Domain: Natural Science — Biophysics
Target concept: Escherichia coli diffuses directionally from the high-concentration side to the low-concentration side, eventually leading to a uniform bacterial concentration on both sides.

Video generation prompt: Two connected transparent chambers, one filled with a culture medium containing fluorescently labeled *E. coli*, and the other with sterile culture medium, were observed by time-lapse imaging to monitor the concentration of *E. coli* on both sides under no external forces.

Evaluation guide:
(i) Target concept: Net, diffusion-like spread of live, motile bacteria across a concentration gradient in the absence of directional bias.
Minimum mechanism: E. coli must be capable of self-propelled, energy-dependent motility (flagellar rotation driven by the proton-motive force), producing locally random run-and-tumble movement; the barrier must permit passage without imposing directionality; no chemotactic, hydrodynamic, or electromagnetic cues bias movement toward either chamber, so the net population-level spread from high to low concentration resembles passive diffusion even though individual cells are actively swimming.
(ii)Storyline: Frame 1: Two side-by-side transparent chambers, left chamber filled with discrete fluorescent dots, right chamber empty of fluorescence. Barrier visible and intact. → Frame sequence shows progressive, symmetric entry of fluorescent dots into right chamber while left chamber density declines. No dot crosses barrier before neighboring dots begin crossing. → Final frames show a non-uniform but bimodal distribution (not yet fully uniform), confirming ongoing spread. Viewpoint remains fixed; no occlusion; all motion is local, jittery, and non-coordinated.

Manual:
Experimental Procedure
1. Place two identical transparent chambers side-by-side, separated by a permeable barrier.
2. Fill left chamber with fluorescently labeled E. coli culture medium; fill right chamber with sterile culture medium.
3. Begin time-lapse imaging with fixed viewpoint and no external perturbation.
Observation of Experimental Phenomena
Initially, fluorescent signal is present only in the left chamber; over time, fluorescent signal appears and increases in the right chamber while decreasing in the left chamber; signal never appears outside the chambers or in the barrier.
Summary of Experimental Principles
E. coli cells actively swim via flagellar motility, an energy-dependent process; because no chemical gradient or other directional cue biases their movement, their net population spreads from high concentration (left) to low concentration (right) until it approaches equilibrium — a diffusion-like pattern arising from undirected, not passive, motion.

Prompt Grounding rubric:
level_1: The video does not show two chambers with fluorescently labeled E. coli and a barrier between them at all: e.g., only one chamber, no fluorescence, or an unrelated scene with no progression over time.
level_2: Two chamber-like regions appear, but they are not both transparent, or they are not placed next to each other, or the fluorescent signal doesn't look like discrete bacterial dots (e.g., it's a uniform glow instead), or the second (sterile) chamber can't be told apart from the first.
level_3: Two transparent chambers sit next to each other; one contains many small, distinct fluorescent dots consistent with bacteria while the other starts with no fluorescent dots; at least two moments in the video show a different amount of fluorescence in each chamber, establishing that time is passing.
level_4: All elements of score 3 are present, and additionally the fluorescent dots are present only in the originally-labeled chamber at the very first moment and appear in both chambers later on, and nothing else (hands, pipettes, on-screen text) enters or blocks the view of either chamber during the video.
level_5: All elements of score 4 are present, and additionally the fluorescent dots stay confined within the two chambers (none appear in the barrier between them or outside the chambers' outlines), the two chambers' positions relative to each other never change, and no dot appears out of nowhere or vanishes without visibly moving there first.

Scientific and Causal Correctness rubric:
level_1: Fluorescent dots move the wrong way (accumulating first in the originally sterile chamber), or the two chambers' dot counts never change relative to each other throughout the whole video, or dots vanish and reappear discontinuously, or the dots swim in obviously coordinated, aligned paths rather than moving individually.
level_2: Dots are already present in both chambers from the very first moment (no initial concentration difference to observe), or dots leave the original chamber entirely with none remaining there, or the two chambers reach equal fluorescence instantly with no visible in-between stage, or the dots clump together or dissolve rather than behaving like individual bacteria.
level_3: Dots start out only in one chamber and, over the course of the video, some appear in the other chamber while the original chamber's dot count visibly drops; nothing in the shot suggests an external push (no visible flow, stirring, or pressure difference driving the dots).
level_4: All elements of score 3 are present, and additionally the dot count in the originally-labeled chamber keeps decreasing over time (not fluctuating up and down) while the other chamber's dot count keeps increasing, with no sudden jump such as the second chamber going from empty to full in one step.
level_5: All elements of score 4 are present, and additionally individual dots keep a consistent size and shape as they move (none merge, split, fade out, or bloom in place), and no dot crosses into the second chamber well before nearby dots have started moving too: the spread looks like many individual bacteria drifting without direction rather than one bacterium being pushed ahead of the rest.

Spatiotemporal Consistency rubric:
level_1: The chambers or the barrier between them suddenly change size, rotate, or jump position between moments; fluorescent dots blink into or out of existence without moving there; the barrier disappears or bends; the lighting suddenly shifts color or brightness in a way unrelated to the time-lapse.
level_2: The chambers shift left/right or up/down between moments; the barrier flickers or briefly becomes invisible; fluorescent dots stretch, smear, or warp unnaturally; the motion looks jerky, or the same frame appears to repeat with no change in between.
level_3: The chambers' outlines stay put and continuous throughout; the barrier stays visible in the same place; the fluorescent dots move along smooth, continuous paths rather than jumping from one spot to another; the overall brightness and contrast stay steady with no pulsing or flashing.
level_4: All elements of score 3 are present, and additionally the dots' movement looks fluid rather than stepping in place, the transparency and sharpness of the chamber walls stay the same throughout, and the camera's viewpoint never shifts: the chamber edges stay in the same relative position across the whole video.
level_5: All elements of score 4 are present, and additionally the dots' frame-to-frame movement looks continuous with no stutter or trailing ghost images, the chambers' shape, alignment, and spacing never change, and the image never blurs, warps, or drifts out of focus in a way that isn't explained by the dots' own motion.