Domain: Natural Science — Biochemistry & Molecular Biology
Target concept: Fermentation of sugar by yeast produces carbon dioxide (CO₂) bubbles over time.

Video generation prompt: Place two glass jars containing warm water and dry yeast side by side; dissolve sugar only in the left jar, then fit identical balloons over both jar openings and show the jars over a time-lapse of about an hour at room temperature.

Evaluation guide:
(i) Target concept: Microbial metabolic activity (fermentation) requires a fermentable substrate (sugar) to generate gaseous product (CO₂).
Minimum mechanism: Yeast cells must be viable and metabolically active in warm aqueous environment; sugar must be present to serve as carbon/energy source; CO₂ production must be physically trapped to produce observable mechanical work (balloon inflation): here the gas is captured by the balloon as it forms, so it shows up as gradual balloon inflation rather than as bubbles breaking the liquid's surface; absence of sugar must result in negligible CO₂ output under same conditions.
(ii)Storyline: [Phase 1: Setup] Two jars enter frame side-by-side; warm water and dry yeast are added to both; sugar is added exclusively to left jar; identical balloons are fitted over openings; all actions visible, sequential, and unambiguous. [Phase 2: Causal Pause] Shown as an accelerated time-lapse spanning roughly an hour: no external intervention, no motion except gradual left-balloon expansion. [Phase 3: Differential Outcome] Left balloon transitions from shrunken to taut and rounded; right balloon retains original crumpled morphology; contrast is visually stable, sustained, and attributable solely to sugar presence. Perspective: Fixed frontal, eye-level, full-jar framing; all critical details (jar contents, balloon state, spatial relation) simultaneously visible without occlusion or parallax ambiguity.

Manual:
Experimental Procedure
1. Place two identical transparent glass jars side-by-side on flat surface.
2. Add equal volumes of warm water and equal amounts of dry yeast to both jars.
3. Add sugar only to left jar; leave right jar sugar-free.
4. Fit identical uninflated balloons tightly over both jar openings.
5. Let stand at room temperature and observe over an accelerated time-lapse of about an hour.
Observation of Experimental Phenomena
Left jar balloon inflates visibly and continuously over the time-lapse; right jar balloon remains flat and unchanged. The liquid surfaces in both jars stay visually calm throughout, since the balloon captures the CO₂ as it forms rather than letting it bubble through the liquid.
Summary of Experimental Principles
Yeast ferments sugar anaerobically, producing carbon dioxide gas; CO₂ accumulates inside left jar and inflates its balloon; no sugar = no fermentation = no CO₂ = no inflation in right jar.

Prompt Grounding rubric:
level_1: The two glass jars are missing warm water, dry yeast, or sugar entirely; no balloon sits over either jar opening; the two jars are never shown together in the same shot; sugar is missing from the left jar, or is added to both jars or neither; none of the setup actions described in the prompt are shown.
level_2: Two containers appear, but they are not matching glass jars (for example different shapes, or a jar paired with a bottle); one jar is missing its warm water or yeast; sugar ends up in both jars, in neither jar, or in the wrong jar; the balloons are missing, are different sizes or colors, or are not actually fitted over the jar openings; the two jars are shown in separate shots rather than together.
level_3: Two matching glass jars sit next to each other in one continuous shot; both contain warm water and dry yeast; a visible amount of sugar (distinct grains from the yeast) sits in the left jar only; identical balloons are stretched over both jar openings; every object named in the prompt (the two jars, the yeast, the sugar, and the balloons) appears in the right place.
level_4: All the requirements for a 3 are met here too, plus: the jars are clear enough to see the liquid inside; before the sugar is added, the yeast looks like a fine beige granular layer rather than a dissolved slurry; the sugar in the left jar looks like distinct white crystals; both balloons sit snugly over their jar rims with no visible gap or lopsided fit; no spoon, hand, or label lingers in frame once the setup is finished.
level_5: All the requirements for a 4 are met here too, plus: nothing transient (a passing hand, condensation streaking the glass, a glare) blocks the view of either jar's contents; both jars are filled to the same level with a matching liquid surface; the balloon material looks smooth and un-creased in a way consistent with simply being stretched over the opening, not manually inflated; the camera frames both jars fully and consistently, without zooming or cropping either one out.

