Domain: Healthcare — Pathophysiology
Target concept: Candida fungus

Video generation prompt: Take tissue sections from Candida fungal infection, perform PAS staining (periodic acid-Schiff staining), rinse with water, mount, and observe under a light microscope.

Evaluation guide:
(i) Target concept: PAS staining enables specific visualization of Candida fungal elements in tissue sections via glycogen/polysaccharide detection.
Minimum mechanism: Periodic acid must oxidize fungal cell wall carbohydrates to dialdehydes; Schiff reagent must then form magenta adducts exclusively where dialdehydes are present; water rinse must selectively remove unbound Schiff reagent without eluting bound magenta complexes; mounting medium must preserve optical clarity without dissolving or diffusing the stain.
(ii)Storyline: [Frame 0–2] Tissue section lies flat on glass slide under diffuse lab light. [Frame 3–4] PAS reagent dispensed and spreads uniformly: immediate onset of faint magenta in fungal structures. [Frame 5–6] Water rinse flows across section: background magenta fades while fungal magenta intensifies and sharpens. [Frame 7] Mounting medium applied: forms glossy, bubble-free seal over stained section. [Frame 8–10] Microscope view transitions smoothly into focus and reveals high-contrast magenta yeast cells with eccentric buds AND pseudohyphae with constricted septa, all in same focal plane; no host cell staining. Perspective remains fixed overhead (slide) → lateral (staining) → direct ocular (microscope); fungal structures must remain continuously visible and morphologically stable across all transitions.

Manual:
Experimental Procedure
1. Place thin tissue section on clean glass slide.
2. Apply PAS reagent; wait for magenta color development.
3. Rinse gently with distilled water to remove excess stain.
4. Apply mounting medium and cover with coverslip.
5. Observe under light microscope at 400× magnification.
Observation of Experimental Phenomena
Magenta-stained Candida yeast cells (round/ovoid, 3–5 µm) with eccentric budding, and/or pseudohyphae (elongated, constricted at septa) against pale pink background.
Summary of Experimental Principles
Candida fungi contain abundant glycogen and polysaccharides in cell walls; PAS oxidation of vicinal diols yields aldehydes that bind Schiff reagent, producing diagnostic magenta color — selective for fungal elements in infected tissue.

Prompt Grounding rubric:
level_1: None of the required elements (a tissue section, PAS reagent application, a water rinse, mounting medium, or a light-microscope view) appear at all; no staining or mounting step of any kind is shown.
level_2: At least one element appears (a slide, or a microscope view) but the section-then-PAS-reagent-then-water-rinse-then-mounting-then-microscope sequence isn't shown in order (for instance mounting appears before staining), or the fungal shapes shown don't read as Candida at all (no round yeast-like or filamentous shapes).
level_3: All five steps appear in the correct order: section on slide, PAS reagent applied (visible magenta liquid or stain layer), water rinse (visible flow or wash motion), mounting medium applied (clear viscous layer), and a final light-microscope field showing some structures, with round or branching shapes that could be Candida, but their color or shape isn't yet confirmed as fungal-specific.
level_4: Everything in level 3 holds, plus the objects at each step are correctly typed (translucent section, magenta-colored reagent, clear rinse liquid displacing the stain, a uniform glossy mounting layer, a focused microscope field with round/ovoid or branching shapes) and nothing is skipped, duplicated, or misplaced, but the final magenta coloring or shape stays ambiguous, e.g. no clear budding pattern or septal constriction is visible.
level_5: Everything in level 4 holds, plus the final microscope field clearly shows both round/ovoid budding yeast cells and true pseudohyphae with visible constrictions at their septa, all magenta-stained, sharply in focus, and at a consistent scale within the same field, with nothing duplicated, omitted, misplaced, or shown out of sequence.

Scientific and Causal Correctness rubric:
level_1: No magenta coloring appears anywhere, or the shapes it does color are clearly not fungal (resembling bacteria or blood cells rather than yeast or hyphae); the tissue shows no sign that a fungus is present at all; there is no visible connection between applying the PAS reagent and any magenta appearing.
level_2: Magenta color does appear but isn't selective: it colors the whole tissue field roughly equally rather than concentrating on the fungal shapes, or it dominates the background instead of the fungal structures; the water-rinse step produces no visible change (the magenta looks identical before and after, or vanishes completely).
level_3: Magenta color concentrates on the fungal-looking shapes but also lingers, weaker, in some surrounding tissue (a faint magenta tint in nearby connective tissue or cell nuclei, for example); the water rinse visibly lightens this background tint while the fungal magenta stays strong; the magenta intensity in the fungal shapes is visibly and consistently higher than in the surrounding tissue at every step after the rinse.
level_4: The magenta signal is confined almost entirely to the fungal shapes, appearing only very faintly if at all in surrounding host tissue (cell nuclei, connective fibers, blood cells) after rinsing, and the mounting step adds no visible color shift or distortion to the fungal magenta, but one small flaw remains, such as a faint residual magenta tinge lingering in one small patch of non-fungal tissue, or slightly uneven magenta intensity across the fungal shapes.
level_5: After rinsing, the magenta signal appears exclusively on the fungal shapes with zero visible tint left anywhere in host tissue (nuclei, connective fibers, and blood cells all read as their normal pale background color); the water rinse is what causes the non-fungal tint to fade while the fungal magenta holds steady or intensifies; the mounting step introduces no haze, halo, or color shift to the magenta signal; the sequence (reagent applied, magenta appears, rinse removes non-specific color while preserving fungal color) is unambiguous across the whole clip.

Spatiotemporal Consistency rubric:
level_1: The slide seems to jump straight from hand to microscope stage with no transit shown; the PAS reagent appears already fully coating the section with no application motion; the microscope view suddenly shows a different magnification or focus than the previous frame; the frame's brightness flips suddenly between bright and dark; the fungal shapes blink out of view and return with no visible cause.
level_2: The PAS reagent appears to already be sitting on the slide with no visible application motion; the water rinse shows no fluid actually moving across the slide; the mounting medium looks dry or absent right before the 'applied' step; the microscope view's focus or field of view changes abruptly between steps with no smooth transition; the fungal shapes shift position or size between steps for no visible reason.
level_3: The slide stays in place on the bench or stage throughout; the reagent, water, and mounting medium each visibly contact and move across the slide's surface when applied; the microscope view stays centered on the same patch of tissue; the fungal shapes keep a consistent orientation, size, and location across every step, aside from one small remaining flaw, such as a brief flicker in illumination brightness or one instant where a fungal shape's edge looks slightly soft.
level_4: Everything in level 3 holds, plus: the slide keeps the same orientation throughout; the PAS reagent flows onto the section and spreads evenly; the water rinse visibly flows across the section in one direction, displacing the excess reagent; the mounting medium spreads out smoothly with no bubbles or gaps at the edges; once the microscope view is reached, it keeps the same field, focus, and magnification throughout the observation, with no unexplained jump; the fungal shapes never rotate, shear, or distort during any step.
level_5: Every step shows physically plausible motion (the reagent visibly drips and spreads, the rinse water visibly sheets across and recedes, the mounting medium visibly oozes and settles), with no skipped frames or jarring jumps in motion; the slide never shifts sideways or rotates; the fungal shapes stay in the same position and orientation across all five steps; the lighting falls off naturally and consistently, as expected under steady lab-bench illumination; there is no camera parallax, lens-like distortion, or perspective warp during the transition into the microscope view.