Domain: Healthcare — Digestive Physiology
Target concept: Bile pH Test (Paper Strip Method)

Video generation prompt: Prepare a bile sample in a clean test tube. Using forceps, take a pH indicator strip and quickly immerse it in the bile sample, then remove it. Place the strip flat and allow a few seconds for stabilization. Compare the strip with a standard pH color chart to determine the pH value.

Evaluation guide:
(i) Target concept: Alkaline pH confirmation in human bile via reversible acid-base indicator chemistry.
Minimum mechanism: Bile must be physiologically sourced (not simulated), contain sufficient bicarbonate to raise pH above 7.0; indicator dye must be immobilized on porous paper matrix; color transition must occur solely due to H+ concentration shift, not oxidation or drying artifacts.
(ii)Storyline: Frame 1–2: Static shot of clean test tube containing translucent yellow-green bile (no bubbles, no particulates). Frame 3–4: Forceps enter frame, grasp dry beige/tan strip. Frame 5–6: Strip descends continuously into bile, full submersion visible (meniscus displacement evident). Frame 7–8: Strip lifts fully out, surface liquid film visible, no dripping. Frame 9: Strip placed flat, lies unmoving, fully extended, no curl. Frame 10: Strip and chart appear side-by-side in same plane, both fully in focus, lighting uniform, color comparison directly observable.

Manual:
Experimental Procedure
1. Place bile sample in clean test tube.
2. Using forceps, pick up pH indicator strip and fully immerse it in bile.
3. Remove strip and place it flat on a stable surface.
4. Compare strip color to standard pH color chart.
Observation of Experimental Phenomena
Bile is translucent yellow-green liquid; strip changes from beige/tan to stable bluish-green; matched chart band reads a specific alkaline value such as pH 7.5.
Summary of Experimental Principles
Bile is alkaline (typically pH 7–8) because hepatocytes and bile duct cells secrete bicarbonate into it; commercial pH indicator strips carry a blended, multi-dye universal indicator (for example a mix of bromothymol blue, phenol red, and thymol blue) rather than a single dye, so the paper shifts continuously from yellow-green near neutrality to teal and then blue-violet as pH rises through the 6.0–9.0 range. Because the dyes in the blend have staggered transition points, the dried strip can be matched to one specific half-unit band (7.0, 7.5, 8.0, or 8.5) on the reference chart rather than only signaling a broad acid/alkaline split, and a match in the 7.0–8.5 region confirms bicarbonate-rich, physiologically normal bile.

Prompt Grounding rubric:
level_1: No test tube of bile, no pH indicator strip, no forceps, and no pH color chart appear anywhere in the video; no dipping, withdrawal, or side-by-side comparison of strip and chart is depicted at any point.
level_2: Only some of the required props show up (for example a test tube, a strip, forceps, or a chart appears alone), but they are never combined into the pick-up-dip-compare sequence; the strip may be shown floating with no forceps holding it, or a chart appears with no strip anywhere near it, and the strip never contacts the bile liquid.
level_3: The yellow-green bile in its test tube, the pH indicator strip, the forceps, and the color chart are all shown, and the forceps carry the strip toward the test tube's opening, but the strip's tip never actually touches the liquid surface before the shot moves on.
level_4: Forceps lower the strip fully into the bile, lift it back out, and set it down flat, and the strip and chart both eventually appear on screen together, but the pairing is not cleanly viewable: the chart is cropped at the frame edge, tilted so its printed bands are hard to read, or the strip is shown blurred or at a steep angle that hides its dyed face from the camera.
level_5: The full pick-up, dip, withdraw, lay-flat sequence plays out without skipping a step, and in the closing shot the strip rests flat directly next to the color chart with the strip's entire dyed length and the chart's full set of printed bands unobstructed, sharply in focus, and visible at the same time, so a viewer could read off which band the strip lines up with, regardless of whether that happens to be the physiologically correct one.

Scientific and Causal Correctness rubric:
level_1: Bile is shown as clear/colorless, blood-red, or opaque white instead of its normal yellow-green pigmentation; the strip's dye pad stays its original beige/tan color even after full contact with the liquid; the reference chart carries no pH labeling at all (e.g., an unlabeled rainbow strip or bare numbers); nothing on screen ties the act of dipping to any resulting color.
level_2: Bile appears as the expected viscous yellow-green liquid, but the strip's dye pad does not shift color at all after immersion and stays beige/tan; or the strip does change color yet the chart shown has no band anywhere near that hue family; or the chart's visible labels stop at pH 1–5, leaving no alkaline band for anything to be matched against.
level_3: Bile is correctly the translucent yellow-green liquid; the strip's dye pad shifts from beige/tan toward blue-green after immersion; the chart carries labeled green-through-blue bands, but the strip's resulting hue lines up with an acidic label (e.g., pH 5.0) rather than any alkaline band, contradicting the fact that bicarbonate secretion normally keeps bile alkaline, around pH 7–8.
level_4: Bile is correctly the translucent yellow-green liquid; the strip's dye pad shifts to a distinct teal/blue-green after immersion; the chart shows four separately labeled bands (pH 7.0, 7.5, 8.0, 8.5) each with a visibly different hue; the strip's resulting color lines up with one of these four bands, but the strip is still visibly damp at the moment of comparison, darkening or streaking the hue, or the chart is lit unevenly enough that picking the correct band is a guess.
level_5: Bile is correctly the translucent yellow-green liquid with no sediment or froth; the strip starts dry and, within a few seconds of being lifted out, settles into one stable teal-to-blue hue with no further drift; the chart is evenly lit and matte, with four distinctly colored bands clearly labeled 7.0, 7.5, 8.0, and 8.5; the dried strip's hue lines up cleanly with exactly one of those bands (e.g., 7.5), with no streaking, fading, or glare to make the match ambiguous.

Spatiotemporal Consistency rubric:
level_1: The bile-filled test tube vanishes mid-shot and reappears already full with no pouring or refilling shown; the strip jumps straight from the forceps' jaws onto the chart with no in-between travel frames; the scene hard-cuts from normal bench lighting to near-total darkness partway through; the forceps visibly buckle or the test tube's glass wall splits open with no force ever applied to cause either.
level_2: One clear spatiotemporal break occurs: the strip enters the frame already glistening wet before ever touching the bile; the forceps open and let go of the strip in mid-air with no visible landing; the color chart appears on screen before the strip has even been lifted out of the test tube; or the bile's liquid level jumps up or down between the immersion shot and the withdrawal shot with no matching cause.
level_3: The test tube stays put on the bench the entire time; the forceps stay visible on screen for the whole pick-up-dip-lift motion without vanishing and reappearing at a new grip point; the strip's path runs continuously from the forceps to the bile surface to the flat resting spot to beside the chart, with no segment of that path skipped or the strip flickering out of view.
level_4: Everything required for score 3 holds, and in addition: the dip-and-lift motion runs smoothly with no stutter or freeze-frame; the strip comes to rest completely flat with no curling or tilting; once the strip and chart are both in frame, they hold a fixed position relative to each other with no sudden jump in camera angle between them; the lab bench and any other background objects stay in the same place and shape they had in earlier frames.
level_5: Every prop's motion is unbroken from first appearance to final rest: the forceps, strip, test tube, and chart never skip a frame of travel; the test tube's round cross-section, the strip's rectangular edges, and the chart's grid of band borders all stay geometrically intact with no warping; and once the strip is set down beside the chart for the final comparison, the bench lighting is still coming from the same angle and brightness as when the bile was first shown, so no new shadow or glare could make the strip's actual dyed color look like a different chart band than it truly matches.