Domain: Natural Science — Microbiology
Target concept: E. coli exhibits a negative citrate utilization test: it lacks the citrate-permease system needed to use citrate as a sole carbon source, so Simmons citrate medium remains green rather than changing to blue.

Video generation prompt: E. coli was inoculated into citrate medium and cultured at 37°C, followed by photography of the resulting color of the medium.

Evaluation guide:
(i) Target concept: Visual demonstration of a negative citrate utilization test for E. coli, the classic organism used to show that a facultative anaerobe unable to use citrate as its sole carbon source leaves Simmons citrate agar unchanged.
Minimum mechanism: E. coli lacks the citrate-permease system needed to bring citrate into the cell as a carbon/energy source under these conditions; without citrate catabolism there is no net alkalinization of the medium, so the bromothymol blue indicator stays at its green baseline instead of shifting to blue; the tube should show viable E. coli growth (e.g., visible surface streaking) without any accompanying color shift.
(ii)Storyline: Frame 1: Green Simmons citrate agar slant in a labeled tube, sterile loop approaching. Frame 2: Loop contacts the medium surface (visible streak/stab). Frame 3: Incubator environment implied (e.g., warm glow, timer overlay, or blurred incubator door). Frame 4: Same tube, still showing the same green slant surface after the incubation period. Frame 5 (optional for 5-point): side-by-side comparison, an uninoculated green control tube next to the inoculated tube, both still green. All frames maintain a fixed viewpoint, consistent lighting, and an unoccluded medium surface; no off-screen action changes the outcome.

Manual:
Experimental Procedure
1. Sterile inoculating loop touches E. coli colony.
2. Loop streaks the surface of a Simmons citrate agar slant (green).
3. Tube incubated at 37°C (implied by lab context).
4. After incubation, photograph the medium surface.
Observation of Experimental Phenomena
Simmons citrate agar remains uniformly green in the inoculated tube; no blue color develops.
Summary of Experimental Principles
E. coli is citrate-negative: it lacks the citrate-permease needed to take up citrate as a sole carbon source, so it cannot metabolize the citrate in Simmons citrate medium. Without that metabolism there is no alkaline shift, so the bromothymol blue indicator stays green (pH near neutral) instead of turning blue (pH ≥7.6) — unlike citrate-positive organisms such as Klebsiella pneumoniae or Enterobacter aerogenes, which do turn the medium blue.

Prompt Grounding rubric:
level_1: No citrate-medium container is shown; no E. coli inoculation action appears; there is no cue that incubation at 37°C took place; there is no before/after view of the medium's color.
level_2: A citrate-medium container appears but is not clearly identifiable as Simmons citrate agar; either the inoculation action or the incubation cue is shown, but not both; the medium's color is inconsistent with a plausible baseline (e.g., shown as colorless, brown, or already blue from the start).
level_3: The container is clearly identifiable as a Simmons citrate agar slant/tube by its shape and green color; the E. coli inoculation action is visibly shown (loop touching, stabbing, or streaking the surface); 37°C incubation is implied by the surrounding lab context (an incubator cue, a warm ambient look, or a time-lapse indicator); the medium is shown green both near the start and near the end of the clip, but the two moments are not shown close enough together for an easy comparison.
level_4: Everything in score 3 holds, and the green medium is shown at the start and again at the end in a single continuous shot or a clearly ordered sequence, with no confusing intermediate color (no sudden yellow, brown, or mottled patch); the container stays in the same position and framing throughout; the inoculation and incubation cues are clearly tied to the same tube.
level_5: Everything in score 4 holds, and additionally the clip shows an inoculated tube next to an untouched control tube, both visibly green and labeled or otherwise distinguishable from each other; the inoculation action is shown touching only the experimental tube, never the control; nothing blocks the view of either tube's surface; no lighting effect or color cast makes the green look different between the two tubes.

Scientific and Causal Correctness rubric:
level_1: The medium changes color at all (to blue, yellow, or any hue other than its starting green), or the tube is shown starting at some other baseline color and ending green, or E. coli is shown growing in an unrelated medium (e.g., a lactose broth or blood agar) instead of citrate agar.
level_2: The medium's color shifts slightly (e.g., a faint teal or grayish tint creeps in) rather than staying a clean green throughout; or growth, turbidity, or patchiness is shown that implies a chemical change even though the hue itself is still nominally green; or the clip implies the wrong organism or condition caused the outcome (e.g., an anaerobic-looking sealed tube, or an emphasized incubation temperature other than 37°C).
level_3: The medium is shown as a consistent green both before and after the incubation period, using the same tube throughout; there is no partial shift toward blue anywhere on the visible surface; but no clear inoculation action is shown touching that specific tube, so the link between 'E. coli was added' and 'it stayed green' is not reinforced.
level_4: Everything in score 3 holds, and the inoculation action is shown contacting the same tube that later still reads green; no other liquid or reagent is added partway through that could explain the lack of change; the green color does not fade, darken, or shift at any point in the final frames.
level_5: Everything in score 4 holds, and additionally the green looks even and fully saturated across the whole visible slant surface with no patchy or two-toned areas; there is no stray color cast (no odd magenta or blue fringe from lighting) that could be mistaken for the start of a color shift; the scene gives no visual suggestion that the tube was sealed away from air or otherwise kept from the normal aerobic incubation conditions E. coli can grow under.

Spatiotemporal Consistency rubric:
level_1: The container disappears from one shot and reappears in a different position; the medium's surface abruptly warps or looks broken; the lighting flickers wildly or its color cast shifts mid-sequence; the inoculation loop appears already touching the medium with no approach motion shown; background objects jump in size or position between frames.
level_2: The container stays in frame but its tilt or rotation changes inconsistently between shots; the medium's surface texture suddenly looks different (e.g., smooth then grainy) with nothing to explain it; the direction the shadows fall changes noticeably between consecutive shots; the inoculation motion skips: the loop seems to jump partway to its final position rather than moving continuously.
level_3: The container stays still, with the same framing and orientation throughout; the medium's surface keeps a consistent texture and shape; the inoculation action shows one continuous motion from the loop approaching to it making contact; the overall brightness and the direction of the shadows stay about the same from shot to shot; nothing enters or leaves the frame unexpectedly.
level_4: Everything in score 3 holds, and the slant's angle, the curve of the medium's surface, and how translucent or opaque the medium looks stay the same in every shot; the container and whatever is behind it do not appear to shift relative to each other as the camera holds its position; there is no visible jitter, sudden zoom, or moment where the shot goes soft and then sharp again.
level_5: Everything in score 4 holds, and additionally the container's edges, the contour of the medium's surface, and the tip of the inoculation tool stay clearly aligned from one frame to the next with no visible drift; no motion blur hides where the loop meets the surface; there is no strobing, repeated-frame look, or ghosting at any point, including during the inoculation motion.