-lapse rather than a single static shot.
level_4: Everything at the 3-point level holds, and in addition the droplet's starting side never changes across the sequence; fluorescence first appears right where the droplet met the medium and then spreads outward from that spot over successive frames, without the bright region jumping to a new location, splitting into separate patches, or disappearing.
level_5: Everything at the 4-point level holds, and in addition frame 1 shows the droplet as one clearly bounded, high-intensity bright spot; the fluorescence brightness visibly fades in a continuous gradient from that spot outward at each intermediate frame; by the last frame the entire dish reads as evenly fluorescent, with no frame along the way showing the glow shrink back, retreat toward the origin, or spread in a non-circular pattern such as a streak or clump.

Scientific and Causal Correctness rubric:
level_1: The dish reads as uniformly fluorescent right from the start, or the glow fades away entirely over time, or the droplet changes color/shape without any spreading, or the fluorescence creeps only along the dish's rim or appears to move out of the liquid plane rather than spreading across the surface. No radial spreading pattern is present at all.
level_2: The droplet is visibly fluorescent, but either it never spreads outward at all, or it spreads in a shape that isn't radial (a stripe, a wedge, an uneven blob), or it advances as separate, disconnected bright patches rather than one continuous front; no brightness gradient forms between the origin and the rest of the dish.
level_3: Fluorescence starts at the droplet's side of the dish and visibly spreads outward over time; a brightness gradient is visible: brighter near the origin, dimmer with distance; the fluorescent area grows across successive frames, but the dish has not yet reached full, even brightness by the last frame.
level_4: Everything at the 3-point level holds, and in addition the brightness gradient stays radially even around the droplet's origin point rather than favoring one direction; the fluorescent front keeps advancing without gaps or sudden jumps and never pulls back toward the origin; the dish does not turn uniformly bright before the final frame.
level_5: Everything at the 4-point level holds, and in addition the sequence moves cleanly from a single bright spot, to a radial gradient, to full even brightness across the dish, in that order; no frame ever shows a region far from the droplet brighter than a region close to it; no frame shows the brightness jumping in sharp, discrete rings or bands, and the fluorescence never appears to flow, swirl, or move like discrete particles rather than spreading smoothly.

Spatiotemporal Consistency rubric:
level_1: The dish or the droplet's origin point jumps to a different spot between frames; the glow disappears and then reappears; the dish's shape, tilt, or transparency changes partway through; the illumination flashes or pulses in a way unrelated to the diffusion itself; frames appear out of chronological order (e.g., a later, more-spread-out frame appears before an earlier, less-spread-out one).
level_2: The dish itself stays put, but the droplet's starting point visibly shifts sideways between frames in a way that isn't just the glow spreading; the fluorescent region skips over intermediate area instead of growing into it gradually; the overall brightness of the scene jumps up or down abruptly partway through the clip; the dish rim or background reflections change in a way that breaks visual continuity from one frame to the next.
level_3: The dish stays in the same place, shape, and orientation throughout, and the droplet's origin point does not move; the fluorescent region grows outward smoothly with no jump or gap in coverage; the dish's brightness and the visibility of its rim stay steady enough that the growing glow is easy to track in every frame, with no tearing, warping, or clipping of the dish or its contents.
level_4: Everything at the 3-point level holds, and in addition the fluorescent front's outward growth has no frame-to-frame gaps in the area it covers; its edge doesn't suddenly sharpen or blur in a way inconsistent with ordinary diffusion; the dish rim and background stay flicker-free between frames.
level_5: Everything at the 4-point level holds, and in addition the dish rim stays in the exact same place and shape in every frame; the droplet's original spot stays visually fixed with no perceptible drift; the fluorescent boundary keeps softening gradually and evenly as it would from true diffusion, with no jagged edges, sparkling artifacts, or flickering intensity anywhere along the front.