Scientific and Causal Correctness rubric:
level_1: Neither balloon shows any sign of inflation; both balloons stay equally flat and motionless the entire time; there is no visible difference between the sugared jar and the sugar-free jar; nothing in the video ties the presence of sugar to any change in either balloon.
level_2: A balloon inflates, but it is the wrong one: the right (sugar-free) jar's balloon inflates instead of, or along with, the left one; or the left balloon inflates even though no sugar was shown going into that jar; or a balloon is inflated by something other than gradual gas buildup, such as someone visibly blowing into it or squeezing the jar.
level_3: The left jar's balloon slowly changes from loose and shrunken to rounded and taut; the right jar's balloon stays loose and shrunken the whole time; this difference in balloon shape is the only notable change in the scene, and it lines up with sugar being present only in the left jar, consistent with fermentation gas being generated only where the yeast has sugar to consume.
level_4: All the requirements for a 3 are met here too, plus: the left balloon keeps growing without deflating and reinflating in cycles; the CO2 produced in the left jar shows up as balloon inflation rather than as bubbling or fizzing at the liquid's surface in either jar, consistent with the balloon capturing the gas as it forms; the right balloon never puffs out or changes shape on its own.
level_5: All the requirements for a 4 are met here too, plus: the left balloon's expansion looks smooth and gradual rather than jumping in sudden bursts as it grows; the balloon's surface stays evenly rounded and taut as it grows, without sagging on one side; no water droplets or condensation form inside the left balloon; the right balloon keeps its original creases and folds unchanged from start to finish, showing that no internal pressure ever built up inside it.

Spatiotemporal Consistency rubric:
level_1: One of the jars suddenly appears somewhere else on the surface, or vanishes and pops back into view, without anything shown moving it; a balloon disappears from a jar's opening and reappears out of nowhere; the whole scene abruptly switches from bright to dark lighting with no transition; a jar or balloon bends or stretches in a way real glass or rubber never would, such as a jar wall curving inward on its own; the time-lapse cuts or jumps between different moments with no transition, as if separate shots were spliced together mid-observation.
level_2: One jar visibly shifts position relative to the other partway through the clip with nothing shown causing it; a balloon's fit over its jar's rim changes from loose to snug (or the reverse) with no visible cause; the light in the scene flickers, or the shadows the jars cast swing to a different angle for no reason; the video looks noticeably jerky or stutters, as though frames were skipped or repeated.
level_3: The two jars stay in the same spots relative to each other for the whole clip, with nothing jumping, bending, or breaking apart; the glow and reflections on the curved glass of each jar shift together in a way that matches a camera that never moves; both balloons keep their rubbery sheen and texture as the left one inflates, without suddenly looking like a different material; if the left balloon moves at all, it swells outward gradually the way a real balloon would, never floating or hovering off the jar's rim.
level_4: All the requirements for a 3 are met here too, plus: there is no small back-and-forth shake in either jar's outline from frame to frame; the two jars do not appear to drift sideways relative to each other as if the camera itself had shifted; neither jar's round shape nor the balloons' curves look stretched or squashed as if seen through a moving lens; no frame repeats itself or blurs into the next one.
level_5: All the requirements for a 4 are met here too, plus: the left balloon's surface does not show blocky discoloration or an uneven, streaky color pattern as it inflates; the pace of the left balloon's growth stays consistent with how blurred or sharp its edge looks: a fast-looking swell is never paired with a perfectly crisp, unmoving outline; both jars and balloons stay in equally sharp focus throughout, with neither one going soft while the other stays clear; the reflections of the room on both jars' glass match each other throughout, since both jars sit under the same unmoving light and camera.