Domain: Natural Science — Microbiology
Target concept: Methylene blue staining (yeast observation)

Video generation prompt: Add one drop of methylene blue stain. Gently place the coverslip on top, avoiding the formation of air bubbles. Observe the specimen under an optical microscope, gradually switching from low to high magnification to examine the yeast cells.

Evaluation guide:
(i) Target concept: Differential staining of yeast viability using methylene blue redox chemistry.
Minimum mechanism: Yeast cells must be metabolically active to reduce methylene blue; reduction requires intact plasma membrane, functional dehydrogenases, and aerobic conditions; stained cells must be viewed under transmitted white light via compound microscope with appropriate magnification.
(ii)Storyline: [Frame 0–2] Glass slide with yeast suspension droplet centered in view → [Frame 3–4] Blue-stained droplet added atop suspension, forming cohesive mixed droplet → [Frame 5–6] Coverslip approached and lowered edge-first, spreading liquid into thin film with no trapped air → [Frame 7] Slide mounted on microscope stage, low-mag view shows scattered oval cells → [Frame 8–9] Objective turret rotates visibly, field narrows, focus sharpens → [Frame 10] High-mag view resolves individual cells showing differential blue intensity in cytoplasm/nucleus. All events occur from fixed frontal overhead + slight oblique microscope-stage viewpoint; microscope eyepiece view is inset or split-screen synchronized with external actions; no cutaways or POV switches.

Manual:
Experimental Procedure
1. Place one drop of yeast suspension on a clean glass slide.
2. Add one drop of methylene blue stain directly onto the suspension.
3. Gently lower a coverslip edge-first onto the stained drop, allowing liquid to spread evenly and excluding air bubbles.
4. Place slide on microscope stage and observe: first at low magnification to locate cells, then switch to high magnification to examine individual yeast cells.
Observation of Experimental Phenomena
Yeast cells appear as oval/ellipsoidal structures; some show budding. Metabolically active cells stain pale blue or remain colorless in cytoplasm with faintly blue nuclei; inactive cells stain deep uniform blue throughout.
Summary of Experimental Principles
Methylene blue is a redox dye: viable yeast cells reduce it to colorless leukomethylene blue, causing pale cytoplasm; non-viable cells retain oxidized blue form. This enables live/dead differentiation under light microscopy.

Prompt Grounding rubric:
level_1: No methylene blue dropper, no yeast suspension droplet, no coverslip, no microscope stage visible; none of the three core actions (adding stain, placing coverslip, observing under microscope) appear.
level_2: At least one of the three core objects appears (e.g., dropper or coverslip), but no action matches the posted_prompt sequence; e.g., coverslip placed before stain added, or microscope absent while stain is applied.
level_3: All three core objects present (methylene blue dropper, yeast suspension droplet on slide, coverslip); stain is added as a single drop onto the specimen, and coverslip is placed, but microscope observation step is missing or shown without magnification progression (e.g., only high-mag view with no transition).
level_4: All three core objects present and correctly used in sequence: (1) one drop of methylene blue stain added to yeast suspension on slide, (2) coverslip gently lowered without air bubbles visible at edges, (3) microscope shown with objective lenses visibly changing from low to high magnification, but either air bubble presence is ambiguous, or coverslip placement motion lacks smooth downward trajectory, or microscope eyepiece view lacks clear cellular detail.
level_5: All three core objects present and correctly used in strict sequence: (1) one distinct drop of methylene blue stain deposited onto yeast suspension on glass slide, (2) coverslip lowered edge-first with continuous smooth motion, resulting in zero visible air bubbles at interface, (3) microscope view transitions visibly and sequentially from low-magnification field (showing multiple yeast cells) to high-magnification field (showing individual yeast cells with stained nuclei and cytoplasm), all within a single unbroken scene.

Scientific and Causal Correctness rubric:
level_1: Methylene blue appears colorless, green, or red; yeast cells appear uniformly bright or fully opaque; no staining contrast between live/dead cells; no cellular morphology visible.
level_2: Stain appears blue but is applied to wrong material (e.g., water, paper); coverslip placed on dry slide; microscope shows blurred or empty field, with no yeast cells visible at any magnification; no color change or contrast in cells after staining.
level_3: Stain is blue and applied to yeast suspension; coverslip placed; microscope view shows yeast cells, but all cells appear uniformly dark blue (no differential staining), or all appear unstained (no blue uptake), or cells lack oval/ellipsoidal shape and budding features typical of Saccharomyces cerevisiae.
level_4: Stain is blue and applied to yeast suspension; coverslip placed; microscope view shows yeast cells with correct oval shape and occasional buds; some cells show pale blue cytoplasm and darker blue nuclei (indicating viability differentiation), but contrast is inconsistent across cells (e.g., >30% cells show identical intensity, violating methylene blue reduction principle), or no clear distinction between metabolically active (pale) and inactive (dark) cells.
level_5: Stain is distinctly blue; applied to viable yeast suspension; coverslip placement yields even monolayer; microscope view at high magnification shows individual yeast cells with morphologically accurate oval shape, occasional budding, and consistent differential staining: metabolically active cells exhibit pale blue or colorless cytoplasm with faintly stained nuclei, while inactive cells show uniformly deep blue cytoplasm and nuclei, matching textbook methylene blue reduction behavior under aerobic conditions.

Spatiotemporal Consistency rubric:
level_1: Objects teleport (e.g., coverslip appears fully placed without motion); sudden lighting shifts or black frames interrupt continuity; slide disappears/reappears; microscope view cuts abruptly without transition.
level_2: Major spatial discontinuity: slide and dropper appear in different lighting/depth planes; coverslip motion jumps across frames; microscope stage rotates or tilts unnaturally; stain droplet changes size/shape discontinuously mid-application.
level_3: All objects remain in fixed relative positions; motion is continuous and physically plausible; lighting and shadow remain consistent; but minor flaws exist: e.g., coverslip edge flickers in/out of focus during placement, or microscope focus ring turns without corresponding image sharpness change.
level_4: All motion is smooth and physically coherent: dropper descends steadily, stain forms cohesive droplet upon contact, coverslip lowers with continuous edge-first contact and spreads liquid evenly; microscope magnification change is accompanied by synchronous focus adjustment and field-of-view shrinkage, but one minor inconsistency exists (e.g., coverslip reflection brightness changes abruptly without lighting shift, or stage moves slightly sideways during focus).
level_5: Zero spatiotemporal violation: dropper approaches slide along straight vertical path; stain contacts surface with immediate cohesive spread; coverslip contacts slide at one edge and rotates down smoothly with full wetting front propagation and zero air entrapment; microscope transition shows seamless, frame-accurate synchronization of lens rotation, field narrowing, and progressive cellular sharpening, all within a single fixed viewpoint with stable illumination and no parallax shift.